Skin & Subcutaneous Tissue

Psoriatic arthritis: recognition and screening

Clinical Overview and When to Suspect Psoriatic Arthritis

— Adult with known psoriasis reporting new joint pain, morning stiffness >30 minutes, or heel pain

— Asymmetric oligoarthritis (≤4 joints), particularly involving DIP joints

— Dactylitis ("sausage digit") of a finger or toe

— Enthesitis at Achilles or plantar fascia insertion

— Inflammatory low back pain (improves with activity, worsens with rest) in a young/middle-aged adult

— New nail pitting, onycholysis, or oil-drop discoloration with joint symptoms

— Unexplained uveitis or IBD in a patient with skin plaques

Board pearl: Any patient with psoriasis plus inflammatory musculoskeletal symptoms (stiffness >30 min, improves with activity, swelling, nail changes, or enthesitis) should be screened with a tool like PEST and referred to rheumatology — do not wait for radiographic erosions to act.

Psoriatic arthritis (PsA) is a chronic, immune-mediated inflammatory arthritis belonging to the seronegative spondyloarthritis (SpA) family, occurring in roughly 20–30% of patients with cutaneous psoriasis.

Onset typically age 30–50, with equal sex distribution overall (axial-predominant disease is more common in men, peripheral polyarthritis in women).

In ~70% of patients, skin psoriasis precedes joint disease by an average of 7–10 years; in ~15% they appear simultaneously; in ~15% arthritis precedes skin findings (sine psoriasis presentation) — often missed without scalp, umbilicus, gluteal cleft, and nail inspection.

When to suspect in a Step 3 outpatient setting:

Annual screening of all psoriasis patients is recommended (NPF, EULAR, GRAPPA) using validated tools (PEST, PsAID, ToPAS) — primary care often initiates this.

Delayed diagnosis (>6 months from symptom onset) is associated with worse radiographic damage, functional impairment, and lower remission rates — early recognition changes long-term outcomes.

Presentation Patterns and Key History

— Asymmetric oligoarthritis (~30–50%): few large/small joints, often lower extremity

— Symmetric polyarthritis (~30–40%): mimics RA but typically RF/CCP negative and includes DIPs

— Distal interphalangeal (DIP)–predominant (~5–10%): strongly linked to nail disease

— Axial/spondylitic (~5–20%): inflammatory back pain, sacroiliitis, often asymmetric

— Arthritis mutilans (<5%): destructive "pencil-in-cup," telescoping digits

— Inflammatory rhythm: morning stiffness >30 min, improves with movement, nocturnal awakening (especially second half of night for axial disease)

— Dactylitis history: "whole finger or toe swelled up like a sausage for weeks"

— Enthesitis: heel pain on first steps in the morning, lateral epicondyle, iliac crest pain

— Skin/nail review: scalp itch, gluteal cleft rash, umbilical plaques, nail changes (pitting, onycholysis, ridging)

— Family history: psoriasis, PsA, IBD, uveitis, AS in first-degree relatives (strong genetic component, HLA-B27, HLA-Cw6)

— Extra-articular ROS: anterior uveitis (red painful eye, photophobia), IBD symptoms, fatigue

— Triggers/risks: obesity, smoking, trauma (Koebner-like joint phenomenon), recent strep, HIV (severe PsA flare)

— PEST (Psoriasis Epidemiology Screening Tool): 5 items, score ≥3 → refer

— PsA Screen, ToPAS, EARP: alternatives

Step 3 management: In a psoriasis follow-up visit, administer PEST annually; a score ≥3 plus any swollen joint or dactylitis warrants rheumatology referral within 4–6 weeks, not a "watch and wait" approach.

PsA classically presents in five overlapping clinical patterns (Moll & Wright):

Key history elements to elicit:

Functional impact questions (key for Step 3): ability to work, button shirts, climb stairs, grip — these drive treatment escalation decisions.

Screening questionnaires in primary care:

Physical Exam Findings

— Uniform swelling of an entire digit ("sausage digit"), often with violaceous hue

— Palpate flexor tendon sheath — tenderness reflects tenosynovitis

— Leeds Dactylitis Index can quantify

— Achilles tendon insertion and plantar fascia at calcaneus

— Lateral epicondyle, medial femoral condyle, tibial tuberosity

— Iliac crest, greater trochanter

— FABER (Patrick) test, Gaenslen, direct SI palpation

— Schober test: <5 cm lumbar excursion suggests reduced spinal mobility

— Chest expansion <2.5 cm suggests costovertebral involvement

— Inspect scalp, retroauricular area, umbilicus, gluteal cleft, palms/soles, intergluteal area — common hidden sites

— Nail signs: pitting (>20 pits highly specific), onycholysis, oil-drop sign, subungual hyperkeratosis, splinter hemorrhages

Key distinction: RA produces symmetric MCP/PIP synovitis sparing DIPs, no dactylitis, no enthesitis, and no nail disease; PsA frequently involves DIPs with adjacent nail dystrophy, dactylitis, and enthesitis — a focused exam separates them before any lab returns.

