Psoriatic arthritis is a seronegative inflammatory disorder; approximately 5% of psoriatic patients develop arthritis. HLA B27 is present in 40% of psoriatics with spondylitis whereas HLA DR3 and HLA DR4 correlate with more severe and erosive peripheral disease.
Psoriasis may precede joint disease, or the onset may be synchronous, or arthritis may precede psoriasis
Psoriatic arthritis has five subgroups. These are:
|1.||Classical psoriatic arthritis, predominantly involving the distal interphalangeal joints (DIP) of the hands and feet. Nail changes like pitting, onycholysis and hyperkeratosis are often associated.|
|2.||Arthritis mutilans, with sacroiliitis characterised by osteolysis and gross deformities leading to the appearance of a severely deformed flail hand with shortening of one or two digits and consequent telescoping.|
|3.||A symmetrical polyarthritis resembling rheumatoid arthritis but with negative serology; it is often less extensive and more benign.|
|4.||Asymmetrical, pauciarticular, small or large joint involvement with ‘sausage’ digits.|
|5.||Ankylosing spondylitis with or without peripheral arthritis.|
The sacroiliitis is frequently asymmetrical and may be associated with spondylitis, sometimes clinically indistinguishable from ankylosing spondylitis.
Enthesitis, or inflammation at the tendon or ligamentous attachment to bone, is characteristically observed at the achilles tendon and around the pelvis. Plantar fasciitis is also common.
The most common ocular involvement is conjunctivitis, occurring in 20% of patients. The palmoplantar pustular psoriasis is often associated with inflammatory condition of the anterior chest wall. Explosive and severe form of psoriasis with onychodystrophy may occur in association with HIV infection; it carries a poor prognosis.
The most common clinical manifestations in children include asymmetrical polyarthritis involving the digits, pauciarticular disease mainly affecting the knees and/or spondylitis. Arthritis precedes psoriasis in a majority of these cases.
|1||Negative rheumatoid factor and ANA|
|2||Elevated serum uric acid|
|3||Radiological features, including asymmetrical syndesmophytes, osteolysis of DIP joints with cup-and-pencil deformities, periosteitis, paraspinal calcification, and proliferative new bone formation at enthesis|