Musculoskeletal

Osteomalacia and vitamin D deficiency

Clinical Overview and When to Suspect Osteomalacia

— In children, the same process affects the growth plate and is called rickets.

— Distinct from osteoporosis, which is loss of bone mass with normal mineralization.

— Vitamin D (cholecalciferol/ergocalciferol) → 25-OH-D in liver → 1,25-(OH)₂-D in kidney (1α-hydroxylase, PTH-driven)

— 1,25-(OH)₂-D increases intestinal Ca²⁺ and PO₄³⁻ absorption

— Deficiency → low Ca/PO₄ → secondary hyperparathyroidism → phosphaturia → undermineralized osteoid

— Adult with diffuse bone pain, proximal muscle weakness, waddling gait, difficulty rising from a chair

— Atraumatic or low-trauma fractures, especially femoral neck, pelvis, ribs

— Risk-laden patient: housebound elder, dark skin in northern latitude, veiling/sun avoidance, malabsorption (celiac, Crohn, post-bariatric), chronic liver disease, CKD stage 4–5, chronic anticonvulsants (phenytoin, phenobarbital), rifampin, cholestyramine

— Labs incidentally showing low Ca, low PO₄, high ALP, high PTH, low 25-OH-D

— ~25% of U.S. adults have 25-OH-D <20 ng/mL; frank osteomalacia is rarer but underdiagnosed

— Peak presentation in winter/spring; common in nursing-home residents

Definition: Osteomalacia is defective mineralization of mature bone matrix (osteoid) in adults, most commonly from vitamin D deficiency but also from phosphate wasting, hypophosphatasia, or aluminum/bisphosphonate toxicity.

Pathophysiology primer:

When to suspect on Step 3:

Epidemiology pearls:

Board pearl: The classic Step 3 stem is an elderly woman with vague back/hip pain, proximal weakness, and a hip fracture after a minor fall, with labs showing ↓Ca, ↓PO₄, ↑ALP, ↑PTH. Don't anchor on osteoporosis — check 25-OH-D before starting a bisphosphonate, because giving bisphosphonates in untreated osteomalacia worsens hypocalcemia.

Step 3 management framing: This is largely an outpatient/family medicine problem — your job is recognition, lab confirmation, repletion, and monitoring at 3 months, plus addressing the underlying cause (malabsorption, CKD, drug effect).

Presentation Patterns and Key History

— Diffuse bone pain — dull, aching, worst in lower back, hips, pelvis, ribs; tender to pressure (sternum, tibia)

— Proximal muscle weakness — difficulty climbing stairs, rising from chair, lifting arms; waddling (Trendelenburg) gait

— Fragility fractures — femoral neck, pubic ramus, ribs, vertebrae; often after trivial trauma

— Sun exposure: time outdoors, sunscreen use, latitude (>37°N limits winter UVB), clothing coverage

— Diet: dairy intake, fortified milk/cereal, fatty fish, supplements; vegan or lactose-intolerant?

— GI history: celiac disease, Crohn, chronic pancreatitis, Roux-en-Y gastric bypass, sleeve gastrectomy, short-bowel

— Hepatobiliary: cirrhosis, primary biliary cholangitis (impaired 25-hydroxylation, bile salt loss)

— Renal: CKD stage, dialysis (impaired 1α-hydroxylation → calcitriol deficiency)

— Medications: phenytoin, phenobarbital, carbamazepine, rifampin (induce CYP24A1, accelerate vitamin D catabolism), glucocorticoids, cholestyramine, orlistat, antiretrovirals (tenofovir → Fanconi)

— Skin: Fitzpatrick V–VI (melanin reduces cutaneous synthesis ~5-fold)

— Functional: falls, mobility, housebound status, nursing-home residence

— Family hx: X-linked hypophosphatemic rickets, hypophosphatasia, kidney stones

— Weight loss, night sweats, focal bone pain → rule out malignancy/myeloma

— Steatorrhea, iron-deficiency anemia → screen celiac with tTG-IgA

Symptom triad to anchor on:

Tempo: Insidious over months to years. Patients often misattributed to "arthritis," fibromyalgia, or depression before diagnosis.

High-yield history checklist (Step 3 family-medicine voice):

Red-flag overlaps to ask about:

Key distinction: Osteomalacia pain is diffuse and symmetric with proximal weakness; metastatic bone disease or multiple myeloma typically gives focal, progressive, night-worse pain ± hypercalcemia. Both can fracture, but the lab signature differs (myeloma: ↑Ca, normal ALP often).

Board pearl: A post-bariatric patient 2–5 years out with bone pain and proximal weakness is osteomalacia until proven otherwise — bypass of duodenum/jejunum impairs Ca and fat-soluble vitamin absorption.

Physical Exam Findings

— Often appears chronically ill, deconditioned; may use cane/walker

— Waddling gait from proximal hip-girdle weakness — a Step 3 buzzword

— Difficulty with sit-to-stand without using arms (proximal weakness screen)

— Bony tenderness to direct pressure over sternum, anterior tibia, ribs, iliac crests, pubic symphysis

— Diffuse point tenderness without erythema or swelling distinguishes from inflammatory arthritis

— Spinal tenderness, kyphosis if vertebral compression fractures

— Pelvic compression test may elicit pain (insufficiency fracture)

— Chvostek and Trousseau signs if symptomatic hypocalcemia

— Carpopedal spasm, perioral paresthesias in severe deficiency

— Proximal weakness 4/5 in hip flexors, shoulder abductors; DTRs preserved or brisk (unlike myopathies with hyporeflexia)

— No sensory deficits — if present, think B12 or peripheral neuropathy

— Gait: short stride, broad base, Trendelenburg lurch

— Craniotabes (softened skull in infants), frontal bossing, delayed fontanelle closure

— Rachitic rosary (costochondral beading), Harrison groove, bowed legs (genu varum), widened wrists/ankles, delayed dentition

— Joint swelling/effusion → think RA, PMR, septic arthritis

— Focal mass or skin lesions → malignancy

— Hepatosplenomegaly → infiltrative disease

— Timed Up and Go (TUG) ≥12 sec → fall risk

— Chair stand test, grip strength

— Falls in past year (≥2 falls or 1 injurious fall triggers fall workup)

General appearance:

Musculoskeletal exam:

Neuromuscular:

Rickets findings (pediatric counterpart, board context):

Findings that argue against osteomalacia:

Functional assessment to document (Step 3 outpatient flavor):

Board pearl: Proximal muscle weakness + bone pain + normal CK is classic osteomalacia. If CK is elevated, reconsider polymyositis, statin myopathy, or hypothyroid myopathy.