General joint exam: Inspect for swelling, warmth, erythema, and effusion in peripheral joints; document tender and swollen joint counts (TJC/SJC of 66/68) — used for activity scoring (DAPSA, MDA criteria).

DIP involvement is a hallmark — palpate each DIP; tenderness + adjacent nail dystrophy strongly suggests PsA (vs. RA, which spares DIPs).

Dactylitis exam:

Enthesitis exam (SPARCC or LEI indices): Palpate

Axial/SI joint assessment:

Skin and nail exam (do not skip):

Eye exam: Conjunctival injection, ciliary flush → suspect anterior uveitis, urgent ophthalmology referral.

Cardiovascular baseline: BP, BMI, waist circumference — PsA carries increased cardiometabolic risk.

Diagnostic Workup — Initial Labs and Imaging

— CBC, CMP (baseline before DMARDs/biologics; assess renal/hepatic function)

— ESR and CRP — elevated in ~40–60% of active PsA; normal values do not exclude diagnosis (a common pitfall)

— Rheumatoid factor (RF) and anti-CCP — typically negative; positivity does not exclude PsA but lowers CASPAR points

— HLA-B27 — supports axial PsA; not diagnostic

— Uric acid — to evaluate gout in podagra-like presentations

— Hepatitis B, hepatitis C, HIV, TB (IGRA or PPD) — required before initiating biologics or methotrexate

— Lipid panel, HbA1c — cardiometabolic screening (PsA confers elevated CV risk)

— Plain radiographs of symptomatic joints, hands, feet, pelvis (SI joints), and lumbar spine

— Early disease: often normal or soft tissue swelling

— Established: erosions with adjacent new bone formation, "fluffy" periostitis, pencil-in-cup deformity, ankylosis, asymmetric sacroiliitis, syndesmophytes that are chunky and asymmetric (vs. thin marginal in AS)

Board pearl: A normal CRP/ESR does not rule out PsA — up to half of patients have normal acute-phase reactants despite active synovitis. Diagnose using clinical features + imaging, not labs alone.

PsA is a clinical diagnosis supported by labs and imaging — no single confirmatory test exists. CASPAR criteria are used (need inflammatory articular disease + ≥3 points from features below).

Initial laboratory panel:

Synovial fluid (if monoarthritis): inflammatory (WBC 2,000–50,000, neutrophil predominance), no crystals, sterile cultures — rule out septic arthritis and crystal disease.

Initial imaging:

Ultrasound of symptomatic joints/entheses: detects synovitis, tenosynovitis, enthesitis with power Doppler signal, and erosions earlier than X-ray — increasingly used in primary rheumatology workup.

Diagnostic Workup — Advanced and Confirmatory Studies

— Current psoriasis (2 points), personal/family history of psoriasis (1)

— Typical psoriatic nail dystrophy (1)

— Negative RF (1)

— Current or history of dactylitis (1)

— Radiographic juxta-articular new bone formation on hand/foot films (1)

— Sensitivity ~91%, specificity ~99%

— Hand/foot MRI: bone marrow edema, synovitis, tenosynovitis, erosions before plain film changes

— Sacroiliac joint MRI (STIR/T2 fat-suppressed): bone marrow edema → diagnoses early axial PsA when radiographs are normal

— Particularly useful in young patients with inflammatory back pain and negative X-rays

— Quantifies synovitis, identifies subclinical enthesitis

— Distinguishes dactylitis (flexor tenosynovitis + soft tissue edema) from cellulitis

Step 3 management: A 35-year-old with psoriasis, 4 months of inflammatory low back pain, normal lumbar X-ray, and HLA-B27 positive → order MRI of SI joints with STIR sequences to detect active sacroiliitis; do not stop the workup at a normal radiograph.

CASPAR Criteria (Classification Criteria for Psoriatic Arthritis) — inflammatory articular disease (joint, spine, or entheseal) PLUS ≥3 points:

MRI (most sensitive for early disease):

Musculoskeletal ultrasound with power Doppler:

Skin biopsy rarely needed — reserve for atypical rashes when psoriasis diagnosis is uncertain.

Ophthalmology evaluation with slit lamp if uveitis suspected.

Cardiometabolic workup at baseline and annually: lipid panel, HbA1c, BMI, BP — PsA increases ASCVD risk ~1.5–2×; ACC/AHA recommends considering inflammatory arthritis as a risk enhancer.

DEXA considered with chronic glucocorticoid exposure or postmenopausal status.

