Endocrine

Hypothyroidism: outpatient management and dose titration

Clinical Overview and When to Suspect Hypothyroidism

— Primary: elevated TSH with low or normal free T4 (overt vs subclinical)

— Central (secondary/tertiary): low/inappropriately normal TSH with low free T4 from pituitary or hypothalamic disease

— Prevalence ~5% overt, ~5% subclinical in US adults; female:male ~8:1

— Peak incidence age 40–60; rises further after age 65

— Hashimoto thyroiditis is the dominant etiology in iodine-sufficient countries; iodine deficiency dominates globally

— Other causes: post-ablative (RAI, thyroidectomy), external beam radiation to neck, drug-induced (amiodarone, lithium, interferon-α, checkpoint inhibitors, tyrosine kinase inhibitors), transient (postpartum, subacute, silent thyroiditis), congenital, infiltrative (hemochromatosis, sarcoid)

— Nonspecific fatigue, cold intolerance, constipation, weight gain, dry skin, menorrhagia, depression, hair thinning, hoarseness, paresthesias, slowed mentation

— New diastolic hypertension, bradycardia, unexplained dyslipidemia (especially elevated LDL), hyponatremia, macrocytic anemia, elevated CK

— Pregnancy with prior thyroid disease, recurrent miscarriage, infertility, postpartum mood disorder

— Statin-associated myalgia that doesn't resolve — check TSH before relabeling as statin intolerance

Definition: Hypothyroidism is a deficiency of circulating thyroid hormone action, most commonly from primary thyroid gland failure (>95% of US cases).

Epidemiology and high-yield risk groups:

When to suspect on a Step 3 outpatient stem:

Screening posture: USPSTF gives insufficient evidence (I statement) for routine screening in non-pregnant asymptomatic adults; ATA endorses case-finding in high-risk groups (age >60, autoimmune disease, prior neck radiation, type 1 DM, family history, amiodarone/lithium).

Board pearl: A middle-aged woman with fatigue, hypercholesterolemia, and unexplained CK elevation has hypothyroidism until proven otherwise — order TSH first, not a lipid panel repeat or muscle biopsy.

Presentation Patterns and Key History

— Cold intolerance, weight gain despite poor appetite, constipation, fatigue, dry coarse skin, hair loss (including lateral third of eyebrows — "Queen Anne sign"), hoarseness, slowed cognition, depression

— Menstrual changes: menorrhagia in younger women, oligomenorrhea later; reduced fertility; galactorrhea from secondary hyperprolactinemia (TRH stimulates prolactin)

— Older adults: often present only with fatigue, falls, cognitive slowing, or new heart failure — "apathetic hypothyroidism"

— New refractory diastolic HTN or sinus bradycardia in an otherwise healthy patient

— Sleep disturbance with obstructive sleep apnea worsened by macroglossia and pharyngeal myxedema

— Carpal tunnel syndrome bilaterally without occupational explanation

— Prior thyroid surgery, radioactive iodine, neck irradiation (Hodgkin lymphoma survivors)

— Medication review: amiodarone, lithium, interferon, immune checkpoint inhibitors (pembrolizumab, nivolumab), tyrosine kinase inhibitors (sunitinib), iodinated contrast within recent weeks

— Recent pregnancy (postpartum thyroiditis 4–8 months post-delivery)

— Family history of autoimmune thyroid disease, type 1 DM, vitiligo, pernicious anemia, celiac, adrenal insufficiency (APS-2)

— Iodine intake — kelp/seaweed supplements (iodine excess can paradoxically cause hypothyroidism via Wolff-Chaikoff escape failure in autoimmune glands)

— Timing of levothyroxine relative to food, coffee, calcium, iron, PPIs, sucralfate, bile acid sequestrants, soy

— Recent GI surgery, celiac, atrophic gastritis

Classic symptom cluster (high specificity, low sensitivity):

Subtle/atypical presentations to anchor on for Step 3:

Targeted history — always ask:

Adherence and absorption history (critical for titration questions):

Key distinction: Symptoms correlate poorly with TSH level — do not adjust therapy by symptoms alone; a patient may "feel hypothyroid" with a normal TSH due to depression, anemia, OSA, or perimenopause. Always re-verify the biochemical diagnosis before chasing residual symptoms with dose escalation.

Physical Exam Findings and Vital Sign Assessment

— Bradycardia (HR often 50s–60s), mild diastolic hypertension from increased SVR, narrow pulse pressure

— Low-grade hypothermia; mild weight gain (usually <10 lb attributable to thyroid itself — large gains suggest other causes)

— Severe presentation (myxedema coma): hypothermia <35°C, hypotension, bradycardia, hypoventilation — admit immediately

— Periorbital and pretibial non-pitting edema (myxedema — glycosaminoglycan deposition)

— Coarse, dry skin; brittle nails; thinning hair; loss of lateral eyebrows

— Yellowish skin tint (carotenemia from impaired conversion)

— Hoarse, slow speech; macroglossia in advanced disease

— Hashimoto: symmetric, firm, rubbery, bumpy ("pebbly") goiter; nontender

— Subacute (de Quervain) thyroiditis: tender, painful gland after viral URI

— Riedel thyroiditis: rock-hard, fixed (IgG4-related, rare)

— Post-surgical or post-ablation: gland atrophic or absent

— Delayed relaxation phase of deep tendon reflexes ("Woltman sign") — classic at the Achilles, highly specific

