[Psoriatic rheumatism].

Approximately 5% of patients with psoriasis develop chronic inflammatory joint disease which is clearly differentiated from rheumatoid arthritis by several features; absence of prevalence in females, elective involvement of distal joints of hands and feet, negative serologic tests, usually less severe outcome and absence of systemic manifestations. Conversely, psoriatic rheumatism resembles ankylosing spondylitis inasmuch as mainly sacroiliac but also vertebral involvement is common, with, in some instances, development of a typical pelvispondylitis. Thus, psoriatic rheumatism belongs to the group of seronegative spondylarthropathies. The genetic background of psoriatic rheumatism, with the exception of predominantly axial forms which are related to HLA B27, is very similar to that of isolated psoriasis, typified in particular by the frequency of HAL B17, B13 and B38. The immunologic disorders described in psoriasis and, more recently, in psoriatic rheumatism suggest that an immunologic dysfunction probably plays a significant part in the genesis of both conditions; however, the reasons why only a small proportion of patients with psoriasis develop joint disease remain obscure.