Step 3 management: Always pair the exam with a fall-risk assessment and home-safety counseling — osteomalacia patients are at extreme fracture risk, and addressing throw rugs, lighting, and footwear is testable preventive care.

Diagnostic Workup — Initial Labs

— 25-hydroxyvitamin D (25-OH-D) — the screening test of choice; reflects body stores

— Serum calcium (total + albumin, or ionized) and phosphorus

— Alkaline phosphatase (ALP) — typically elevated in osteomalacia

— Intact PTH

— Creatinine/eGFR and BUN

— Magnesium (hypomagnesemia impairs PTH release and vitamin D activation)

— 24-hour urine calcium and creatinine (or spot Ca/Cr ratio) — low in deficiency

— 25-OH-D <20 ng/mL (often <10)

— Serum Ca: low-normal or low

— Phosphorus: low (from secondary hyperparathyroidism)

— ALP: elevated (often 2–4× ULN, bone isoenzyme)

— PTH: elevated (secondary hyperparathyroidism)

— 24-h urine Ca: low (<100 mg/d)

— Deficient: 25-OH-D <20 ng/mL (50 nmol/L)

— Insufficient: 20–29 ng/mL

— Sufficient: ≥30 ng/mL (Endocrine Society for at-risk patients; IOM accepts ≥20 for general population)

— Toxic: >100 ng/mL (risk of hypercalcemia)

— Short half-life, tightly PTH-regulated, can be normal or high in deficiency

— Reserve for suspected 1α-hydroxylase deficiency, CKD, granulomatous disease (sarcoid → ↑1,25), or tumor-induced osteomalacia

— tTG-IgA + total IgA → celiac

— LFTs, albumin, INR → hepatic synthesis

— TSH, SPEP/UPEP, free light chains → mimics

— FGF23 if hypophosphatemia with normal vitamin D

Core panel (order all together):

Classic lab signature of nutritional vitamin D deficiency osteomalacia:

Vitamin D status thresholds (Endocrine Society / IOM):

Do NOT routinely order 1,25-(OH)₂-D for screening:

Adjunct labs by suspected etiology:

Board pearl: The PTH-driven phosphaturia is why phosphate is low in nutritional osteomalacia despite normal kidneys — secondary hyperparathyroidism inhibits proximal tubular phosphate reabsorption (downregulates NaPi-2a).

Key distinction: Osteoporosis labs are normal (normal Ca, PO₄, ALP, PTH, 25-OH-D). Abnormal mineral panel + bone pain = osteomalacia, not osteoporosis — switch your workup.

Diagnostic Workup — Advanced or Confirmatory Studies

— Plain radiographs of symptomatic sites: generalized osteopenia, blurred trabeculae, codfish vertebrae

— Looser zones (pseudofractures): pathognomonic — transverse radiolucent bands perpendicular to cortex, classically at medial femoral neck, pubic rami, ribs, scapular borders, ulna — Step 3 buzzword

— DXA: low bone density (T-score often <–2.5) — useful but cannot distinguish osteomalacia from osteoporosis; check mineral panel before treating low DXA as osteoporosis

— Bone scan (Tc-99m): multiple symmetric uptake foci ("superscan" or hot Looser zones); useful when fractures are suspected but radiographs negative

— MRI: insufficiency fractures with marrow edema

— Gold standard but rarely needed clinically

— Shows increased osteoid thickness, prolonged mineralization lag time (>100 days), and decreased mineralization front

— Reserve for atypical cases, suspected hypophosphatasia, or failure to respond to repletion

— ↓25-OH-D, ↓Ca, ↓PO₄, ↑PTH, ↑ALP → nutritional vitamin D deficiency (most common)

— Normal 25-OH-D, ↓PO₄, normal/↑PTH, phosphaturia → renal phosphate wasting → check FGF23

— High FGF23: tumor-induced osteomalacia (TIO) — small mesenchymal tumor; obtain Ga-68 DOTATATE PET/CT or octreotide scan to localize; also X-linked hypophosphatemic rickets

— Low FGF23 with phosphaturia: Fanconi syndrome (check urine glucose, amino acids, bicarb — proximal RTA)

— ↓Ca, ↓25-OH-D, normal/high 1,25-D, high PTH, malabsorption signs → celiac/IBD/post-bariatric

— ↓ALP, normal/high Ca, low PLP, history of premature tooth loss → hypophosphatasia (don't give bisphosphonates!)

— CKD stage 4–5 with ↓1,25-D, ↑PTH, ↑PO₄ → renal osteodystrophy spectrum

Imaging — when and what:

Bone biopsy with tetracycline double-labeling:

Workup by laboratory pattern (decision logic):

Step 3 management: A 25-OH-D level and basic mineral panel cost <$50 and answer the question in 90% of patients — order them before DXA-driven osteoporosis pharmacotherapy.

Board pearl: Pseudofractures on the medial femoral neck in a middle-aged woman with proximal weakness = osteomalacia. Don't call it a stress fracture and send to ortho — treat the deficiency.