— Proximal myopathy, elevated CK, Hoffmann syndrome (muscle pseudohypertrophy)

— Bilateral carpal tunnel signs (Tinel, Phalen)

— Cerebellar ataxia in severe cases

Vital signs in the outpatient:

General appearance:

Thyroid exam:

Cardiac: distant heart sounds, possible pericardial effusion (rarely tamponade); S4 from impaired relaxation; mild cardiomegaly

Neuromuscular:

Mental status: psychomotor slowing, depressed affect, impaired memory, occasionally "myxedema madness" with psychosis

Associated autoimmune signs: vitiligo patches, alopecia areata, signs of pernicious anemia (glossitis, posterior column deficits), adrenal insufficiency (hyperpigmentation, orthostasis).

Board pearl: Delayed ankle reflex relaxation + bradycardia + diastolic HTN + dyslipidemia in a fatigued woman = order TSH and free T4 as your single most cost-effective next step on a CCS case.

Diagnostic Workup — Initial Labs

— Most sensitive single test for primary hypothyroidism because of log-linear feedback: small free T4 drop → large TSH rise

— Normal reference range: ~0.4–4.5 mIU/L (lab-specific); age-adjusted upward in elderly (consider up to 6–7 in patients >70)

— TSH high + free T4 low → overt primary hypothyroidism — treat

— TSH high + free T4 normal → subclinical hypothyroidism — treatment depends on degree, age, symptoms, pregnancy plans

— TSH low/normal + free T4 low → central hypothyroidism — evaluate pituitary; do not rely on TSH for titration

— TSH high + free T4 high → assay interference, TSH-secreting adenoma, thyroid hormone resistance, or poor adherence with recent dose binge ("Monday-morning levothyroxine")

— Anti-TPO antibodies: positive in >90% of Hashimoto; supports etiology and predicts progression of subclinical disease (~4%/year to overt if TPO+)

— Anti-thyroglobulin antibodies: less specific

— CBC: normocytic or macrocytic anemia (consider co-existing B12 deficiency from autoimmune gastritis)

— BMP: hyponatremia from impaired free water excretion

— Lipid panel: ↑ LDL, ↑ total cholesterol

— CK: elevated in 30–80%

— LFTs: mild transaminitis possible

— Prolactin: mildly elevated from TRH stimulation

— Palpable nodule or asymmetric goiter → thyroid ultrasound

— Suspected central hypothyroidism → pituitary MRI plus full anterior pituitary panel (AM cortisol, ACTH, LH/FSH, prolactin, IGF-1)

— RAIU scan is not indicated for routine hypothyroidism workup

First-line test: serum TSH (3rd-generation assay).

Interpretation algorithm:

Confirmatory and ancillary labs:

When to image:

Step 3 management: On a CCS, order TSH first; if abnormal, reflex to free T4 and anti-TPO on the same visit to avoid a wasted return appointment. Document the goiter exam and screen for autoimmune comorbidities (HbA1c, B12, vitamin D) given clustering.

Diagnostic Workup — Advanced and Confirmatory Studies

— Biotin (≥5 mg/day, common in hair/nail supplements) causes spuriously low TSH and high free T4 on immunoassays — hold biotin ≥48 hours before retesting

— Heterophile antibodies / macro-TSH: discordant TSH; repeat on different platform or with PEG precipitation

— Nonthyroidal illness ("sick euthyroid"): low T3, low/normal free T4, normal or low TSH during acute illness — do not start levothyroxine in a hospitalized patient based on these labs; recheck after recovery

— Confirm by repeating TSH (and free T4) in 6–8 weeks before labeling and treating — many transient elevations resolve (recovery from illness, thyroiditis phases)

— Check anti-TPO to estimate progression risk

— Free T4 is the gold standard for diagnosis and titration — TSH is unreliable

— Always rule out and treat secondary adrenal insufficiency first with AM cortisol ± ACTH stim before starting levothyroxine (levothyroxine accelerates cortisol clearance → adrenal crisis)

— Pituitary MRI; visual fields if mass suspected

— Classic triphasic course: thyrotoxic phase (1–6 months postpartum, low TSH, often missed), hypothyroid phase (4–8 months), recovery (most by 12 months)

— Anti-TPO often positive; low RAIU during thyrotoxic phase distinguishes from Graves (contraindicated if breastfeeding — use clinical context instead)

— Heterogeneous hypoechoic parenchyma, pseudonodules, increased vascularity

— FNA only for discrete nodules ≥1 cm or suspicious features

When the basic panel doesn't fit, think interference and atypical patterns:

Subclinical hypothyroidism workup:

Central hypothyroidism evaluation:

Postpartum thyroiditis workup:

Thyroid ultrasound features in Hashimoto:

Key distinction: Subclinical hypothyroidism vs assay artifact — always repeat in 6–8 weeks and screen for biotin use before committing a young patient to lifelong therapy. Mislabeling drives unnecessary lifelong prescriptions, a high-yield Step 3 patient-safety theme.