Risk Stratification and First-Line Management Logic

— TJC ≤1, SJC ≤1, PASI ≤1 or BSA ≤3%, patient pain VAS ≤15, patient global VAS ≤20, HAQ ≤0.5, tender entheseal points ≤1

— Peripheral arthritis

— Axial disease

— Enthesitis

— Dactylitis

— Skin and nail psoriasis

— Associated conditions (uveitis, IBD)

— Poor prognostic features: ≥5 active joints, elevated CRP, radiographic damage at baseline, dactylitis, nail involvement, prior glucocorticoid need, functional limitation

— Comorbidities that alter drug choice: latent TB, hepatitis B/C, HF, demyelinating disease, recurrent infections, malignancy history

— Mild/oligoarticular without poor prognostic markers: NSAIDs + intra-articular steroid injections for monoarthritis; reassess in 4–6 weeks

— Persistent or polyarticular: start csDMARD (methotrexate preferred)

— Inadequate response or poor prognostic features: advance to biologic DMARD (TNFi first-line) or targeted synthetic DMARD

Board pearl: Methotrexate does NOT treat axial PsA or enthesitis effectively — if these are the dominant domain, skip MTX and initiate a TNF inhibitor or IL-17 inhibitor as first-line systemic therapy.

PsA management is driven by a treat-to-target strategy aiming for minimal disease activity (MDA) or remission, reassessed every 3 months until target achieved, then every 6 months.

MDA criteria (5 of 7 needed):

Domain-based assessment (GRAPPA/EULAR) — treat each affected domain:

Risk stratification factors guiding aggressiveness:

General treatment ladder (peripheral arthritis):

Axial disease, enthesitis, dactylitis: csDMARDs (MTX) poorly effective — go directly to biologics (TNFi, IL-17i).

Non-pharmacologic foundation: weight loss (obesity reduces drug response), smoking cessation, physical therapy, low-impact exercise.

Pharmacotherapy — First-Line Drug Regimens

— Methotrexate 15–25 mg PO/SC weekly + folic acid 1 mg daily

· Best for peripheral arthritis and skin

· Limited efficacy for axial/enthesitis

· Monitor CBC, LFTs, creatinine every 4–8 weeks initially, then every 12 weeks

· Avoid in pregnancy, ETOH abuse, hepatic disease

— Sulfasalazine, leflunomide, cyclosporine — alternatives; less commonly used

— TNF inhibitors (adalimumab, etanercept, infliximab, golimumab, certolizumab): first-line biologic, effective across all domains including axial; certolizumab preferred in pregnancy (minimal placental transfer)

— IL-17 inhibitors (secukinumab, ixekizumab, bimekizumab): excellent for skin and axial; avoid in IBD (can worsen Crohn's)

— IL-23 inhibitors (guselkumab, risankizumab): strong skin efficacy; emerging joint data; not effective for axial as monotherapy

— IL-12/23 (ustekinumab): moderate joint efficacy, strong skin

— T-cell costimulation (abatacept): modest joint response

— JAK inhibitors (tofacitinib, upadacitinib): oral, effective; black box warnings — MACE, VTE, malignancy, serious infection; reserve for patients failing TNFi, especially age >65 or CV risk factors

— PDE4 inhibitor (apremilast): oral, modest efficacy, no required lab monitoring — useful in mild disease or when biologics contraindicated

Step 3 management: Before starting any biologic or JAKi, screen for latent TB (IGRA), HBV (HBsAg, anti-HBc), HCV, and HIV; update vaccines (avoid live vaccines after initiation).

NSAIDs (naproxen, ibuprofen, celecoxib): first step for mild peripheral or axial symptoms; bridge therapy during DMARD initiation. Cautions: GI bleed, renal impairment, HF, hypertension.

Intra-articular glucocorticoids: for mono/oligoarthritis or focal enthesitis; systemic steroids generally avoided — tapering can precipitate severe pustular psoriasis flare (rebound).

Conventional synthetic DMARDs (csDMARDs):

Biologic DMARDs:

Targeted synthetic DMARDs:

Expanded Pharmacology — Switching, Combinations, and Practical Use

— Switching to a second TNFi (especially if primary loss of response)

— Class switch to IL-17i, IL-23i, or JAKi (better if primary nonresponse)

— Predominant axial disease: TNFi or IL-17i (NOT MTX, NOT IL-23i monotherapy)

— Severe skin + joints: IL-17i or IL-23i

— Concurrent IBD: TNFi (infliximab, adalimumab) — avoid IL-17 inhibitors and etanercept (ineffective/worsens IBD)

— Concurrent uveitis: monoclonal TNFi (adalimumab, infliximab) — avoid etanercept

— Pregnancy planning: certolizumab pegol

— Before biologics: inactivated influenza, pneumococcal (PCV20 or PCV15→PPSV23), hepatitis B, Tdap, recombinant zoster (Shingrix), HPV

— Avoid live vaccines (MMR, varicella, yellow fever, live attenuated influenza, oral typhoid) once immunosuppressed

— CBC, CMP every 3 months

— Annual TB screening if ongoing risk

— Skin exam annually (increased non-melanoma skin cancer risk)

— Lipids 4–8 weeks after JAKi or IL-6 pathway start

Board pearl: In PsA + Crohn's disease, avoid secukinumab/ixekizumab — IL-17 blockade can worsen IBD. Choose infliximab or adalimumab, which treat both diseases.

