Psoriatic Arthritis (PsA)
Seronegative inflammatory arthritis associated with psoriasis; classic features include dactylitis, enthesitis, and DIP involvement.
Also known as: PsA, psoriatic arthritis
Overview
Inflammatory arthritis occurring in patients with cutaneous or nail psoriasis. A heterogeneous disease that can affect peripheral joints (including DIPs), entheses, the axial skeleton, and digits (dactylitis), often in asymmetric patterns.
Epidemiology
Develops in 20-30% of patients with psoriasis. Skin disease usually precedes joint disease by years, but arthritis can appear first in 10-15%. Onset peaks 30-50; men and women affected roughly equally (axial disease more common in men).
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Risk factors
- Cutaneous psoriasis (especially severe or with nail involvement)
- Family history of psoriasis or psoriatic arthritis
- HLA-B27 (axial PsA)
- Obesity (worsens disease and reduces drug response)
- Smoking
- Trauma (Koebner phenomenon in joints — deep Koebner)
Pathophysiology
Combined synovitis and enthesitis driven by TNF-alpha, IL-17, and IL-23 pathways. Genetic susceptibility (HLA-B27, HLA-Cw6, IL-23R variants) plus environmental triggers produce inflammation at synovium, entheses, nails, and skin.
Clinical presentation
Symptoms
- Joint pain with morning stiffness >30 minutes, improving with activity
- Asymmetric oligoarthritis (most common pattern), DIP-predominant, polyarticular RA-like pattern, arthritis mutilans, or axial pattern
- Dactylitis — sausage digit from combined tenosynovitis and arthritis
- Enthesitis — Achilles, plantar fascia, lateral epicondyle
- Heel pain, low back pain (inflammatory pattern)
- Skin and nail findings — plaque psoriasis (look for hidden sites: scalp, umbilicus, gluteal cleft, behind ears) and nail pitting, onycholysis, oil drop sign
Signs / physical exam
- Asymmetric synovitis often involving DIPs
- Dactylitis — entire digit swollen, tender
- Enthesitis at Achilles insertion, plantar fascia, patellar insertion
- Nail changes: pitting, onycholysis, subungual hyperkeratosis
- Skin plaques
- Reduced spinal mobility if axial involvement
Differential diagnosis
- Rheumatoid arthritis — Symmetric MCP/PIP/wrist synovitis, positive RF/CCP, no DIP unless OA also present; no enthesitis or dactylitis
- Osteoarthritis (especially erosive hand OA) — DIP involvement with Heberden nodes, mechanical pattern, normal CRP
- Gout — Acute monoarticular flares, MSU crystals, can mimic PsA in feet
- Reactive arthritis — Post-infectious oligoarthritis, conjunctivitis, urethritis; HLA-B27
- Ankylosing spondylitis — Pure axial disease without psoriasis or skin findings
- IBD-associated arthritis — Coexisting Crohn or UC; peripheral or axial pattern
Diagnostic workup
Diagnostic criteria
CASPAR classification criteria: inflammatory articular disease (joint, spine, or entheseal) plus ≥3 points from psoriasis, nail changes, RF-negative, dactylitis history, and juxta-articular new bone formation.
Labs
- RF and anti-CCP — typically NEGATIVE (some patients have low-titer positivity)
- ESR, CRP — variably elevated; can be normal in active disease
- HLA-B27 — supportive in axial disease
- Uric acid — exclude gout in monoarticular flare
Imaging
- Plain radiographs — 'pencil-in-cup' deformity at DIPs, periostitis, fluffy new bone formation, marginal erosions, ankylosis, asymmetric sacroiliitis, non-marginal syndesmophytes (large, asymmetric, parasyndesmophytes)
- Ultrasound or MRI — detects enthesitis, synovitis, dactylitis, and bone marrow edema before radiographic change
Diagnostic algorithm
| Feature | RA | PsA |
|---|---|---|
| Symmetry | Symmetric | Often asymmetric |
| DIP involvement | Rare | Common |
| Dactylitis | No | Yes (hallmark) |
| Enthesitis | No | Yes (hallmark) |
| RF / anti-CCP | Positive 70-80% | Typically negative |
| Nail changes | No | Pitting, onycholysis |
| Radiograph | Marginal erosions, periarticular osteopenia | Pencil-in-cup, periostitis, new bone |
| Axial disease | Cervical only (C1-C2) | Sacroiliitis (often asymmetric), syndesmophytes |
Treatment
First-line
- Mild peripheral disease: NSAIDs — naproxen, ibuprofen, meloxicam — plus intra-articular steroid injections
- Conventional DMARDs for peripheral arthritis: methotrexate, sulfasalazine, leflunomide (also helps skin disease, especially MTX)
- Treat skin disease in parallel with topical agents and phototherapy as needed
Second-line / adjunct
- TNF inhibitors — etanercept, adalimumab, infliximab, golimumab, certolizumab — broadly effective for skin, joint, axial, and entheseal disease
- IL-17 inhibitors — secukinumab, ixekizumab — particularly effective for skin and enthesitis (avoid in IBD)
- IL-23 inhibitors — guselkumab, risankizumab — emerging first-line biologic for skin and joints
- IL-12/23 inhibitor — ustekinumab
- JAK inhibitors — tofacitinib, upadacitinib
- PDE4 inhibitor — apremilast — modest efficacy, well-tolerated oral option
- Avoid systemic corticosteroids when possible — withdrawal can trigger pustular psoriasis
Complications
- Joint destruction, arthritis mutilans (telescoping digits)
- Functional disability and reduced quality of life
- Comorbidities: cardiovascular disease, metabolic syndrome, obesity, fatty liver, depression, uveitis, IBD
- Increased cardiovascular mortality independent of traditional risk factors
PANCE pearls
- Look for psoriasis in hidden sites — scalp, umbilicus, gluteal cleft, behind the ears — before excluding PsA in a patient with inflammatory arthritis.
- Dactylitis and enthesitis are highly characteristic; DIP involvement with nail pitting strongly suggests PsA over RA.
- Pencil-in-cup deformity is the classic radiographic finding.
- Systemic steroid tapers can trigger pustular psoriasis flares — avoid when possible.
- Treat-to-target with regular assessment of joint, skin, and patient-reported outcomes is now standard.
References
- ACR/NPF 2018 — 2018 ACR/NPF Guideline for the Treatment of Psoriatic Arthritis (Singh et al., Arthritis Rheumatol 2019)
- GRAPPA 2021 — GRAPPA Treatment Recommendations for Psoriatic Arthritis (Coates et al., Nat Rev Rheumatol 2022)
- CASPAR — Classification Criteria for Psoriatic Arthritis (Taylor et al., Arthritis Rheum 2006)
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