Risk Stratification and Treatment Decision Logic

— TSH ≥10 mIU/L: treat — clear cardiovascular and progression benefit; reduces CHD events especially in patients <65

— TSH 7–9.9 mIU/L: treat if age <70, symptomatic, anti-TPO positive, goiter, dyslipidemia, or pregnancy/planning

— TSH 4.5–6.9 mIU/L in age <65: consider trial if symptomatic and anti-TPO positive; otherwise observe and recheck in 6 months

— TSH 4.5–6.9 mIU/L in age ≥70: do not treat — observation preferred; treatment increases risk of AF, osteoporosis, and may not improve symptoms (TRUST trial)

— Treat all overt hypothyroidism

— Treat subclinical if TSH > trimester-specific upper limit (commonly >4.0 mIU/L) and TPO positive, or TSH >10 regardless

— Preconception goal TSH <2.5 in known hypothyroid patients

— Healthy adult <60, no CAD: full replacement ~1.6 mcg/kg/day of ideal body weight

— Age ≥60 or known CAD: start 25–50 mcg/day and titrate slowly (avoid precipitating angina/MI/arrhythmia)

— Subclinical: lower, 25–75 mcg/day depending on TSH

— Post-thyroidectomy for cancer: suppression dosing per ATA risk category (separate algorithm)

Overt primary hypothyroidism (TSH high, free T4 low): treat all patients regardless of symptoms.

Subclinical hypothyroidism (TSH high, free T4 normal) — stratify by TSH level, age, and context:

Pregnancy and preconception — lower thresholds:

Always exclude/treat adrenal insufficiency before starting levothyroxine if any clinical suspicion (hypotension, hyperpigmentation, hyponatremia, fatigue out of proportion, known panhypopituitarism).

Choose the right starting dose:

CCS pearl: Before writing the levothyroxine order on a CCS hypothyroid case in an elderly patient with chest pain history, order EKG and consider stress testing, and start at 25 mcg/day with a 6-week TSH recheck — full replacement up front can unmask ischemia and is a classic distractor.

Pharmacotherapy — Levothyroxine Initiation and Titration

— Preferred over desiccated thyroid extract (Armour) and T4/T3 combinations: stable pharmacokinetics, predictable TSH response, lower arrhythmia risk

— Half-life ~7 days → steady state in 6 weeks → that's your recheck interval

— Young, healthy, overt: 1.6 mcg/kg/day (ideal body weight) — typical 100–125 mcg

— Elderly or CAD: 25–50 mcg/day, increase by 12.5–25 mcg every 6 weeks

— Subclinical: 25–75 mcg/day

— Pregnancy with pre-existing hypothyroidism: increase dose by ~30% as soon as pregnancy is confirmed (or "two extra pills per week")

— Take on an empty stomach, 30–60 minutes before breakfast, with water only

— Alternative: at bedtime, ≥3 hours after last meal

— Separate from calcium, iron, PPIs, antacids, sucralfate, bile acid sequestrants, soy, high-fiber supplements by ≥4 hours

— Be consistent with brand vs generic — switching products requires recheck of TSH in 6 weeks

— Recheck TSH at 6 weeks after any dose change (or free T4 if central hypothyroidism)

— Adjust in 12.5–25 mcg increments

— Goal TSH:

— General adult: 0.4–4.0 mIU/L (mid-normal ~1–2.5)

— Pregnancy: trimester-specific, generally <2.5 (1st), <3.0 (2nd/3rd)

— Elderly ≥70: upper goal 4–6 acceptable

— Thyroid cancer post-thyroidectomy: suppressed per risk stratification

First-line agent: levothyroxine (LT4) — synthetic T4, peripherally deiodinated to active T3.

Starting dose by population:

Administration counseling — high-yield Step 3 outpatient teaching:

Titration rules:

Once stable: recheck TSH at 6 months, then annually, or sooner with symptom change, pregnancy, weight change >10%, or new interacting drug.

Board pearl: New levothyroxine malabsorption in a previously stable patient → ask about PPIs, calcium/iron supplements, recent bariatric surgery, or new celiac disease before escalating dose. Treating the cause beats chasing higher mcg.

Expanded Pharmacology — Special Formulations and Drug Interactions

— Tablets (Synthroid, Levoxyl, generic): cheapest, food-sensitive

— Soft-gel capsules (Tirosint) and oral solution: bypass gastric pH dependence — useful in PPI users, post-bariatric, celiac, or persistent absorption issues

— IV levothyroxine: reserved for myxedema coma or NPO patients; IV dose ~75% of oral dose

— Not routinely recommended; consider in select symptomatic patients with normal TSH on LT4 alone and no other explanation

— Short half-life → fluctuating levels, palpitations, anxiety, AF risk

— Desiccated thyroid extract: non-physiologic T4:T3 ratio (~4:1 vs human 14:1), variable potency — avoid as first-line per ATA

— Decrease absorption: calcium carbonate, ferrous sulfate, aluminum/magnesium antacids, sucralfate, bile acid sequestrants (cholestyramine, colesevelam), phosphate binders, raloxifene, ciprofloxacin, soy, coffee, fiber — separate by 4 hours

— Increase requirement (induce metabolism or binding): estrogens (OCPs, HRT, pregnancy) ↑ TBG, rifampin, phenytoin, carbamazepine, phenobarbital, sertraline, tyrosine kinase inhibitors (imatinib, sunitinib)

— Acid suppression (PPIs, H2 blockers): reduce absorption of tablets (not soft-gel/solution)

