In a small percentage of psoriatic patients, there is involvement of the joints resembling rheumatoid arthritis. This combination is termed psoriasis arthropathica.
The joints of the fingers, feet, ankles, knees and sacro-iliac are selectively affected; these joints are swollen and painful.
The psoriatic eruption and the involvement of the joints may increase or decrease simultaneously. Nail changes are usually present.
Radiological changes are characteristic and consist of osteoporosis followed by increased density, diminished joint space, erosion of joint surfaces followed by eventual destruction of the ends of bones. Ultimately, the joints become deformed.