Risk Stratification and First-Line Management Logic

— Severe: 25-OH-D <10 ng/mL, symptomatic hypocalcemia, fractures, or marked weakness

— Moderate: 25-OH-D 10–20 with biochemical changes (low Ca/PO₄, high PTH/ALP)

— Insufficient: 25-OH-D 20–29, asymptomatic, no biochemical changes

— Nutritional/sun-deficient → repletion + maintenance, counseling

— Malabsorption (celiac, IBD, bariatric, pancreatic insufficiency) → high-dose oral or parenteral D, treat primary disease

— Drug-induced (anticonvulsants, rifampin, glucocorticoids) → higher maintenance doses (often 2–5×), consider drug switch if feasible

— CKD → use calcitriol or paricalcitol (active form), not cholecalciferol alone, because 1α-hydroxylation is impaired

— Hepatic → cholecalciferol still effective; consider calcifediol if severe cholestasis

— Phosphate wasting (TIO, XLH) → phosphate replacement + calcitriol; burosumab (anti-FGF23 mAb) for XLH and TIO

— IV calcium gluconate if tetany, seizures, QT prolongation, or Ca <7.5 with symptoms

— Otherwise oral calcium carbonate/citrate 1000–1500 mg elemental/day during repletion

— Correct magnesium before/during — hypomagnesemia blocks PTH and vitamin D action

— Recheck 25-OH-D, Ca, PO₄, PTH, ALP at 8–12 weeks after starting repletion

— ALP and PTH normalize over 3–6 months; bone pain improves in weeks

Step 1 — Confirm and classify severity:

Step 2 — Identify and address the underlying cause:

Step 3 — Replete calcium first if symptomatic hypocalcemia:

Step 4 — Choose repletion regimen (see chunk 7).

Step 5 — Monitor:

CCS pearl: In a CCS-style case, the order set for suspected osteomalacia is: CBC, CMP, magnesium, phosphorus, 25-OH-D, intact PTH, 24-h urine Ca, ALP (bone fraction if needed), tTG-IgA, plus plain films of symptomatic sites. Then choose repletion based on severity and etiology.

Board pearl: Never start a bisphosphonate, denosumab, or romosozumab in a patient with unrecognized vitamin D deficiency — risk of severe hypocalcemia. Always confirm 25-OH-D ≥30 and corrected calcium normal before antiresorptive therapy.

Pharmacotherapy — First-Line Repletion

— D₃ raises 25-OH-D more efficiently and sustains levels longer

— D₂ acceptable, especially for vegans (plant-derived) and is the form available as prescription 50,000 IU capsules in the U.S.

— Ergocalciferol 50,000 IU PO weekly × 8 weeks (or cholecalciferol 6,000 IU daily × 8 weeks)

— Total loading dose ~300,000–600,000 IU

— Recheck 25-OH-D at 8–12 weeks; if <30, repeat 8-week course

— Maintenance: 1,500–2,000 IU cholecalciferol daily (Endocrine Society for at-risk adults)

— 50,000 IU twice weekly × 6–8 weeks, or even daily dosing

— Post-bariatric: 50,000 IU 1–3 times weekly indefinitely; consider calcifediol (25-OH-D₃) which bypasses hepatic 25-hydroxylation and is better absorbed

— Refractory cases: IM cholecalciferol 300,000 IU every 3–6 months

— Elemental calcium 1,000–1,200 mg/day total (diet + supplement)

— Calcium citrate preferred in achlorhydria, PPI users, post-bariatric (does not require acid)

— Calcium carbonate with meals otherwise; cheaper, more elemental Ca per pill

— Split doses (≤500 mg at a time) for absorption

— Calcitriol (1,25-(OH)₂-D₃) 0.25–0.5 mcg/day for CKD stage 4–5, dialysis, hypoparathyroidism, 1α-hydroxylase deficiency, severe hepatic disease

— Paricalcitol or doxercalciferol in dialysis (less hypercalcemia)

— Monitor closely — narrow therapeutic window, risk of hypercalcemia/hypercalciuria

— Mineral panel + 25-OH-D at 8–12 weeks, then every 6–12 months

— Hold/reduce if 25-OH-D >100, Ca >10.5, or urine Ca >300 mg/d

— Anticonvulsant users: double maintenance dose; consider 50,000 IU monthly

— Glucocorticoids: ≥2,000 IU/d maintenance

— Orlistat, cholestyramine, mineral oil: separate dosing by 4 hours

Vitamin D₃ (cholecalciferol) preferred over D₂ (ergocalciferol):

Standard repletion (deficient, 25-OH-D <20):

Severe deficiency or malabsorption:

Calcium co-repletion:

Active vitamin D analogs — when indicated:

Monitoring during therapy:

Drug interactions/pearls:

Step 3 management: Document diet counseling (fortified dairy, fatty fish 2×/wk, fortified cereals), 15–30 min midday sun 2–3×/wk on arms/legs when feasible, and a written follow-up plan at 3 months.

Expanded Pharmacology and Adjuncts

— Hypercalcemia, hypercalciuria, nephrolithiasis, nephrocalcinosis, AKI

— Anorexia, nausea, constipation, polyuria, confusion

— Usually with sustained 25-OH-D >100 ng/mL or daily intake >10,000 IU long-term

— Treatment: stop vitamin D and calcium, IV saline, loop diuretic if euvolemic, glucocorticoids (reduce 1,25-D), bisphosphonates if severe, hemodialysis in extreme cases

— Vitamin D is fat-soluble — toxicity may persist weeks to months

— Thiazides + high-dose vitamin D: thiazides reduce urinary Ca excretion → hypercalcemia risk; monitor

— Digoxin + hypercalcemia: potentiates digoxin toxicity — check both

— PPIs: reduce calcium carbonate absorption — use citrate

— Sevelamer, calcium acetate in CKD: phosphate binders that also affect Ca balance

— Calcium carbonate 40% elemental — cheap, take with food, avoid in achlorhydria

— Calcium citrate 21% elemental — preferred with PPI, post-bariatric, elderly; can take without food

— Avoid calcium from coral/oyster shell (lead contamination concern)

— Neutral phosphate (K-Phos Neutral) 1–2 g elemental PO divided 4–5×/d (must dose frequently due to short half-life)

— Combine with calcitriol 0.25–0.75 mcg/d to prevent secondary hyperparathyroidism

— Monitor PTH, urine Ca, renal US for nephrocalcinosis

— Approved for X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO) when surgical cure not feasible

— SC q2–4 weeks; restores phosphate reabsorption

— Monitor phosphate, do not combine with phosphate + active D (risk of hypercalcemia)

Toxicity recognition (vitamin D excess):

Special drug scenarios on Step 3:

Calcium formulations — choosing wisely:

Phosphate therapy (for phosphate-wasting osteomalacia):

Burosumab (anti-FGF23 monoclonal):

When TIO is found and tumor localized: surgical resection is curative — phosphate and ALP normalize within weeks. Use Ga-68 DOTATATE PET/CT to find the (often tiny) somatostatin-receptor–expressing mesenchymal tumor.