Sequencing failure: If a TNFi fails after 3 months at full dose, options include:

Combination therapy: MTX + TNFi may reduce immunogenicity of monoclonal antibodies (infliximab, adalimumab) and prolong drug survival; etanercept and IL-17/IL-23 inhibitors do not require concomitant MTX.

Domain-tailored choices:

Vaccination strategy (critical Step 3 point):

Monitoring on therapy:

Drug holidays/perioperative: Hold biologics for one dosing interval before major surgery; resume when wound healed (~14 days).

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher baseline CV, infection, malignancy, and fall risk

— JAK inhibitors carry a black-box warning for patients ≥50 with ≥1 CV risk factor (MACE, VTE, malignancy, mortality vs. TNFi from ORAL Surveillance) — avoid as first-line in this group

— NSAIDs: increased GI bleed, AKI, HF exacerbation, hypertension — use lowest dose and shortest duration; add PPI if needed

— Glucocorticoids: heightened risk of osteoporosis, hyperglycemia, delirium, infection — minimize

— Methotrexate: reduce dose, monitor renal clearance closely

— Methotrexate contraindicated if CrCl <30 mL/min; reduce dose if CrCl 30–60 (risk of cytopenias, mucositis)

— NSAIDs avoided if CrCl <30; cautious if 30–60

— TNF inhibitors and IL-17/IL-23 inhibitors: no renal dose adjustment; generally preferred in CKD

— Apremilast: reduce dose to 30 mg daily if CrCl <30

— JAK inhibitors: dose-adjust per agent (tofacitinib reduce to 5 mg daily if moderate–severe renal impairment)

— MTX contraindicated in significant liver disease, active hepatitis, ETOH use disorder; obtain FibroScan or hepatology consult in suspected steatohepatitis (common with PsA + metabolic syndrome)

— Leflunomide also hepatotoxic

— Screen and treat HBV before biologics; chronic HBV requires antiviral prophylaxis (entecavir/tenofovir) during therapy

— HCV: prefer non-MTX agents; coordinate with hepatology for DAA treatment

Step 3 management: A 72-year-old with PsA, CKD stage 3b, and prior MI → avoid JAK inhibitors and NSAIDs; start a TNF inhibitor (after TB/hepatitis screen) and refer to cardiology for ASCVD risk optimization.

Elderly (≥65 years):

Renal impairment:

Hepatic impairment:

Frailty consideration: Use functional measures (gait speed, grip), not age alone, to guide intensity.

Special Populations — Pregnancy, Pediatrics, and Subgroups

— Disease often improves during pregnancy, flares postpartum

— Safe in pregnancy:

· Certolizumab pegol — preferred TNFi (Fc-free, minimal placental transfer); can continue through delivery

· Other TNFi (adalimumab, infliximab, etanercept) typically continued through second trimester, often stopped near term to minimize neonatal immunosuppression

· Sulfasalazine (with folate supplementation)

· Hydroxychloroquine

· Low-dose prednisone if needed

· NSAIDs only in 1st–2nd trimester; stop by 20 weeks (oligohydramnios, premature ductal closure)

— Contraindicated/teratogenic:

· Methotrexate — stop ≥3 months before conception in both partners

· Leflunomide — requires cholestyramine washout

· JAK inhibitors — avoid

— Live vaccines in infants exposed to biologics in utero: delay rotavirus and BCG until 6–12 months

Key distinction: Methotrexate is teratogenic and abortifacient — discontinue ≥3 months before conception in both men and women; certolizumab pegol is the TNFi of choice through pregnancy and lactation.

Pregnancy and lactation:

Lactation: TNFi and IL-17 inhibitors are large molecules with negligible breast milk transfer — generally compatible.

Pediatric (juvenile PsA): Subset of juvenile idiopathic arthritis; presents with dactylitis, nail pits, family history; refer to pediatric rheumatology; etanercept and adalimumab approved.

HIV-associated PsA: Often severe, explosive course; TNFi can be used cautiously if HIV well-controlled (CD4 >200, undetectable viral load); coordinate with ID.

Obesity: Independently lowers response to biologics — weight loss improves remission rates; counsel on lifestyle and consider GLP-1 RAs when indicated.

