Psoriatic arthritis

Inflammatory arthritis in 2-4% of those with psoriasis (psoriasis affects 1-2% of population). Most have previous long history of psoriasis – all forms of psoriasis can develop arthritis. High association with HLA-B27 and HIV infection.

5 broad clinical types (of good clinical use, but no broad agreement on classification for epidemiological purposes or clinical trials – overlap between types does occur often):
1) Oligoarticular & polyarthritis with distal interphalangeal joint involvement and other ‘scattered’ joints (often less than four) - asymmetric – usually get the classic ‘sausage’ digits (affects 50-70%).
2) Asymmetric involvement of distal interphalangeal joints of hands and feet – digits affected - usually have nail changes; progressive bone erosions frequently occur (affects 5-10%)
3) Symmetric seronegative polyarthritis resembling rheumatoid arthritis (in 15-25%; morning stiffness and fatigue are common) – usually milder/less destructive than rheumatoid arthritis and does not develop extra-articular manifestations.
4) Sacroilitis and spondylitis (in 5%; resembles ankylosing spondylitis) – spinal involvement is predominant feature
5) Arthritis mutilans (widespread destructive polyarthritis with marked bone resorption; in about 1-5%; often get osteolysis of bones in fingers and toes; frequently get back pain)
*May also hypothetically get a coincidental rheumatoid arthritis and psoriasis (due to prevalence of both diseases in community)

SAPHO Syndrome – synovitis, acne, pustulosis, hyperostosis, osteomyelitis
• sometimes classified as ‘6th’ clinical type
• more common in Europe than USA
• associated with the palmopustular psoriasis
• not clear if it is a form of psoriatic arthritis

Clinical features:
M=F, usually 35-50 years (juvenile form, usually 9-12 years). Symptoms are variable due to different clinical types. IPJ’s of fingers and toes most commonly involved – knee and ankle are occasionally involved.
Arthritis precedes or occurs simultaneously with the onset of the psoriasis in about a third of cases.
No relationship between severity of psoriasis and psoriatic arthritis, but the arthritis is more common in those with more severe skin lesions. There is a relationship between severity of psoriatic nail changes and arthritis.
Occasionally have fatigue, fever, conjunctivitis and iritis
Crystal induced arthropathy has a higher incidence in those with psoriatic arthritis.

Laboratory tests – raised ESR, mild neutropenia, raised gammaglobulins, no RA factor, mild anaemia, high neutrophil count in synovial fluid.

Differential diagnosis – Reiter syndrome, gout, rheumatoid arthritis.

Indicators of poorer prognosis:
Earlier age of onset; HLA-B27 (spondylosis); HLA-DR3, DR4 (erosive disease); significant skin involvement; polyarticular arthritis; poor response to NSAID’s; associated with HIV infection.

Involvement of foot:
Heel pain is presenting feature in up to 10%
Usually bilateral and asymmetric – foot is one of most common sites of arthritis and may be initial presenting feature of psoriatic arthritis – usually IPJ’s.
• Posterior tibial dysfunction may be presenting feature of psoriatic arthritis – other tendon sheaths can also be commonly involved
• X-ray of foot - marginal erosions (bilateral and symmetrical), bone proliferation, joint space loss (often severe), osteolysis of distal tufts, destruction of IPJ’s, ‘pencil in a cup’ deformity of phalanges. Calcaneus will generally show proliferative and erosive changes of posterior and inferior aspects. Achilles tendon may be thickened.
• “Sausage toe” – toe is swollen (dactylitis) – due to involvement of MPJ, PIPJ and DIPJ’s – shows up on bone scan as a ‘hot toe’.
• up to 70% get plantar heel pain – other entheses also get affected
• distal involvement of the plantar fascia can also occur
• Tarsal tunnel syndrome
Nail changes – (in 80%) - pitting, ridging, hyperkeratosis and onycholysis

Management:
• Managed similar to rheumatoid arthritis, but prognosis is better.
• Physical therapy & rehabilitation (preserve joint range of motion and strength muscle)
• Drugs (NSAID’s; gold salts; antimalarials, sulfasalazine; immunosuppressive drugs; corticosteroids)

 
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