Board pearl: A patient with refractory hypophosphatemic osteomalacia, normal vitamin D, and high FGF23 needs DOTATATE imaging — the answer is a hidden mesenchymal tumor, often in bone or soft tissue of extremities or sinuses.

Special Populations — Elderly and Renal/Hepatic Impairment

— Reduced cutaneous 7-dehydrocholesterol → less D synthesis per sun exposure (~25% of young adult)

— Less sun exposure (housebound, nursing-home)

— Reduced dietary intake, lactose intolerance

— Decreased renal 1α-hydroxylase activity

— Screen at-risk elders (housebound, recurrent falls, fractures, dark skin, malabsorption)

— Maintenance: 800–2,000 IU/d cholecalciferol; combine with 1,000–1,200 mg Ca

— USPSTF (2018): insufficient evidence to recommend universal vitamin D screening or supplementation in community-dwelling adults to prevent falls/fractures — but treat identified deficiency and continue supplementation in institutionalized elders (separate evidence base for fall reduction)

— Polypharmacy review: anticonvulsants, glucocorticoids, PPIs, loop diuretics, levothyroxine — many interact

— Stage 3a–b: 25-OH-D often low — replete with cholecalciferol

— Stage 4–5/dialysis: 1α-hydroxylase activity falls → low 1,25-D despite adequate 25-OH-D → secondary hyperparathyroidism with hyperphosphatemia, hypocalcemia, ↑PTH

— Treat with calcitriol or analogs (paricalcitol, doxercalciferol), phosphate binders (sevelamer, lanthanum, calcium acetate), calcimimetics (cinacalcet, etelcalcetide) for refractory hyperparathyroidism

— Avoid high calcium intake → vascular calcification risk

— KDIGO: keep PTH 2–9× ULN in dialysis patients

— Severe cirrhosis impairs 25-hydroxylation only modestly — cholecalciferol still works

— Cholestatic disease (PBC, PSC): fat malabsorption + reduced bile salts → use higher doses or calcifediol (25-OH-D₃) which is water-miscible

— Monitor for coexisting K, A, E deficiencies

— Vitamin D 800 IU/d in institutionalized elderly reduces fall risk (older meta-analyses); benefit in community-dwelling is debated

— Combine with exercise (balance + strength), home-safety eval, medication review, vision check for full fall-prevention bundle

Elderly (Step 3 high-yield):

CKD spectrum (renal osteodystrophy/CKD-MBD):

Hepatic impairment:

Falls and fractures:

Step 3 management: In CKD stage 4 with hypocalcemia and high PTH, the right answer is calcitriol, not cholecalciferol alone — the kidney can't activate the precursor.

Board pearl: Don't equate low 25-OH-D in CKD with simple nutritional deficiency — always check phosphate, PTH, and consider active analogs.

Special Populations — Pregnancy, Pediatrics, and Other Subgroups

— Maternal vitamin D crosses placenta; deficiency → neonatal hypocalcemia, congenital rickets, enamel hypoplasia

— RDA: 600 IU/d; many experts recommend 1,000–2,000 IU/d in at-risk women (veiled, dark-skinned, northern latitude, obese)

— Routine universal screening not recommended; screen if symptomatic, malabsorptive, or prior affected infant

— Calcium: 1,000 mg/d (1,300 if adolescent pregnancy)

— Breastfed infants: human milk is low in vitamin D — all exclusively or partially breastfed infants need 400 IU/d cholecalciferol starting in first days of life (AAP)

— Formula-fed infants taking ≥1 L/d get adequate D from fortified formula

— Bowed legs after walking age, delayed motor milestones, irritability

— Craniotabes, frontal bossing, rachitic rosary, Harrison groove, widened wrists, delayed fontanelle closure, delayed dentition

— Labs as in adults; wrist radiograph shows widened, frayed, cupped metaphysis

— Treat: 2,000 IU/d for ≤1 year, 6,000 IU/d for older children × 6–12 weeks, then 400–1,000 IU maintenance

— Calcium 30–75 mg/kg/d elemental during treatment

— Pubertal growth spurt + poor diet + limited sun exposure → at-risk

— Athletes with female athlete triad: bone stress reactions warrant 25-OH-D check

— Vitamin D sequestered in adipose tissue → lower bioavailability; obese patients need 2–3× the dose

— Post-Roux-en-Y or biliopancreatic diversion: lifelong supplementation — 3,000–6,000 IU/d with target 25-OH-D >30; calcium citrate 1,200–1,500 mg/d; annual labs

— Need ~5–10× longer sun exposure for equivalent synthesis — empiric supplementation often warranted

— Cultural sensitivity; emphasize oral supplementation over sun exposure counseling

— Prophylactic vitamin D 1,000–2,000 IU/d standard of care

Pregnancy and lactation:

Pediatric rickets (Step 3 family-medicine recognition):

Adolescents:

Obesity and bariatric surgery:

Dark skin (Fitzpatrick V–VI):

Veiled/sun-avoidant patients:

Anticonvulsant therapy (especially institutionalized patients on chronic phenytoin/phenobarbital):

Board pearl: A breastfed infant with seizures and hypocalcemia in winter = neonatal vitamin D deficiency / congenital rickets. The mother is often also deficient. Treat both.