Complications and Adverse Outcomes

— Erosive joint damage with "pencil-in-cup" deformity at DIPs/PIPs

— Arthritis mutilans: telescoping fingers, severe disability (<5%)

— Ankylosis of axial spine, reduced spinal mobility, kyphosis

— Secondary osteoarthritis in damaged joints

— Uveitis (~7–25%) — typically anterior, acute, unilateral, can be bilateral/chronic; urgent slit-lamp evaluation

— Inflammatory bowel disease (~3–5%) — Crohn's > UC

— Cardiovascular disease: ~1.5–2× increased MI, stroke, atherosclerosis from systemic inflammation

— Metabolic syndrome: obesity, T2DM, hypertension, dyslipidemia, NAFLD/MASLD

— Osteoporosis — chronic inflammation + steroid use

— Depression and anxiety — both disease- and stigma-driven; impacts adherence

— Fatigue — independent symptom even with controlled inflammation

— Infections: serious bacterial, opportunistic (TB, herpes zoster, fungal), reactivation of HBV

— Malignancy: non-melanoma skin cancer (especially with cyclosporine, PUVA history); lymphoma risk modest

— Hepatotoxicity (MTX, leflunomide)

— Cytopenias (MTX)

— Demyelination (TNFi) — avoid in MS

— Heart failure exacerbation (TNFi in NYHA III–IV)

— MACE, VTE, malignancy (JAK inhibitors)

— Injection-site or infusion reactions

Board pearl: PsA confers a ~50% increased cardiovascular risk, comparable to T2DM — incorporate aggressive lipid management, BP control, smoking cessation, and weight management into every visit; treat the inflammation to reduce CV risk.

Joint complications:

Extra-articular complications:

Treatment-related complications:

Functional and economic burden: Work disability common; early DMARD initiation reduces disability progression.

When to Escalate Care — Consults and Inpatient Triage

— Acute monoarthritis with fever, severe pain — rule out septic arthritis (arthrocentesis required)

— Acute red painful eye with photophobia/visual change — emergent ophthalmology for uveitis

— New neurologic deficit with axial PsA — concern for spinal fracture, cauda equina, or cord compression

— Suspected serious infection on biologic/JAKi (fever, hypotension, focal infection): hold immunosuppression, obtain cultures, broad-spectrum antibiotics

— Severe pustular or erythrodermic psoriasis — dermatology/inpatient admission; fluid/electrolyte risk

— Any newly suspected PsA requiring DMARD initiation

— Inadequate response after 3 months of csDMARD or biologic

— Concurrent IBD or uveitis (multidisciplinary)

— Extensive skin disease (BSA >10%, PASI >10), nail disease, palmoplantar or scalp involvement requiring phototherapy or systemic skin-directed therapy

— Septic joint, necrotizing infection on biologics, severe drug reactions (DRESS from sulfasalazine), MTX pancytopenia

— Severe erythrodermic flare with hemodynamic compromise

CCS pearl: In a CCS case of suspected septic arthritis in a PsA patient on a TNF inhibitor, order arthrocentesis with cell count/differential/Gram stain/culture/crystals before antibiotics if feasible, hold the biologic, and start empiric IV vancomycin + ceftriaxone; consult orthopedics and rheumatology.

Urgent (same-day) referral or ED evaluation:

Rheumatology consultation (outpatient, within weeks):

Dermatology co-management:

Ophthalmology: any uveitis history; annual screening if HLA-B27 positive

Gastroenterology: GI symptoms suggesting IBD; chronic NSAID complications

Cardiology: elevated ASCVD risk score, established CVD, before JAKi initiation in higher-risk patients

Orthopedic surgery: advanced joint destruction, severe dactylitis not responding to therapy, joint replacement candidacy

Inpatient triage considerations:

Key Differentials — Other Inflammatory Arthritides

— Symmetric small-joint polyarthritis at MCPs, PIPs, wrists; spares DIPs

— RF and/or anti-CCP positive in ~70–80%

— No dactylitis, no enthesitis, no nail pitting, no skin psoriasis

— Radiograph: marginal erosions without new bone formation, periarticular osteopenia

— Younger males, inflammatory back pain, symmetric sacroiliitis, bamboo spine with thin marginal syndesmophytes

— Strong HLA-B27 association (~90%)

— Peripheral arthritis less common; no nail or DIP involvement

— PsA axial disease tends to be asymmetric with chunky, non-marginal syndesmophytes and frequent cervical involvement

— Post-infectious (GU: Chlamydia; GI: Salmonella, Shigella, Campylobacter, Yersinia)

— Triad: arthritis, urethritis/cervicitis, conjunctivitis

— Keratoderma blennorrhagicum, circinate balanitis — can mimic psoriasis

— Self-limited (~6 months); HLA-B27 associated

— Peripheral (Type 1 oligoarticular, parallels gut activity; Type 2 polyarticular, independent) or axial

— GI symptoms guide diagnosis

Key distinction: DIP involvement, dactylitis, enthesitis, and adjacent nail dystrophy point to PsA; symmetric MCP/PIP/wrist disease with RF/anti-CCP positivity points to RA — the presence of DIP synovitis plus nail pitting on the same finger is one of the most specific PsA findings on the boards.

