Psoriatic Arthritis

Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis, seronegative for rheumatoid factor.

• Develops in 20 to 30% of patients with psoriasis, typically 5 to 10 years after skin onset, though arthritis precedes skin disease in 15%.

• Risk factors: nail disease, scalp or intergluteal psoriasis, obesity, HLA-B27, HLA-C06, trauma.

• Patterns: oligoarthritis, polyarthritis, distal interphalangeal predominant, spondylitis, arthritis mutilans.

• Mediated by TNF, IL-17, IL-23. Comorbidities: metabolic syndrome, cardiovascular disease, uveitis, inflammatory bowel disease, fatty liver.

• Erosive disease occurs in up to 50% within 2 years if untreated.

• Asymmetric oligoarthritis, dactylitis ("sausage digit"), enthesitis (Achilles, plantar fascia), inflammatory back pain.

• Nail pitting, onycholysis, and distal joint disease correlate strongly.

• Morning stiffness, fatigue, pencil-in-cup deformity in arthritis mutilans.

• Differentials: rheumatoid arthritis, gout, osteoarthritis, reactive arthritis.

• CASPAR criteria: inflammatory articular disease plus 3 points from psoriasis, nail dystrophy, negative rheumatoid factor, dactylitis, juxta-articular new bone formation.

• Radiographs: erosions with adjacent bone proliferation, periostitis, pencil-in-cup, asymmetric sacroiliitis. Ultrasound or MRI for synovitis and enthesitis.

• CRP and ESR (may be normal), rheumatoid factor and anti-CCP (mostly negative), uric acid, HLA-B27 if axial.

• Assess disease activity (DAPSA, minimal disease activity), skin (PASI), cardiovascular risk, liver tests, hepatitis B/C and TB screen before therapy.

• NSAIDs for mild disease: naproxen 500 mg twice daily. Local steroid injection for oligoarthritis (triamcinolone 20 to 40 mg).

• Peripheral polyarthritis: methotrexate 15 to 25 mg weekly with folic acid 5 mg weekly, leflunomide 20 mg daily, or sulfasalazine 2 to 3 g daily.

• Biologics for inadequate response or axial, enthesitic, severe disease: TNF inhibitors (adalimumab 40 mg every 2 weeks, etanercept 50 mg weekly, golimumab, certolizumab), IL-17 inhibitors (secukinumab 300 mg then monthly, ixekizumab 80 mg every 4 weeks, bimekizumab 160 mg every 4 weeks), IL-23 inhibitors (guselkumab 100 mg every 8 weeks, risankizumab 150 mg every 12 weeks), ustekinumab 45 to 90 mg every 12 weeks.

• Oral agents: apremilast 30 mg twice daily (mild to moderate), tofacitinib 5 mg twice daily, upadacitinib 15 mg daily.

• Choose by dominant domain: IL-17/IL-23 for severe skin disease; avoid IL-17 in active inflammatory bowel disease (use adalimumab or infliximab); adalimumab for uveitis.

• Manage comorbidities: weight loss, statin, blood pressure, glucose.

• Treat to target: remission or minimal disease activity, reassess every 3 months.