Complications and Adverse Outcomes

— Fragility fractures: femoral neck, pubic ramus, vertebrae, ribs — major source of disability and mortality in the elderly (1-year mortality after hip fracture ~20–30%)

— Looser zones / pseudofractures progressing to complete fractures

— Vertebral compression fractures → height loss, kyphosis, restrictive lung pattern, GERD

— Bone deformity in chronic disease: bowing of long bones, protrusio acetabuli, triradiate pelvis

— Worsened osteoporosis when coexisting

— Severe proximal myopathy → loss of independence, falls

— Tetany, carpopedal spasm, laryngospasm, seizures from hypocalcemia

— Prolonged QT interval → torsades risk

— Paresthesias, neuromuscular irritability (Chvostek, Trousseau)

— Severe hypocalcemia: heart failure, hypotension, refractory dysrhythmias

— Long-standing secondary hyperparathyroidism → tertiary hyperparathyroidism with autonomous PTH secretion and hypercalcemia (especially in CKD)

— Hypophosphatemia <1.0 mg/dL: rhabdomyolysis, respiratory muscle weakness, hemolysis

— Vitamin D toxicity: hypercalcemia, nephrolithiasis, nephrocalcinosis, AKI

— Hypercalciuria from over-replacement → stones, CKD

— Milk-alkali syndrome from excessive calcium carbonate

— Severe hypocalcemia if antiresorptives (bisphosphonates, denosumab) given to untreated osteomalacia patients — Step 3 testable

— Chronic pain, depression, deconditioning, social isolation

— Loss of independence; nursing-home placement after hip fracture

— Permanent growth retardation, dental defects, deformity requiring orthopedic correction

— Cardiomyopathy from severe hypocalcemia in infants

Skeletal complications:

Neuromuscular complications:

Cardiovascular and metabolic:

Iatrogenic complications:

Psychosocial:

In rickets (children):

Step 3 management: After hip fracture in an elderly patient with low 25-OH-D, the discharge plan must include vitamin D + calcium repletion, osteoporosis evaluation (DXA, secondary causes), fall-prevention referral (PT/OT, home safety), and fracture-liaison service follow-up. Failure to initiate secondary prevention after a fragility fracture is a quality-of-care gap.

Board pearl: Symptomatic hypocalcemia with prolonged QT in a chronically ill elder → check 25-OH-D, Mg, and corrected Ca; treat with IV calcium gluconate, replete magnesium, then oral repletion.

When to Escalate Care — Consultation and Inpatient Triage

— Asymptomatic or mild–moderate symptoms

— Corrected Ca ≥7.5 mg/dL, no tetany, no QT prolongation

— No acute fracture

— Reliable follow-up

— Symptomatic hypocalcemia: tetany, carpopedal spasm, laryngospasm, seizures

— Corrected Ca <7.0 mg/dL even if mildly symptomatic

— QT prolongation, arrhythmia

— Severe hypophosphatemia <1.0 mg/dL with weakness, respiratory compromise, or rhabdomyolysis

— Acute fragility fracture requiring surgical intervention

— IV calcium gluconate 1–2 g in 50 mL D5W over 10–20 min, then continuous infusion if persistent (0.5–1.5 mg elemental Ca/kg/h)

— Telemetry, ECG

— Replete magnesium (2–4 g IV MgSO₄) — without magnesium, calcium won't normalize

— Begin oral calcium + calcitriol early (calcitriol acts faster than cholecalciferol)

— Workup as above: 25-OH-D, PTH, PO₄, Mg, Cr, ALP, urine Ca

— Endocrinology: refractory cases, suspected tumor-induced osteomalacia, hypophosphatasia, hereditary disorders (XLH), tertiary hyperparathyroidism, complex CKD-MBD

— Nephrology: CKD stage 4–5, dialysis, suspected Fanconi syndrome

— Gastroenterology: malabsorption workup, celiac, IBD, post-bariatric complications

— Orthopedics: acute fracture, surgical fixation, persistent pseudofracture

— Oncology/Surgery: localized mesenchymal tumor in TIO

— PM&R/PT: rehab after fracture, gait training, fall prevention

— Dietitian: malabsorption, post-bariatric, vegan patients

— Reconcile every supplement and prescription

— Schedule 3-month follow-up with mineral panel

— Provide written instructions on doses, sun exposure, falls prevention

— Communicate clearly with PCP — incomplete handoff after hip fracture is a leading patient-safety gap

Outpatient management is appropriate for most cases:

Admit for IV calcium and inpatient repletion when:

CCS triage logic (initial orders for symptomatic hypocalcemia):

Subspecialty consultation:

Hospital-to-home transition pearls:

CCS pearl: For tetany from hypocalcemia: order IV calcium gluconate, IV magnesium, ECG, telemetry, oral calcitriol 0.5 mcg, oral cholecalciferol 50,000 IU, BMP q6h until Ca >8.0, then transition to oral. Don't use calcium chloride peripherally — extravasation causes severe necrosis.

Key Differentials — Same-Category (Metabolic Bone) Causes

— Normal Ca, PO₄, ALP, PTH, 25-OH-D

— Reduced bone mineral density (T ≤ –2.5) without mineralization defect

— Postmenopausal women, glucocorticoid users, hypogonadism

— Key distinction: Same DXA findings as osteomalacia, but labs are normal. Always check mineral panel before treating osteoporosis pharmacologically.

— High Ca, low PO₄, high PTH, high 24-h urine Ca, normal/high ALP

— "Stones, bones, abdominal groans, psychiatric overtones"

— Osteitis fibrosa cystica: brown tumors, subperiosteal resorption (radial side of phalanges), "salt-and-pepper" skull

— Treat with parathyroidectomy if symptomatic or per guidelines

— High PTH driven by hyperphosphatemia and low calcitriol

— High PO₄, low/normal Ca, low 1,25-D, high PTH, high ALP

— Overlaps with osteomalacia in CKD; both can coexist (mixed renal osteodystrophy)

— Long-standing secondary becomes autonomous → hypercalcemia despite resolved trigger

— Often post-renal transplant

— Markedly elevated ALP with normal Ca and PO₄

— Focal bone deformity, bowing tibia, enlarged skull, hearing loss, warm bone

— Imaging: lytic/sclerotic mixed lesions, cortical thickening, "cotton wool" skull

— Treat with bisphosphonates (zoledronate single dose preferred)

— Low ALP (unique!), normal/high Ca, low pyridoxal-5-phosphate

— Premature tooth loss, fractures, mimics osteomalacia

— Avoid bisphosphonates — worsen disease; use asfotase alfa

— Mixed: high-turnover (osteitis fibrosa) + low-turnover (adynamic bone) + osteomalacia

— Bone biopsy distinguishes; clinically managed per CKD-MBD guidelines

— Childhood-onset bowing, short stature, high FGF23, low PO₄, normal Ca and 25-OH-D, inappropriately normal 1,25-D

— Treat with phosphate + calcitriol or burosumab

Osteoporosis:

Primary hyperparathyroidism:

Secondary hyperparathyroidism (CKD-MBD):

Tertiary hyperparathyroidism:

Paget disease of bone:

Hypophosphatasia:

Renal osteodystrophy spectrum:

X-linked hypophosphatemia (XLH):

Board pearl: ALP is the great triage tool — high in osteomalacia and Paget, low in hypophosphatasia, normal in osteoporosis.