Rheumatoid arthritis (RA):

Ankylosing spondylitis (AS) / axial SpA:

Reactive arthritis (Reiter):

Enteropathic arthritis (IBD-related):

Juvenile idiopathic arthritis (psoriatic subtype) in pediatric patients

SAPHO syndrome: synovitis, acne, pustulosis, hyperostosis, osteitis — overlaps with PsA spectrum

Adult-onset Still's, undifferentiated SpA

Key Differentials — Other-Category Causes

— Gout: acute monoarthritis (classic podagra at 1st MTP), tophi may mimic dactylitis; synovial fluid: negatively birefringent needle-shaped urate crystals

— CPPD/pseudogout: older patients, knee/wrist; positively birefringent rhomboid crystals, chondrocalcinosis on X-ray

— DIP/PIP nodes (Heberden/Bouchard); morning stiffness <30 min; gel phenomenon

— Imaging: osteophytes, joint space narrowing, subchondral sclerosis, "gull-wing" erosions in erosive OA

— No dactylitis, no enthesitis, no skin/nail psoriasis

Board pearl: A swollen great toe is not always gout — check for nail pits, scalp/gluteal psoriasis, and inflammatory rhythm; PsA dactylitis of the hallux can be misdiagnosed and treated with allopurinol for years. Aspirate to confirm crystals when feasible.

Crystal arthropathies:

Septic arthritis: Acute hot swollen joint with fever; can occur in PsA on immunosuppression — always aspirate a new monoarthritis

Osteoarthritis (especially erosive/inflammatory OA):

Viral arthritides: Parvovirus B19, HCV, HBV, HIV, chikungunya, alphaviruses — typically self-limited; serology guides diagnosis

Lyme arthritis: monoarticular knee, exposure history, serology, synovial fluid PCR

Fibromyalgia: widespread pain, fatigue, tender points; no synovitis, normal labs and imaging — common comorbidity in PsA that can confound activity scoring

Hypothyroid arthropathy: stiffness, effusions; check TSH

Sarcoid arthropathy / Löfgren syndrome: bilateral hilar adenopathy, erythema nodosum, ankle arthritis

Hemochromatosis: 2nd/3rd MCP "hook" osteophytes, ferritin/transferrin saturation elevated

Hypertrophic osteoarthropathy: clubbing, periostitis with lung malignancy

Cellulitis mimicking dactylitis: ill-defined erythema, fever, lymphangitic streaking — antibiotics, not DMARDs

Secondary Prevention and Long-Term Plan

— Reassess disease activity every 3 months until target (MDA/remission), then every 6 months

— Adjust therapy at each visit if target not met

— Consider tapering biologics (extending interval) only in sustained remission ≥6–12 months, never abrupt discontinuation

— Annual lipid panel, BP, HbA1c, BMI/waist circumference

— EULAR recommends multiplying calculated ASCVD risk by 1.5 in inflammatory arthritis with at-risk features

— Statin therapy per ACC/AHA guidelines; treat hypertension to <130/80 in most patients

— Smoking cessation counseling at every visit (smoking worsens PsA and reduces TNFi response)

— Mediterranean-style diet, weight loss to BMI <25 improves drug response and remission rates

— Aerobic + resistance exercise 150 min/week

— DEXA in patients on chronic glucocorticoids (≥5 mg prednisone ≥3 months) or postmenopausal

— Vitamin D 800–1000 IU + calcium 1000–1200 mg daily

— Influenza (inactivated), pneumococcal (PCV20 or PCV15→PPSV23), Tdap every 10 yr, Shingrix at age ≥19 if immunosuppressed (or ≥50), COVID-19, HBV, HPV

Step 3 management: At every routine PsA follow-up, address the "five Cs": Cardiovascular risk, Cancer screening, Calcium/bone, Cigarettes, and Comorbid mood — these prevent the long-term morbidity that often eclipses joint damage itself.

Treat-to-target maintenance:

Cardiovascular risk reduction (priority in every PsA patient):

Bone health:

Vaccinations annually:

Cancer screening: age-appropriate (mammography, colonoscopy, cervical, lung if eligible); annual skin exam for biologic users

Mental health: screen annually with PHQ-9, GAD-7

Dental care: address periodontal disease (linked to disease activity)

Eye: ophthalmology if uveitis history; annual exam if HLA-B27+

Follow-Up, Monitoring, and Counseling

— Active disease/treatment initiation: every 4–8 weeks until controlled

— Stable on therapy: every 3–6 months to rheumatology; primary care every 6–12 months

— TJC/SJC (66/68), patient global VAS, physician global VAS

— Dactylitis count, enthesitis count (LEI or SPARCC)

— Skin (BSA, PASI), nail score

— Axial symptoms (BASDAI)

