The Lack of Rheumatoid Factor in Psoriatic Arthritis

Summary104 cases of psoriasis arthropathy were compared serologically with 140 cases of rheumatoid arthritis and with 80 cases of uncomplicated psoriasis. Rheumatoid factor was present much more seldom in cases of P.A. than in R.A. and could be demonstrated in only one case of uncomplicated psoriasis. Study of the occurrence of rheumatoid factor in association with various types of roentgenological abnormalities showed that cases of psoriasis with typically localized erosions in the distal joints of the fingers and/or the interphalangeal joints of the lateral toes, with at the same time a total lack of rheumatoid factor, can be classified as psoriatic arthritis. Additional studies are required to throw light on the cause of the low values of macroglobulins in psoriasis.