Key Differentials — Other-Category Causes

— Age >50, shoulder and pelvic girdle pain/stiffness, morning stiffness >45 min

— Markedly elevated ESR/CRP, normal CK, no true weakness

— Dramatic response to prednisone 15–20 mg/d

— Key distinction: stiffness, not weakness; inflammatory markers high; mineral panel normal

— Proximal muscle weakness with elevated CK, aldolase, LDH, AST/ALT

— Skin findings in DM (heliotrope, Gottron); MSA antibodies

— EMG, muscle biopsy

— Proximal weakness, CK often elevated, resolves with discontinuation

— Anti-HMGCR antibody if persistent (immune-mediated necrotizing myopathy)

— Proximal weakness, elevated CK, slowed relaxation phase of reflexes, fatigue, weight gain

— Check TSH

— Widespread pain, tender points, fatigue, sleep disturbance, normal labs and imaging

— No true weakness, no fractures

— Bone pain, fractures, hypercalcemia, anemia, renal failure

— SPEP/UPEP with immunofixation, serum free light chains, skeletal survey or whole-body MRI

— Lytic lesions on imaging; ALP often not elevated (suppressed osteoblasts)

— Breast, prostate, lung, renal, thyroid primaries

— Focal pain, possible hypercalcemia, often elevated ALP

— Bone scan, CT/MRI; biopsy for tissue

— Bone disease + anemia + uremic symptoms

— Overlaps with osteomalacia; manage as CKD-MBD

— Activated macrophages convert 25-OH-D → 1,25-D → hypercalcemia and hypercalciuria with low PTH

— Treat with glucocorticoids; avoid sun and vitamin D supplementation

— Long-term PPI use → hip fracture risk

— Heparin, glucocorticoids, aromatase inhibitors, GnRH agonists: bone loss

— Anticonvulsants, antiretrovirals (tenofovir): osteomalacia mechanism

Polymyalgia rheumatica (PMR):

Polymyositis/dermatomyositis:

Statin-induced myopathy:

Hypothyroid myopathy:

Fibromyalgia:

Multiple myeloma:

Metastatic bone disease:

Chronic kidney disease per se:

Sarcoidosis and granulomatous disease:

Drug-induced osteopathy:

Step 3 management: When proximal weakness is the dominant symptom, the discriminator is CK: normal CK points to osteomalacia, PMR, fibromyalgia; elevated CK points to myositis, statin/hypothyroid myopathy, rhabdomyolysis.

Board pearl: Sarcoidosis is the trap: hypercalcemia with low PTH and high 1,25-D — don't give vitamin D or sunlight!

Secondary Prevention and Long-Term Plan

— General adults: 600 IU/d (IOM RDA); 800 IU/d age >70

— At-risk adults (Endocrine Society): 1,500–2,000 IU/d to maintain 25-OH-D ≥30 ng/mL

— Obesity, malabsorption, anticonvulsants, glucocorticoids: 2–3× standard dose, often 3,000–6,000 IU/d

— Post-bariatric: lifelong 3,000 IU/d minimum + calcium citrate

— 1,000 mg/d adults <50; 1,200 mg/d women >50, men >70

— Prefer dietary sources (dairy, fortified plant milks, leafy greens, fortified cereals, tofu, canned fish with bones)

— Supplement only the gap; excess calcium supplementation linked to cardiovascular and renal stone risk

— Sun exposure: 10–30 min midday, arms/legs, 2–3×/week when feasible (skin-cancer balance)

— Weight-bearing and resistance exercise ≥3×/wk to maintain bone and muscle

— Smoking cessation, alcohol ≤2 drinks/d

— Fall prevention: home safety, vision/hearing optimization, footwear

— Celiac: strict gluten-free diet

— IBD: optimize disease control, supplement aggressively

— Cholestatic liver disease: ursodiol if PBC; fat-soluble vitamin replacement

— Drug-induced: switch anticonvulsant if feasible (levetiracetam less culprit), taper glucocorticoids to minimum

— Post-bariatric: lifelong micronutrient panel annually (D, B12, iron, folate, A, E, K, zinc, copper)

— Bisphosphonate (alendronate, risedronate, zoledronate) if T-score ≤ –2.5, prior fragility fracture, or high FRAX

— Denosumab if renal impairment limits bisphosphonate

— Anabolic (teriparatide, romosozumab) for very high risk

— Always continue vitamin D + calcium as backbone

— DXA at age 65 (women) / 70 (men) or earlier with risk factors (USPSTF)

— FRAX to guide therapy in osteopenia

— Annual fall risk assessment in elders

Maintenance vitamin D:

Maintenance calcium:

Lifestyle:

Treat the root cause:

Concurrent osteoporosis therapy (once vitamin D ≥30 and Ca normal):

Screening to consider:

Step 3 management: A patient with a fragility fracture should leave the hospital with (1) vitamin D + calcium, (2) DXA scheduled, (3) PCP follow-up within 2–4 weeks, (4) PT referral, (5) bone-health specialist referral if complex. Fracture-liaison services reduce re-fracture by ~30%.

Board pearl: Documenting secondary prevention after fragility fracture is a CMS quality measure — Step 3 expects you to order both vitamin D/calcium and an antiresorptive.