— Function: HAQ-DI

— Composite measures: DAPSA, MDA, PASDAS

— MTX/leflunomide: CBC, CMP every 2–4 weeks initially, then every 8–12 weeks

— TNFi/IL-17/IL-23: CBC, CMP, every 3–6 months; annual TB screen

— JAK inhibitors: CBC, CMP, lipids 4–8 weeks after initiation, then every 3 months; herpes zoster surveillance

— Annual hepatitis serology if risk; HIV if indicated

— Adherence (biologic gaps cause anti-drug antibody formation and loss of response)

— Injection technique, self-injection support

— Signs of infection — when to hold biologic and call (fever ≥38°C, new productive cough, dysuria, cellulitis)

— Avoid live vaccines while on biologics

— Sun protection (increased non-melanoma skin cancer risk)

— Alcohol limits with MTX (≤4 drinks/week is a common practical guidance; avoid binge use)

— Contraception counseling on teratogenic agents

CCS pearl: When advancing the clock on a PsA case, after initiating MTX, schedule "return visit in 6 weeks" with CBC, CMP, and clinical reassessment; do not jump to 3 months without interim labs.

Visit cadence:

At each visit assess:

Laboratory monitoring on DMARDs/biologics:

Imaging follow-up: Radiographs of hands/feet every 1–2 years to assess radiographic progression; MRI for axial disease as clinically indicated

Patient counseling pearls:

Rehab: Physical and occupational therapy for joint protection, hand therapy for DIP disease, aquatic therapy for axial disease.

Ethical, Legal, and Patient Safety Considerations

— Discuss infection risk (including opportunistic and TB reactivation), malignancy risk, MACE/VTE risk (JAKi), demyelination, infusion reactions, cost

— Document baseline TB/HBV/HCV/HIV screening and shared decision-making

— JAK inhibitor: explicit discussion of black-box warnings in older patients or those with CV risk

— Document contraception use in patients on MTX or leflunomide

— Discuss 3-month preconception washout for MTX in both men and women; cholestyramine washout for leflunomide

— Pregnancy planning is a shared decision — coordinate with maternal-fetal medicine when appropriate

— Patients on biologics transitioning between insurers or pharmacies may face gaps in therapy → loss of response, immunogenicity

— Hospital discharge after surgery: clear plan for when to restart biologic (typically after wound healed, ~14 days, no infection)

— Communicate immunosuppression status to all providers (e.g., dental procedures, endoscopy, vaccinations)

— Document live vaccine avoidance in chart; counsel household contacts

— Infant exposed to TNFi in utero: alert pediatrician — delay live rotavirus and BCG

Board pearl: Before initiating any biologic, document four items: TB screen, HBV/HCV/HIV screen, vaccination status update, and informed consent including infection/malignancy risks — omission is a frequent malpractice and Step 3 stem trap.

Informed consent for biologics/JAK inhibitors:

Reproductive counseling:

Transition-of-care risks (highly testable on Step 3):

Vaccination safety:

Health equity: Biologic access barriers (cost, prior authorization) disproportionately affect uninsured/under-insured patients; document advocacy, manufacturer patient-assistance programs, biosimilar options

Mandatory reporting / safety: Severe adverse drug reactions (Stevens-Johnson, DRESS, anaphylaxis) — report to FDA MedWatch

Mental health and suicide risk: PsA-associated depression — document PHQ-9 screening, safety planning when positive

Driver/occupational safety on opioids or sedating agents — avoid prescribing chronic opioids for PsA pain; treat the inflammation instead

High-Yield Associations and Rapid-Fire Facts

— Dactylitis

— DIP involvement

— Dystrophic nails (pitting, onycholysis, oil drop)

— Destructive arthropathy (pencil-in-cup)

— Diffuse enthesitis

— Skin → MTX, IL-17i, IL-23i

— Peripheral arthritis → MTX, TNFi

— Axial → TNFi or IL-17i (NOT MTX)

— Enthesitis/dactylitis → TNFi, IL-17i, JAKi

— IBD overlap → TNFi (infliximab/adalimumab); avoid IL-17i

— Pregnancy → certolizumab pegol

Board pearl: A young adult with psoriasis + sausage digit + heel pain + nail pitting = PsA until proven otherwise — start workup with hand/foot/SI joint imaging, CRP, hepatitis screen, TB screen, and refer to rheumatology.

