This condition develops in approximately 20% of patients who have psoriasis.1 Psoriatic arthritis is classified into 4 clinical subgroups:
- Arthritis confined primarily to distal interphalangeal joints of the hands and feet.
- Asymmetric oligoarthritis with dactylitis and ankylosing spondylitis, with or without associated peripheral joint involvement.
- Symmetric arthritis mutilans.
- Polyarthritis that is similar to rheumatoid arthritis.
The characteristic lesions of psoriasis—sharply demarcated inflammatory plaques with silvery scale (A)—usually, but not always, precede arthritis. The lesions can occur anywhere but usually are found over the extensor surfaces of joints (elbows and knees), on the scalp, in the umbilicus, behind the ears, and in the presacral area. Gentle scraping usually produces pinpoint bleeding. Nonspecific signs of nail involvement include onycholysis, ridging, subungual keratosis, and discoloration. Pitting, which often produces more than 20 indentations in a single fingernail, is strongly associated with distal interphalangeal synovitis and is quite common in psoriasis (B).
1. Gladman DD. Clinical aspects of the spondyloarthropathies. Am J Med Sci. 1998;316:234-238.