— Amiodarone: complex — can cause both hypo- and hyperthyroidism

— Starting estrogen-containing contraceptive or HRT → recheck TSH in 6 weeks, expect dose increase ~10–25%

— Starting/stopping enzyme inducer → recheck TSH in 6 weeks

— Initiating PPI in patient with previously stable TSH → recheck and counsel on spacing

— Don't switch among brands/generics without 6-week recheck

— Don't dose-titrate using T3 levels in routine primary hypothyroidism

— Don't add T3 reflexively for "fatigue despite normal TSH" — evaluate depression, OSA, anemia, vitamin D, B12, sleep

Levothyroxine formulations:

Liothyronine (T3) and combination therapy:

Major drug interactions — memorize for exam:

Monitoring during interacting therapy:

What NOT to do:

Step 3 management: A patient newly started on estrogen-containing OCPs with rising TSH needs a dose increase of levothyroxine, not a new diagnosis — recognize the TBG effect.

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher TSH reference range with age — TSH up to 6–7 mIU/L may be physiologic in patients >80; avoid over-treatment

— Increased risk of treatment harms: atrial fibrillation, osteoporosis/fractures, accelerated bone loss, precipitation of angina/MI

— TRUST trial (NEJM 2017): no symptomatic benefit from levothyroxine in adults ≥65 with subclinical hypothyroidism (mean TSH ~6); supports observation

— Start low, go slow: 12.5–25 mcg/day; increase by 12.5–25 mcg every 6 weeks

— Target higher TSH goal (4–6) in frail patients

— Screen for CAD before initiating; baseline EKG reasonable

— Watch for paradoxical worsening of cognition or function with overshoot — iatrogenic subclinical hyperthyroidism is common and harmful

— If angina worsens on LT4, reduce dose and evaluate for ischemia rather than push to euthyroid

— Goal: lowest dose that resolves overt symptoms; tolerate mildly elevated TSH if necessary

— No dose adjustment required for levothyroxine itself

— Hypothyroidism can falsely lower eGFR estimates (reduced muscle mass, ↓ creatinine clearance via renal hemodynamics); treating may improve eGFR

— Nephrotic syndrome: urinary loss of TBG-bound T4 may increase LT4 requirements

— No specific dose adjustment; monitor TSH

— Cirrhosis can mildly alter TBG and deiodinase activity but rarely changes dosing

— Roux-en-Y and sleeve gastrectomy can reduce absorption; consider liquid or soft-gel formulation and recheck TSH at 6 weeks post-op and after weight stabilization

Elderly (≥65–70):

Cardiac disease:

Renal impairment:

Hepatic impairment:

Post-bariatric surgery:

Board pearl: In an 82-year-old with TSH 6.2, free T4 normal, no symptoms — the right answer is observe and repeat in 6 months, not initiate levothyroxine. Over-treatment in elderly is a top patient-safety pitfall on Step 3.

Special Populations — Pregnancy, Postpartum, and Pediatric Crossover

— Goal preconception TSH <2.5 mIU/L in known hypothyroid women

— Counsel that LT4 requirement rises ~20–50% in pregnancy due to ↑ TBG (estrogen), placental deiodinase, fetal demand

— Immediately increase dose by ~30% — practical method: take 2 extra tablets per week (9 doses/7 days)

— Check TSH every 4 weeks through 20 weeks, then at least once at 26–32 weeks

— Trimester-specific TSH goals: 1st trimester <2.5, 2nd/3rd <3.0 (or institution-specific)

— Overt hypothyroidism: always treat — untreated risks include miscarriage, preeclampsia, preterm birth, placental abruption, low birth weight, impaired offspring neurocognitive development

— Subclinical hypothyroidism: treat if TSH > trimester upper limit (commonly 4.0) and TPO positive, or TSH >10 regardless of TPO

— Isolated hypothyroxinemia: routine LT4 not recommended

— Return to pre-pregnancy dose immediately after delivery; recheck TSH at 6 weeks

— Watch for postpartum thyroiditis in new mothers: triphasic; hypothyroid phase 4–8 months postpartum; treat symptomatic hypothyroidism with LT4 for 6–12 months, then attempt withdrawal — many recover, but ~20% become permanently hypothyroid; lifelong annual TSH screening recommended

— Universal newborn screening; treat within 2 weeks of birth to prevent intellectual disability

— Dose ~10–15 mcg/kg/day initially

Pre-pregnancy and conception planning:

Confirmed pregnancy in known hypothyroidism:

New diagnosis in pregnancy:

Postpartum:

Lactation: Levothyroxine is safe in breastfeeding.

Congenital hypothyroidism (pediatric crossover for Step 3):

Adolescent/young adult Hashimoto: counsel about future pregnancy planning and pre-conception TSH optimization.

Step 3 management: A patient on stable LT4 reports a positive home pregnancy test — your first order is to increase LT4 by ~30% empirically and draw TSH/free T4 the same week, then recheck TSH every 4 weeks. Don't wait for the OB visit.

