About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Inflammatory arthritis in a patient with psoriasis (skin disease may precede, follow, or occur simultaneously with arthritis)
- Five patterns: asymmetric oligoarthritis (most common), DIP-predominant, symmetric polyarthritis (RA-like), spondylitis, arthritis mutilans
- Distinguishing features from RA: DIP involvement, dactylitis (sausage digits), enthesitis, nail changes, psoriatic plaques
- RF and anti-CCP typically NEGATIVE (seronegative arthropathy)
- Treatment: methotrexate first-line DMARD, anti-TNF or anti-IL-17 biologics if refractory
Overview
Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy associated with psoriasis, classified within the seronegative spondyloarthropathies. It affects approximately 20–30% of people with psoriasis. The five classical patterns described by Moll and Wright are: asymmetric oligoarthritis (~40%, most common), distal interphalangeal joint predominant (~10%), symmetric polyarthritis resembling RA (~25%), spondylitis/sacroiliitis (~5%), and arthritis mutilans (~5%, severe destructive). In practice, patterns overlap and may evolve over time. Dactylitis, enthesitis, and nail disease are hallmark features that help distinguish PsA from RA.
Epidemiology
PsA affects approximately 0.1–0.2% of the general population and ~20–30% of those with psoriasis. Skin psoriasis precedes arthritis in ~70%, occurs simultaneously in ~15%, and arthritis precedes skin disease in ~15%. Age of onset is typically 30–50 years. Equal sex distribution. HLA-B27 is associated with the spondylitis subtype. Risk factors include severe skin psoriasis, nail disease, family history, and obesity.
Clinical Features
Symptoms
Joint pain and stiffness with inflammatory pattern (morning stiffness >30 min)
DIP joint involvement (distinctive feature — DIP spared in RA)
Dactylitis: diffuse sausage-like swelling of an entire digit
Enthesitis: pain at tendon insertions (Achilles, plantar fascia, epicondyles)
Psoriatic skin lesions (check scalp, natal cleft, umbilicus, behind ears — may be subtle)
Nail changes: pitting, onycholysis, subungual hyperkeratosis, oil-drop sign — present in ~80% of PsA
Low back pain (if axial involvement/sacroiliitis)
Signs
Synovitis of DIPs, PIPs, MCPs — often asymmetric or DIP-predominant
Dactylitis: diffusely swollen tender digit
Psoriatic plaques (may be hidden in scalp, natal cleft, umbilicus)
Nail pitting (>20 pits is highly suggestive), onycholysis, oil-drop discolouration
Entheseal tenderness at bony insertions
Pencil-in-cup deformity and telescoping digits (arthritis mutilans — rare, severe)
Investigations
First-line
Inflammatory markersCRP and ESR may be raised (but can be normal)
RF and anti-CCPTypically NEGATIVE — PsA is a seronegative arthropathy. If RF positive, consider coexistent RA or that RF is coincidentally positive (~5% of PsA patients are RF positive)
X-rays of affected jointsPeriarticular erosions, pencil-in-cup deformity (arthritis mutilans), periostitis, enthesophytes. DIP erosions distinguish from RA. Joint space may be narrowed or widened (ankylosis)
Second-line
MRI or USS jointsMore sensitive for early synovitis, enthesitis, dactylitis than X-ray
MRI sacroiliac jointsIf axial symptoms — may show sacroiliitis
Specialist
DAPSA or MDA scoresDisease Activity for Psoriatic Arthritis (DAPSA) or Minimal Disease Activity (MDA) — used to guide treatment decisions
1
First-line
- NSAIDs for symptom relief (particularly for axial disease and enthesitis)
- Intra-articular corticosteroid injections for oligoarthritis
- Early referral to rheumatology — do not delay DMARD initiation
2
DMARDs (peripheral disease)
- Methotrexate: first-line DMARD for peripheral PsA (also treats skin psoriasis)
- Alternatives: leflunomide, sulfasalazine
- Conventional DMARDs do NOT work for axial disease (same as AS)
3
Biologic and targeted therapies
- Anti-TNF: adalimumab, etanercept, infliximab, certolizumab, golimumab — effective for joints, skin, enthesitis, dactylitis, and axial disease
- Anti-IL-17: secukinumab, ixekizumab — effective for peripheral and axial PsA
- Anti-IL-12/23: ustekinumab — effective for peripheral PsA and skin
- PDE4 inhibitor: apremilast — oral, for mild-moderate PsA if DMARDs and biologics not suitable
- JAK inhibitors: tofacitinib, upadacitinib
Complications
- Joint destruction: Progressive erosive arthritis, particularly arthritis mutilans subtype
- Anterior uveitis: Occurs in ~7–10% — particularly in HLA-B27-positive spondylitis subtype
- Cardiovascular disease: Increased CV risk — systemic inflammation
- Metabolic syndrome: Obesity, diabetes, dyslipidaemia — commonly associated
- Depression: Chronic pain and skin disease — screen regularly
UKMLA Exam Tips
- 1DIP joint involvement + nail changes + dactylitis = psoriatic arthritis (DIP spared in RA)
- 2RF and anti-CCP are NEGATIVE — seronegative arthropathy. If RF positive in an arthritis patient with psoriasis, still consider PsA
- 3Look for hidden psoriasis: scalp hairline, natal cleft, umbilicus, behind ears — may be subtle or absent
- 4Nail pitting is a strong predictor of PsA in psoriasis patients
- 5Pencil-in-cup deformity = arthritis mutilans (rare destructive subtype)
- 6Dactylitis and enthesitis link PsA to the spondyloarthropathy family
- 7Arthritis precedes skin disease in ~15% — PsA can occur without visible psoriasis (sine psoriasis)
practicetest your knowledge on psoriatic arthritisApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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