AKT · Musculoskeletal/Inflammatory arthritis

Psoriatic arthritis

Seronegative inflammatory arthritis associated with psoriasis

Overview

An inflammatory arthritis associated with psoriasis (which may precede, accompany or follow the joint disease). It has several patterns — including a DIP-predominant form, asymmetrical oligoarthritis, a symmetrical RA-like polyarthritis, spondylitis, and the destructive arthritis mutilans. Dactylitis, enthesitis and nail changes are clues.

Recognise

Joint pain/swelling with psoriasis (skin or nail); DIP-joint involvement, dactylitis ('sausage digit'), enthesitis
Nail changes: pitting, onycholysis; X-ray 'pencil-in-cup' deformity; arthritis mutilans (telescoping digits) in severe disease
Several patterns: DIP, asymmetrical oligoarthritis, symmetrical (RA-like), spondylitis, arthritis mutilans

Red flags

Arthritis mutilans (rapidly destructive) → urgent rheumatology and aggressive therapy
Psoriatic disease + new inflammatory back pain → axial involvement

Differentials & how to tell them apart

Rheumatoid arthritissymmetrical MCP/PIP, RF/anti-CCP positive, DIP spared, no psoriasis/dactylitis

OsteoarthritisDIP nodes (Heberden) but non-inflammatory, no dactylitis/nail pitting

Goutacute monoarthritis with crystals; tophi

Psoriatic arthritis — erosive change of the interphalangeal joints (hand X-ray)
Cecco / Public domain — Wikimedia Commons

Investigations

Clinical (psoriasis + inflammatory arthritis); usually RF/anti-CCP negative; X-rays (DIP erosions, 'pencil-in-cup', osteolysis); raised inflammatory markers; screen skin/nails; PEST screening tool in psoriasis clinics.

Management

NSAIDs/intra-articular steroid → methotrexate for peripheral disease → biologic if refractory

1Diagnose from psoriasis + inflammatory arthritis (dactylitis/enthesitis/nail change). Mild peripheral disease → NSAIDs ± intra-articular steroid; persistent → methotrexate (which also treats the skin).Gate: Axial or arthritis-mutilans disease responds poorly to conventional DMARDs → escalate to a biologic (anti-TNF/IL-17).
2Inadequate response or severe/axial disease → biologic or targeted synthetic DMARD; coordinate skin and joint care with dermatology.

NSAIDs ± intra-articular steroid for mild disease — symptomatic; for limited peripheral joint involvement

Conventional DMARD (methotrexate) for peripheral arthritis — also helps skin psoriasis; leflunomide/sulfasalazine alternatives

Biologic (anti-TNF, IL-17, IL-12/23) or targeted DMARD — for inadequate response or axial/severe disease; treats skin and joints

Treat the skin disease — joint and skin disease managed together (dermatology cross-ref)

Key points

Inflammatory arthritis + psoriasis + dactylitis/nail pitting + DIP involvement + 'pencil-in-cup' = psoriatic arthritis → methotrexate for peripheral disease (treats skin too), biologic for axial/severe. Often RF-negative.

Monitor & prognosis

Joint and skin activity, X-ray progression, biologic safety screen.

Variable; early treatment limits the destructive forms.

Source: NICE NG65 (spondyloarthritis); cross-ref dermatology (psoriasis)