Follow-Up, Monitoring, and Counseling

— 2–4 weeks after starting repletion: symptom check, medication adherence, side effects (constipation, GI upset, hypercalcemia symptoms)

— 8–12 weeks: repeat 25-OH-D, Ca, PO₄, PTH, ALP, Cr

— Goal: 25-OH-D ≥30 ng/mL, Ca and PO₄ normal, PTH normalizing, ALP trending down

— If 25-OH-D still <30, repeat 8-week loading course

— 6 months: repeat mineral panel; assess bone pain, weakness, function

— Annually thereafter for at-risk patients; every 2–3 years if stable

— Healing of Looser zones confirms diagnosis and treatment success — can be slow (6–12 months)

— Repeat DXA at 2 years to monitor BMD response

— PT for balance, hip-girdle strengthening, gait training

— OT for home safety, ADL adaptation

— Reassess Timed Up and Go and chair-stand at 3 and 6 months

— Document falls in past 3 months at each visit

— Adherence: explain why both calcium and vitamin D are needed

— Diet: 3 servings dairy/d or equivalent; fatty fish 2×/wk; fortified foods

— Sun: balance against skin cancer; use supplements as primary source for high-risk skin patients

— Falls: remove rugs, install grab bars, night lights, non-slip mats; vision check yearly

— Bone-friendly behaviors: weight-bearing exercise, smoking cessation, limit alcohol/cola

— When to call: tingling around mouth/fingers (hypocalcemia symptoms), polyuria/thirst (hypercalcemia from over-supplementation), new severe focal pain (fracture)

— Med review: warn against unprescribed mega-dose supplements; many OTC products contain >5,000 IU/dose

— Bone-health follow-up after fragility fracture is tracked

— Medicare Annual Wellness Visit is the appropriate venue to incorporate fall-risk and bone-health screening

Follow-up cadence (outpatient family-medicine voice):

Imaging follow-up:

Functional and rehab follow-up:

Counseling topics (testable Step 3 patient-education content):

Quality measures and value-based care:

Step 3 management: If after 12 weeks of compliant high-dose repletion the 25-OH-D fails to rise above 20 ng/mL, think malabsorption — check celiac serology, fecal elastase, review surgical history, and consider switching to calcifediol or parenteral D.

Board pearl: ALP is the best biochemical bellwether of treatment response — it lags by 3–6 months but reliably normalizes with mineralization.

Ethical, Legal, and Patient Safety Considerations

— Post-hip-fracture handoff is a notorious gap: many patients are discharged without vitamin D, calcium, or osteoporosis therapy despite a fragility fracture. Use a fracture-liaison service or explicit checklist

— Medication reconciliation at every transition — vitamin D and calcium are often unintentionally dropped during hospital admissions and SNF transfers

— Written discharge instructions and scheduled follow-up within 2–4 weeks with PCP

— Discuss benefits and risks of antiresorptive therapy (atypical femur fracture ~1/10,000 patient-years, ONJ, GI side effects) vs. fracture risk if untreated

— For elderly with limited life expectancy: weigh number-needed-to-treat against pill burden and falls risk

— Patients have the right to refuse — document discussion

— Suspected elder abuse/neglect in a malnourished, sun-deprived nursing-home resident with severe deficiency and untreated fractures → mandatory report to Adult Protective Services

— Suspected child neglect in untreated nutritional rickets or breastfed infant denied vitamin D supplementation → consider Child Protective Services depending on context and parental capacity

— Cultural/religious considerations (e.g., veiled mothers) require education, not punitive reporting as first step

— Dark-skinned and immigrant patients are systematically under-screened

— Low-income patients may face supplement cost barriers — prescribe vitamin D (covered by most plans) rather than recommend OTC when access is limited

— Use professional interpreters for counseling — never family members for medical history

— High-dose 50,000 IU capsules are weekly — accidental daily dosing causes toxicity. Counsel carefully and write directions explicitly

— Don't co-prescribe thiazides with high-dose vitamin D without monitoring calcium

— Bisphosphonate before vitamin D repletion → severe hypocalcemia; always check 25-OH-D and Ca before starting

— Vitamin D supplementation in unselected populations (VITAL trial) did not reduce cardiovascular events or cancer — counsel patients accordingly; the indication is bone health and documented deficiency, not universal prevention

— Avoid testing/treatment cascades — don't screen asymptomatic low-risk adults (Choosing Wisely)

Transition-of-care safety (high-yield Step 3 theme):

Informed consent and shared decision-making:

Mandatory reporting:

Vulnerable populations and equity:

Patient safety — drug errors:

Research and biostatistics:

Board pearl: A nursing-home resident with a hip fracture, severe vitamin D deficiency, weight loss, and pressure ulcers warrants both medical repletion and an APS referral for possible neglect.

High-Yield Associations and Rapid-Fire Clinical Facts

— Skin (UVB) → cholecalciferol → liver (25-hydroxylase, CYP2R1) → 25-OH-D → kidney (1α-hydroxylase, CYP27B1) → 1,25-(OH)₂-D → catabolism by 24-hydroxylase (CYP24A1)

— Calcium LO, Phosphate LO, Alk Phos HI, PTH HI = nutritional osteomalacia

— Looser zones = pseudofractures of osteomalacia

— Codfish vertebrae = biconcave vertebrae

— Rachitic rosary, Harrison groove, craniotabes = pediatric rickets

— Brown tumors, salt-and-pepper skull = hyperparathyroidism

— Cotton-wool skull = Paget disease

— Superscan = diffuse uptake on bone scan (osteomalacia, metastases)

— 1 mcg = 40 IU vitamin D

— 1,000 mg calcium carbonate = 400 mg elemental Ca

— 1,000 mg calcium citrate = 210 mg elemental Ca

— Elderly, institutionalized, housebound

— Dark skin, veiling, sunscreen use, northern latitude

— Malabsorption: celiac, IBD, post-bariatric, pancreatic insufficiency, cholestasis

— Drug-induced: phenytoin, phenobarbital, carbamazepine, rifampin, glucocorticoids, isoniazid, antiretrovirals

— CKD stage 4–5, dialysis

— Obesity (sequestration), pregnancy/lactation, breastfed infants

— Macrophage 1α-hydroxylase → inappropriate 1,25-D, hypercalcemia, low PTH — sarcoid, TB, fungal, lymphoma

— Treat with glucocorticoids; avoid sun and supplementation

— Small mesenchymal tumors secrete FGF23 → phosphaturia, low PO₄, low 1,25-D

— Diagnose with Ga-68 DOTATATE PET/CT; cure with resection; burosumab if not resectable

— Anticonvulsants/rifampin: CYP24A1 induction → ↑D catabolism

— Tenofovir: proximal tubular toxicity → Fanconi → phosphate wasting

— Aluminum (old phosphate binders, dialysis water): direct mineralization toxicity

— Bisphosphonates (rare): mineralization defect at very high doses

— Fluoride excess: dense but defective bone

Vitamin D activation pathway:

Lab signature mnemonic ("LO-LO-HI-HI"):

Buzzwords on Step 3:

Pharmacologic equivalents:

At-risk groups (memorize):

Granulomatous/lymphoma hypercalcemia:

Tumor-induced osteomalacia (TIO):

Drug-induced osteomalacia mechanisms:

Board pearl: Adynamic bone disease in dialysis = low turnover with low PTH (often from oversuppression with calcimimetics/active D) and low ALP — distinct from osteomalacia and treated by allowing PTH to rise.

