Psoriatic arthritis
Recently recognized,
underdiagnosed subset of JIA; 2–15% of children with JIA; unknown aetiology on
a background of strong genetic predisposition (up to 50%).
•
Inflammatory
arthritis in presence of psoriasis, or inflammatory arthritis with dactylitis
or psoriatic nail changes plus a first-degree relative with psoriasis.
•
Exclusions: RF +ve; HLA-B27 +ve in male
>6yrs; any enthesitis-related arthritis
or uveitis in first-degree relative; systemic arthritis.
•
Arthritis
and rash rarely present simultaneously. Rash usually precedes arthritis.
•
Arthritis: commonest is asymmetrical large
joint (knees or ankles). Small joint
polyarthritis of fingers and toes (metacarpal phalangeal (MCP), proximal
interphalangeal (PIP), and distal interphalangeal (DIP) joints) and dactylitis
are also common. Some children have tendonitis or tenosynovitis, especially
around the ankles.
•
Skin: predominantly plaque psoriasis
(examine extensor surfaces of elbows
and knees, hairline, behind the ears, around the umbilicus, groin, and natal
cleft;).
•
Nails: pitting, ridging, onycholysis,
subungual hyperkeratosis.
•
Uveitis: needs regular screening as can
potentially blind.
•
Psoriasis
affects up to 3% of normal population; the association with inflammatory
arthritis may be coincidental.
•
No specific tests: need exclusion bloods.
•
Often evidence of chronic
inflammation: raised
CRP; thrombocytosis; and low grade
normocytic anaemia.
•
Periarticular
osteopenia and soft tissue swelling.
•
Periosteal
new bone formation, particularly in dactylitis.
Important to diagnosis dactylitis.
NSAIDs are the mainstay of treat-ment. Intra-articular steroid injections often
help settle inflammation. Methotrexate and ant-TNF agents are effective for
persistent disease.
Arthritis can be episodic and
continue into adult life. A few patients have a very destructive
course with arthritis mutilans.
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