Musculoskeletal · PANCE / PANRE

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

Differentiating RA from PsA — the high-yield boards comparison.

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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