Key distinction: Osteomalacia = mineralization defect; osteoporosis = mass defect; Paget = remodeling defect; renal osteodystrophy = mixed.

Board Question Stem Patterns

"72-year-old housebound woman falls and sustains a femoral neck fracture. Labs: Ca 8.0, PO₄ 2.2, ALP 280, PTH 110, 25-OH-D 8 ng/mL. Next best step?"

— Answer: Replete vitamin D and calcium (e.g., ergocalciferol 50,000 IU weekly × 8 weeks plus calcium 1,200 mg/d) before initiating bisphosphonate.

"45-year-old 3 years post Roux-en-Y with diffuse bone pain, proximal weakness, low Ca, low PO₄, high PTH, 25-OH-D 6. Best long-term plan?"

— Answer: High-dose vitamin D (50,000 IU 1–3×/wk) + calcium citrate + annual nutritional panel; consider calcifediol if refractory.

"30-year-old on phenytoin × 10 years with bone pain, low 25-OH-D, high ALP."

— Answer: Higher maintenance vitamin D doses (≥2,000 IU/d) ± switching anticonvulsant; replete with 50,000 IU weekly.

"50-year-old with year of worsening weakness; PO₄ 1.5, normal Ca, 25-OH-D 32, low 1,25-D, high FGF23."

— Answer: Ga-68 DOTATATE PET/CT to localize mesenchymal tumor; surgical resection curative.

"Stage 5 CKD on dialysis with bone pain, PO₄ 6.5, Ca 8.2, PTH 800, 25-OH-D 18."

— Answer: Phosphate binder (sevelamer), active vitamin D analog (paricalcitol), calcimimetic if refractory.

"40-year-old with bilateral hilar adenopathy, Ca 11.5, PO₄ normal, PTH suppressed, 1,25-D elevated."

— Answer: Glucocorticoids; avoid vitamin D and sun exposure — this is hypercalcemia, not osteomalacia.

"Elderly woman with carpopedal spasm, perioral tingling, Ca 6.8, Mg 1.2, QT prolonged."

— Answer: IV calcium gluconate + IV magnesium, then oral repletion with cholecalciferol + calcium.

"Exclusively breastfed 10-month-old, dark-skinned, with bowed legs, rachitic rosary, delayed dentition."

— Answer: Ergocalciferol/cholecalciferol 2,000 IU/d × 6–12 weeks, then 400 IU/d maintenance; supplement mother; reinforce AAP 400 IU/d for all breastfed infants.

"Patient with osteoporosis on DXA, 25-OH-D 12; the resident wants to start alendronate."

— Answer: Replete vitamin D first to avoid severe hypocalcemia.

"Radiograph shows transverse lucent band perpendicular to the medial femoral cortex."

— Answer: Pseudofracture of osteomalacia — order 25-OH-D, mineral panel, PTH.

Pattern 1 — Elderly woman with hip fracture:

Pattern 2 — Post-bariatric patient:

Pattern 3 — Anticonvulsant-induced:

Pattern 4 — Tumor-induced osteomalacia:

Pattern 5 — CKD patient:

Pattern 6 — Sarcoidosis trap:

Pattern 7 — Hypocalcemic tetany:

Pattern 8 — Pediatric rickets:

Pattern 9 — Avoid antiresorptive in untreated deficiency:

Pattern 10 — Looser zone:

Board pearl: When the stem mentions proximal weakness + bone pain + abnormal mineral panel, the diagnosis is osteomalacia 95% of the time on Step 3.

One-Line Recap

Osteomalacia is a defective bone-mineralization disorder of adults — most often from vitamin D deficiency — that classically presents with diffuse bone pain, proximal muscle weakness, fragility fractures, and the lab tetrad of low calcium, low phosphate, high alkaline phosphatase, and high PTH, and is treated by repleting vitamin D and calcium while correcting the underlying cause (malabsorption, drugs, CKD, or phosphate-wasting tumor) before any antiresorptive therapy is initiated.

Recognize: Diffuse bone pain + proximal weakness + waddling gait + fragility fracture, especially in housebound elderly, dark-skinned, post-bariatric, malabsorption, CKD, or anticonvulsant-using patients — confirm with 25-OH-D, Ca, PO₄, ALP, PTH, Mg, urine Ca, and look for Looser zones on plain films.

Replete: Ergocalciferol 50,000 IU weekly × 8 weeks (or cholecalciferol 6,000 IU/d) plus calcium 1,000–1,200 mg elemental/d, with calcitriol if CKD or hypoparathyroidism, calcifediol if severe malabsorption, and aggressive magnesium correction; recheck labs at 8–12 weeks and target 25-OH-D ≥30 ng/mL.

Address root cause: Treat celiac/IBD, adjust anticonvulsants, manage CKD-MBD with phosphate binders and active D analogs, evaluate FGF23 and Ga-68 DOTATATE PET/CT for suspected tumor-induced osteomalacia, and lifelong supplement post-bariatric patients.

Prevent the next fracture: Combine repletion with fall prevention, weight-bearing exercise, DXA screening, and appropriate antiresorptive therapy after mineral parameters are corrected; close transitions-of-care gaps with a fracture-liaison handoff to the PCP within 2–4 weeks of discharge.

Board pearl: The single most testable point — never start a bisphosphonate or denosumab in a patient with unrecognized vitamin D deficiency; correct the deficiency first to avoid life-threatening hypocalcemia, and remember that osteomalacia has an abnormal mineral panel while osteoporosis is biochemically silent.