Complications and Adverse Outcomes

— Cardiovascular: atherogenic dyslipidemia (↑ LDL, ↑ Lp(a)), accelerated atherosclerosis, diastolic HTN, pericardial effusion, reduced cardiac output, worsened heart failure

— Neuropsychiatric: depression, cognitive impairment, "myxedema madness," cerebellar ataxia

— Hematologic: anemia (normocytic, macrocytic with B12 deficiency, or microcytic with menorrhagia-driven iron loss)

— Reproductive: infertility, miscarriage, menstrual irregularity, galactorrhea

— Musculoskeletal: myopathy, elevated CK, carpal tunnel, Hoffmann syndrome

— Metabolic: hyponatremia (SIADH-like), hypoglycemia (often combined with adrenal insufficiency in APS)

— Severe: myxedema coma — hypothermia, bradycardia, hypoventilation, hyponatremia, altered mental status; mortality 20–40%; triggered by infection, cold, sedatives, surgery, MI

— Atrial fibrillation — 3-fold increased risk with suppressed TSH, especially age >60

— Osteoporosis and fragility fractures, particularly postmenopausal women

— Anxiety, tremor, insomnia, palpitations, heat intolerance

— Worsening angina, ischemia in CAD patients

— Increased CHD events in untreated subclinical hypothyroidism with TSH ≥10, especially in younger patients

— Cognitive trajectory: treatment of overt disease improves cognition; benefit in subclinical disease is modest at best

— Spontaneous abortion, preeclampsia, gestational HTN, placental abruption, preterm delivery, low birth weight, neonatal respiratory distress, impaired offspring IQ

Complications of undertreated or untreated hypothyroidism:

Complications of over-treatment (iatrogenic thyrotoxicosis):

Long-term associations:

Pregnancy-specific complications of inadequate treatment:

Myxedema coma management (CCS): admit to ICU, IV levothyroxine loading (200–400 mcg) then maintenance, IV hydrocortisone 100 mg q8h (until adrenal insufficiency excluded), passive rewarming, treat precipitant, ventilatory support.

Board pearl: A postmenopausal woman on LT4 with new AF and suppressed TSH — first move is reduce her LT4 dose before initiating rate/rhythm control workup; iatrogenic thyrotoxicosis is reversible and a frequent miss.

When to Escalate — Consult, Inpatient, or Emergent Care

— Suspected or confirmed central hypothyroidism — needs full pituitary workup and MRI

— Pregnancy with new diagnosis, unstable control, or thyroid cancer history (some practices co-manage)

— Persistent symptoms despite biochemically euthyroid state on adequate LT4

— Suspected assay interference (biotin, heterophile, macro-TSH) with persistently discordant labs

— Thyroid nodules ≥1 cm or suspicious sonographic features → ultrasound and FNA referral

— Difficult titration: malabsorption syndromes, post-bariatric, refractory subclinical disease

— Suspected TSH-secreting pituitary adenoma (TSH high, free T4 high)

— Hypothyroidism in thyroid cancer survivors (suppression dosing)

— Drug-induced thyroid dysfunction on amiodarone, lithium, immune checkpoint inhibitors, interferon

— Pediatric or adolescent hypothyroidism

— Myxedema coma: altered mental status, hypothermia, bradycardia, hypoventilation — ICU

— Severe hyponatremia, symptomatic bradyarrhythmia, large pericardial effusion with tamponade physiology

— New chest pain or unstable angina precipitated by LT4 initiation

— Suspected adrenal crisis co-presenting with hypothyroidism

— Any patient discharged on a new or up-titrated LT4 must have a documented 6-week TSH follow-up appointment before leaving — common Step 3 patient-safety stem

— Bariatric surgery, GI surgery, or new PPI/calcium prescriptions on existing LT4 patients trigger 6-week recheck

— Pregnancy confirmation triggers same-day dose adjustment and 4-week recheck

— Stable hypothyroidism is appropriately managed long-term in primary care; endocrinology referral for complex or refractory cases preserves access

Refer to endocrinology when:

Admit (or send to ED) when:

Transition-of-care safety nets:

Co-management with primary care:

CCS pearl: On a CCS case with hypothyroid symptoms plus orthostatic hypotension, hyperpigmentation, or hyponatremia, your first order is AM cortisol and IV hydrocortisone empirically before levothyroxine — initiating LT4 in undiagnosed Addison's can precipitate adrenal crisis. This sequence error is heavily tested.

Key Differentials — Other Causes of an Elevated TSH

— Recovery phase of nonthyroidal illness: TSH rebounds to mildly elevated (5–20) after acute hospitalization or critical illness

— Subacute (de Quervain) thyroiditis: post-viral painful goiter, initially thyrotoxic then hypothyroid, then recovery — most patients return to euthyroid

— Silent and postpartum thyroiditis: painless, autoimmune, transient hypothyroid phase

— Drug-induced transient hypothyroidism: amiodarone (early), iodinated contrast, lithium initiation

— Hashimoto thyroiditis — most common; TPO antibodies positive

— Post-ablative: prior RAI for Graves or thyroidectomy

— External beam radiation to neck (Hodgkin lymphoma, head/neck cancer survivors) — screen annually for life

— Drug-induced chronic: amiodarone (chronic Wolff-Chaikoff failure), lithium (blocks hormone release), interferon-α, immune checkpoint inhibitors (anti-PD-1, anti-CTLA-4 — increasingly common cause), tyrosine kinase inhibitors

— Infiltrative: Riedel thyroiditis (IgG4-related), hemochromatosis, sarcoidosis, amyloidosis

— Iodine deficiency (rare in US; consider in immigrants, restrictive diets)

— Iodine excess in susceptible glands (kelp, povidone-iodine, contrast)

— Congenital disorders surfacing in adults (rare)

— Biotin supplements

— Heterophile antibodies

— Macro-TSH (biologically inactive complex)

— Recent recovery from suppression (after stopping steroids, dopamine, or thyrotoxicosis treatment)

Transient TSH elevation (must repeat in 6–8 weeks before treating):

Persistent primary hypothyroidism etiologies:

Assay artifacts mimicking hypothyroidism:

TSH-resistance syndromes: very rare; persistent high TSH with normal free T4 and no antibodies, often familial.

