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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- PsA is inflammatory arthritis associated with psoriasis and nail disease
- Key clues: dactylitis, enthesitis, DIP arthritis, axial disease, asymmetric oligoarthritis
- RF/anti-CCP are usually negative
- Radiographs show erosions with new bone formation
- Treatment depends on dominant domain and may require biologics
Overview
Psoriatic arthritis is a seronegative spondyloarthritis associated with psoriasis, nail disease, dactylitis, enthesitis, peripheral arthritis, and axial disease. Arthritis can precede psoriasis.
Epidemiology
Occurs in a substantial minority of psoriasis patients. Severe psoriasis, nail disease, scalp/intergluteal disease, obesity, and family history increase risk.
Clinical Features
Symptoms
Asymmetric joint pain and morning stiffness
DIP pain with nail pitting or onycholysis
Dactylitis or sausage digit
Heel pain from enthesitis
Inflammatory back pain
Painful red eye suggesting uveitis
Signs
Psoriatic plaques in scalp, extensor, umbilical, or gluteal cleft sites
Nail pitting, ridging, hyperkeratosis, or onycholysis
Dactylitis, enthesitis, or asymmetric synovitis
Achilles or plantar fascia tenderness
Arthritis mutilans in severe disease
Investigations
First-line
Focused clinical assessmentPattern recognition, red flags, functional impact, and targeted examination
Basic labs when indicatedCBC, CMP, ESR/CRP, CK, urinalysis, or disease-specific testing depending on suspected condition
Initial imaging when indicatedPlain radiographs or MRI/ultrasound based on suspected structural, inflammatory, infectious, or neurologic disease
Second-line
Disease-specific confirmatory testingAutoantibodies, HLA-B27, synovial fluid, nerve conduction studies, DEXA, or cultures as appropriate
MRI/ultrasound/CTUsed for early inflammatory disease, occult fracture, tendon tear, infection, or surgical planning
Screening before immunosuppressionTB, hepatitis, vaccination review, and baseline labs when biologic or high-risk therapy is planned
Specialist
Specialist referralRheumatology, orthopedics, infectious disease, ophthalmology, neurology, or spine surgery depending on red flags and disease severity
1
Initial management
- Address red flags and emergencies first
- Use guideline-directed first-line therapy matched to disease severity
- Educate the patient and set functional goals
- Use analgesia and rehabilitation when appropriate
2
Escalation
- Escalate to specialist-directed therapy if severe, refractory, progressive, or organ-threatening disease
- Use imaging, procedures, immunosuppression, antibiotics, or surgery according to diagnosis
- Monitor response objectively and revise diagnosis if response is atypical
3
Prevention and follow-up
- Manage comorbidities and medication toxicity
- Vaccinate and screen when immunosuppression is used
- Prevent disability, falls, fracture, infection, and functional decline
Complications
- Functional impairment: Pain, weakness, stiffness, deformity, or disability depending on disease
- Diagnostic delay: Missed infection, fracture, inflammatory disease, neurologic compromise, or organ-threatening complication
- Medication toxicity: NSAID, steroid, antibiotic, anticoagulation, opioid, or immunosuppressive adverse effects
- Chronic disease burden: Reduced quality of life, work impairment, deconditioning, and mental health impact
USMLE Step 2 CK Exam Tips
- 1Psoriasis + nail pitting + DIP arthritis = PsA
- 2Sausage digit = dactylitis
- 3Pencil-in-cup deformity is classic
- 4RF/anti-CCP usually negative
- 5Look for hidden plaques
- 6IL-17 inhibitors can worsen IBD
practicetest your knowledge on psoriatic arthritisApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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