Genetics: HLA-Cw6 (skin > joint), HLA-B27 (axial PsA, uveitis), HLA-B38/B39 (peripheral PsA)

Prevalence: ~0.3–1% general population; ~20–30% of psoriasis patients

Sex: Equal overall; axial → men, peripheral polyarthritis → women

Five Moll & Wright patterns: asymmetric oligoarthritis, symmetric polyarthritis, DIP-predominant, axial, arthritis mutilans

Hallmark features (5 D's of PsA mnemonic):

Radiographic signs: pencil-in-cup, marginal erosions WITH adjacent new bone formation ("fluffy" periostitis), asymmetric sacroiliitis, chunky non-marginal syndesmophytes, ankylosis, "ivory phalanx"

CASPAR criteria for classification (≥3 points + inflammatory MSK disease)

Screening tool: PEST (score ≥3 refer)

Score for activity: DAPSA; target: MDA or remission

Treatment by domain:

Comorbidities: CV disease, metabolic syndrome, NAFLD, uveitis, IBD, osteoporosis, depression

HIV + PsA: explosive course; TNFi cautiously if controlled

Koebner phenomenon: trauma triggers new plaques — also seen in lichen planus, vitiligo

Auspitz sign: pinpoint bleeding on plaque scraping

Steroid withdrawal: can cause pustular psoriasis flare — avoid systemic steroid bursts

Board Question Stem Patterns

— PsA + Crohn's: choose infliximab or adalimumab (avoid IL-17i, etanercept)

— PsA + pregnancy: certolizumab pegol

— PsA + multiple sclerosis: avoid TNFi → choose IL-17i or IL-23i

— PsA + recurrent infections/CHF: avoid TNFi → IL-17i/IL-23i or apremilast

— PsA + age >65 with CV risk: avoid JAK inhibitors

Step 3 management: When two biologics seem equally appropriate, the comorbidity sidebar (IBD, uveitis, pregnancy, MS, infection, CV risk) is the deciding factor — Step 3 questions almost always hide the answer in the patient's other diagnoses.

Stem 1 — Classic recognition: 40-year-old with 10-year history of scalp/elbow plaques presents with 6 months of right 3rd toe "sausage-like" swelling, morning stiffness, heel pain. Exam: pitted nails. Answer: Diagnose PsA clinically, screen with CRP/RF/CCP, image, refer rheumatology.

Stem 2 — Hidden psoriasis: 35-year-old with asymmetric oligoarthritis and RF/anti-CCP negative; on exam, scalp and gluteal cleft plaques noted. Answer: Psoriatic arthritis (sine psoriasis until you check hidden sites).

Stem 3 — Axial disease workup: Young patient with inflammatory back pain, psoriasis, normal X-ray. Answer: MRI of SI joints with STIR.

Stem 4 — Treatment selection by comorbidity:

Stem 5 — Pre-biologic checklist: What test before starting adalimumab? Latent TB screen (IGRA), HBV, HCV, HIV, vaccination update.

Stem 6 — Steroid pitfall: Patient with PsA flare given oral prednisone burst, tapered, then develops generalized pustular eruption. Answer: Pustular psoriasis precipitated by steroid taper; avoid systemic steroids in psoriasis.

Stem 7 — Differential trap: Symmetric small-joint arthritis with RF positive → RA, not PsA, even if patient has psoriasis (mixed; treat as RA pattern but biologics work for both).

Stem 8 — Dactylitis mimic: Diabetic with red painful swollen finger and fever → cellulitis/flexor tenosynovitis, not PsA dactylitis.

Stem 9 — Long-term care: Best next step in stable PsA patient on TNFi → annual CV risk assessment, vaccines, skin cancer screen.

Stem 10 — CCS flow: Suspected septic arthritis on biologic → aspirate, cultures, hold biologic, empiric vancomycin + ceftriaxone, ortho consult.

One-Line Recap

Psoriatic arthritis is a seronegative inflammatory arthritis suspected in any psoriasis patient with morning stiffness, dactylitis, enthesitis, DIP synovitis, or nail dystrophy — diagnosed clinically by CASPAR criteria, screened annually with PEST, and treated to target with domain-tailored therapy that also reduces the elevated cardiovascular and metabolic risk that accompanies the disease.

Board pearl: The Step 3 PsA question is rarely "what is the diagnosis?" — it is "what is the next best step, given this comorbidity?" Master the comorbidity-to-biologic matching and the pre-biologic safety checklist and the topic is solved.

Recognize: Inflammatory rhythm + skin/nail psoriasis + dactylitis/enthesitis/DIP disease; check hidden sites (scalp, umbilicus, gluteal cleft, nails); normal CRP does not rule it out.

Screen and refer: Use PEST annually in every psoriasis patient; score ≥3 with any joint complaint → rheumatology within weeks. Pre-biologic checklist: TB, HBV, HCV, HIV, vaccinations.

Treat by domain: MTX for peripheral arthritis/skin; TNFi or IL-17i for axial disease, enthesitis, dactylitis (MTX is ineffective for these); choose biologic by comorbidity — IBD → TNFi (avoid IL-17i); pregnancy → certolizumab; uveitis → monoclonal TNFi; age >65 with CV risk → avoid JAKi.

Prevent long-term harm: Aggressive cardiovascular risk reduction, bone health, mental health screening, cancer surveillance, and avoidance of systemic steroid bursts (rebound pustular psoriasis) — the inflammation, not just the joints, is what shortens life.