Key distinction: Painful goiter + elevated ESR + recent URI = subacute thyroiditis — supportive care (NSAIDs, beta-blockers in thyrotoxic phase), no LT4 unless symptomatic hypothyroid phase, expect resolution in 6–12 months. Don't commit to lifelong LT4.

Key Differentials — Conditions That Mimic Hypothyroidism Symptomatically

— Fatigue, weight gain, cognitive slowing, low libido overlap heavily

— Always check TSH at depression diagnosis, but normal TSH means treat the depression — don't add LT4 to "boost mood"

— Daytime fatigue, weight gain, morning headache, hypertension, depression

— Often coexists with hypothyroidism (macroglossia, pharyngeal myxedema)

— Screen with STOP-BANG; obtain polysomnography

— Fatigue, dyspnea on exertion, cognitive haze; check CBC and iron studies

— Fatigue, weight changes, hyponatremia, hypotension — must be excluded before LT4 in suspect cases

— Beta-blockers (fatigue, bradycardia)

— Statins (myalgia, CK elevation)

— Opioids (constipation, fatigue, cognitive slowing)

— Antipsychotics (weight gain, sedation)

Depression and major depressive disorder:

Obstructive sleep apnea:

Anemia (iron deficiency, B12 deficiency, chronic disease):

Adrenal insufficiency (primary or secondary):

Chronic kidney disease and uremia: fatigue, edema, cognitive slowing

Heart failure: fatigue, edema, dyspnea — overlapping but with pulmonary findings

Menopause/perimenopause: fatigue, weight gain, mood changes, sleep disturbance, hair thinning — hormonal mimic

Nutritional/lifestyle: poor sleep, sedentary lifestyle, alcohol use disorder, vitamin D deficiency

Medication side effects mimicking hypothyroid symptoms:

Fibromyalgia and chronic fatigue syndrome: diagnosis of exclusion; do not over-attribute persistent fatigue to subtly abnormal TSH within normal range.

Celiac disease and other malabsorption: fatigue, anemia, weight changes — and causes refractory LT4 absorption — screen with tTG-IgA in patients needing escalating doses without explanation

Pseudohypothyroidism (T4 binding alterations): estrogen, pregnancy, nephrotic syndrome alter TBG and total T4 but not free T4 — check free T4, not total

Board pearl: Patient on stable LT4 with normal TSH but persistent fatigue — work up depression, OSA, anemia, vitamin D, B12, and celiac before raising the LT4 dose or adding T3. Step 3 frequently tests resisting unnecessary thyroid intensification.

Long-Term Plan and Secondary Prevention

— Most overt primary hypothyroidism is permanent — counsel that LT4 is lifelong

— Exceptions: postpartum/silent/subacute thyroiditis (often transient), amiodarone-induced (may resolve with drug withdrawal), checkpoint-inhibitor-induced (often permanent)

— Document need for annual TSH in stable patients

— Recheck lipids 6–12 months after achieving euthyroid state — many LDL elevations normalize and avoid unnecessary statin

— Standard ASCVD risk assessment with pooled cohort equations once euthyroid

— Manage HTN, diabetes, smoking cessation aggressively — hypothyroidism alone is not a separate ASCVD risk category but contributes

— Avoid TSH suppression unless required for thyroid cancer

— Postmenopausal women: ensure adequate calcium (1200 mg/day) and vitamin D (800–1000 IU); DEXA per USPSTF (≥65, or younger high-risk)

— Increased risk of type 1 DM, celiac, pernicious anemia, vitiligo, Addison's, primary ovarian insufficiency (APS-2)

— Reasonable to check B12 and HbA1c periodically; symptom-directed otherwise

— Screen for celiac if persistent absorption problems or new GI symptoms

— Pill-timing routine (empty stomach, morning, separated from coffee/calcium/iron)

— Bring medication list and supplements to every visit

— Don't switch generic ↔ brand without notifying clinician

— Pregnancy: contact clinician as soon as pregnancy is confirmed — immediate dose increase

— Bring up any new medications (especially PPIs, OCPs, iron, calcium)

Lifelong therapy expectations:

Cardiovascular secondary prevention overlay:

Bone health:

Autoimmune surveillance in Hashimoto patients:

Patient self-management counseling:

Vaccinations and preventive care: standard for age — no thyroid-specific vaccine considerations.

Step 3 management: A 50-year-old newly euthyroid Hashimoto patient with LDL 165 on initial labs — repeat lipids in 6–12 months after TSH normalizes before deciding on a statin; up to 30% of LDL elevation may resolve, sparing unnecessary lifelong therapy.

Follow-Up, Monitoring, and Counseling Cadence

— TSH at 6 weeks after starting LT4 or after any dose change

— Adjust by 12.5–25 mcg as needed; repeat in another 6 weeks

— Free T4 monitoring instead of TSH for central hypothyroidism, recent overt thyrotoxicosis (TSH lags), or pregnancy if discordant

— TSH every 6 months for 1 year, then annually

— Repeat sooner with: pregnancy, weight change >10%, new interacting medication (estrogens, PPI, iron, calcium, anticonvulsants), GI surgery, new symptoms, change in formulation/brand

— TSH (and free T4 if indicated)

— Symptom review: energy, weight, cold intolerance, bowel habits, mood, menstrual pattern

— Medication reconciliation, adherence assessment, supplement use

— Blood pressure, weight, heart rate

— Lipid panel annually until stable; less frequent thereafter

— Reinforce morning empty-stomach dosing and spacing from interactions

— Pregnancy planning conversation in women of reproductive age — preconception TSH <2.5

— Bone health and avoidance of over-suppression in elderly/postmenopausal

— Smoking cessation (smoking worsens autoimmune thyroid disease)

— Exercise improves fatigue and lipid profile once euthyroid

— Adequate sleep, weight management — but counsel realistic expectations: most patients lose only modest weight on LT4 because hypothyroidism alone rarely accounts for >5–10 lb

— ICD-10 E03.9 (primary hypothyroidism, unspecified), E06.3 (Hashimoto), E89.0 (post-procedural)

— Quality measures: TSH monitoring frequency, statin appropriateness, pregnancy preconception counseling

Initiation phase:

Maintenance phase (stable, on goal):

Targets to document at each visit:

Counseling at every encounter (high-yield Step 3 ambulatory tasks):

Rehab/lifestyle:

Documentation/coding for value-based care:

Board pearl: 6 weeks is the magic number for every titration recheck — burn it in. Patients calling at 2–3 weeks asking to recheck "because they don't feel better yet" should be reassured and rescheduled to 6 weeks; premature labs lead to over-titration.

Ethical, Legal, and Patient Safety Considerations

— Transition of care after hospitalization: patients discharged on new LT4 (especially post-thyroidectomy, after myxedema coma, or new diagnosis during admission) need a documented PCP appointment with TSH check at 6 weeks — failure is a common safety event

— Medication reconciliation: levothyroxine is a top medication for inadvertent omission errors during hospital admission; verify timing relative to tube feeds, calcium, iron, sucralfate, PPIs in inpatients

— Tube-fed patients: crush LT4, hold feeds 1 hour before and after, or use oral solution/soft-gel formulation

— Generic substitution: any pharmacy-level substitution requires 6-week TSH recheck — counsel patient to notify clinician

— Look-alike/sound-alike risk: levothyroxine doses (25, 50, 75, 88, 100, 112, 125 mcg) — verify exact strength on every refill; color-coded by manufacturer

— Subclinical hypothyroidism in elderly: discuss equipoise — TRUST trial data show no symptomatic benefit; document shared decision-making before initiating lifelong therapy

— T3/combination therapy requests: counsel about lack of evidence, AF/bone risks, and document discussion

— Pregnancy: explain teratogenic risk of untreated hypothyroidism (neurocognitive harm to fetus) — treatment is strongly indicated, not optional

— Newborn screening for congenital hypothyroidism is mandated in all US states — clinicians must follow up positive screens within 1–2 weeks

— Counsel against unregulated "thyroid support" supplements containing undisclosed T3/T4 — cause iatrogenic thyrotoxicosis; document warning

— Compounded thyroid preparations: discourage due to variable potency

— Generic LT4 is low-cost and on $4 lists — affordability rarely a barrier; verify access for uninsured patients

— Counsel about consistent supply to avoid gaps; hypothyroid relapse develops over weeks

Patient safety — high-frequency Step 3 themes:

Informed consent edge cases:

Mandatory reporting and public health:

Pharmacovigilance:

Health equity and access:

Step 3 management: A nursing-home patient is admitted with myxedema coma after 3 weeks without LT4 following discharge from another facility — this is a transition-of-care patient safety event. Required actions: immediate ICU-level treatment, root-cause analysis, structured discharge medication reconciliation, and prescription synchronization for future. Document and report per institutional safety policy.

High-Yield Associations and Rapid-Fire Facts

— Anti-TPO and anti-thyroglobulin antibodies

— Lymphocytic infiltration with Hürthle (Askanazy) cells and germinal centers on histology

— Associated with primary thyroid lymphoma (rare but classic association — rapidly enlarging goiter in known Hashimoto patient → biopsy urgently)

— HLA-DR3, DR5 associations

— APS-1 (AIRE mutation): chronic mucocutaneous candidiasis, hypoparathyroidism, adrenal insufficiency (pediatric)

— APS-2 (Schmidt syndrome): Addison's + autoimmune thyroid disease + type 1 DM (adult women, HLA-DR3/DR4)

— Amiodarone, Lithium, Interferon, Checkpoint inhibitors, TKIs → "ALICT"

— TSH preconception <2.5; 1st trimester <2.5; 2nd/3rd <3.0

— Increase dose by 30% on positive pregnancy test

— Check every 4 weeks until 20 weeks, then once at 26–32 weeks

— Full replacement: 1.6 mcg/kg/day IBW

— Elderly/CAD start: 25–50 mcg/day

— IV : oral conversion ~ 75%

— Time to steady state: 6 weeks (= recheck interval)

— Biotin → falsely low TSH, falsely high free T4 (mimics hyperthyroidism)

— Hold biotin ≥48 hours before testing

— Pregnancy increases TBG → total T4 up, free T4 unchanged

— Estrogens, nephrotic syndrome, OCPs → alter TBG

— Untreated overt: diastolic HTN, bradycardia, pericardial effusion

— Over-treatment: AF, osteoporosis

Hashimoto thyroiditis (autoimmune):

Autoimmune polyglandular syndromes:

Drug-induced hypothyroidism quick recall:

Pregnancy numbers:

Dose ballpark:

Lab pearls:

Cardiac:

Cholesterol: hypothyroidism is a secondary cause of hypercholesterolemia — always check TSH before initiating statin in new dyslipidemia

Pediatric crossover: congenital hypothyroidism — treat within 2 weeks to preserve IQ

Myxedema coma triad: hypothermia + altered mentation + precipitating event (infection, cold, sedatives)

Board pearl: Rapidly enlarging firm thyroid in a longstanding Hashimoto patient → think primary thyroid B-cell lymphoma (MALT) — urgent core biopsy, not observation.

Board Question Stem Patterns

— 45-year-old woman with fatigue, weight gain, constipation, menorrhagia, diastolic HTN, delayed reflex relaxation. TSH 28, free T4 low.

— Answer: start levothyroxine 1.6 mcg/kg/day, recheck TSH in 6 weeks. Check anti-TPO for documentation.

— 78-year-old, mild fatigue, TSH 6.2, free T4 normal, no goiter, asymptomatic. — Observe and repeat TSH in 6 months (TRUST trial). Treatment is wrong answer.

— 32-year-old on stable LT4, TSH 3.1, plans pregnancy. — Increase LT4 to target TSH <2.5 preconception; once pregnant, increase dose ~30% immediately and check TSH every 4 weeks.

— Stable LT4 patient with positive home pregnancy test. — Increase dose by ~30% (extra 2 pills/week) and check TSH/free T4 within 1–2 weeks; recheck every 4 weeks.

— Stable LT4 patient starts OCPs or HRT, TSH rises. — Increase LT4 dose (TBG effect); recheck in 6 weeks. Same logic for pregnancy or HRT initiation.

— Patient on stable LT4 starts PPI or calcium, TSH climbs. — Counsel 4-hour separation (or switch to soft-gel/liquid LT4); recheck in 6 weeks.

— Older woman on LT4 with new AF, palpitations, suppressed TSH. — Reduce LT4 dose; consider rate control; evaluate stroke risk (CHA₂DS₂-VASc).

— Patient post-pituitary surgery with low free T4, normal TSH. — Treat with LT4 dosed to free T4 target; rule out adrenal insufficiency first and give glucocorticoid before LT4.

— Woman 5 months postpartum, fatigue, TSH 18, free T4 low. — Likely transient; treat symptomatic patients with LT4 6–12 months, then attempt withdrawal with TSH monitoring.

— Elderly nursing-home patient, hypothermic, altered, bradycardic, recent infection. — ICU admission, IV levothyroxine load, IV hydrocortisone, treat precipitant, passive rewarming.

Stem 1 — Classic Hashimoto presentation:

Stem 2 — Elderly with subclinical hypothyroidism:

Stem 3 — Pregnancy planning:

Stem 4 — Recently pregnant patient:

Stem 5 — Drug interaction:

Stem 6 — Absorption issue:

Stem 7 — Iatrogenic thyrotoxicosis:

Stem 8 — Central hypothyroidism:

Stem 9 — Postpartum thyroiditis:

Stem 10 — Myxedema coma:

Board pearl: When the stem describes a stable patient with new TSH derangement after starting a new drug, the answer is almost always "adjust LT4 dose to compensate," not "switch drugs" or "stop LT4." Pattern recognition wins.

One-Line Recap

Hypothyroidism in the outpatient setting is treated with weight-based levothyroxine taken on an empty stomach, titrated by TSH every 6 weeks to a goal of 0.4–4.0 (lower in pregnancy, higher in the elderly), with vigilant attention to drug interactions, pregnancy adjustments, and avoidance of over-treatment.

Diagnose: TSH first; if abnormal, add free T4 and anti-TPO. Repeat at 6–8 weeks before labeling subclinical disease. Exclude assay interference (biotin) and adrenal insufficiency before initiating therapy in central or atypical cases.

Dose: 1.6 mcg/kg/day for healthy adults; 25–50 mcg/day in elderly or CAD; recheck TSH every 6 weeks after any change; annual TSH once stable. Increase by ~30% immediately on confirmed pregnancy.

Titrate by context: treat all overt disease; treat subclinical if TSH ≥10, symptomatic with TPO+, pregnant/planning, or progressive — observe in elderly with TSH <7 (TRUST). Goal in pregnancy: <2.5 (1st trimester), <3.0 (2nd/3rd).

Watch for traps: new PPI/calcium/iron/estrogen → expect dose increase; new AF or osteoporosis → suspect over-treatment, reduce dose; persistent fatigue with normal TSH → evaluate depression, OSA, anemia, B12, celiac — don't reflexively escalate LT4 or add T3.

Patient safety: lifelong therapy + consistent formulation + morning empty-stomach dosing + scheduled 6-week post-change TSH + pregnancy-trigger plan + transition-of-care medication reconciliation = the durable Step 3 framework for hypothyroidism management.