Involvement of the inconstant bursa of the fifth metatarsophalangeal joint in psoriatic arthritis: a clinical and ultrasonographic study.

The bursa of the 5th metatarsophalangeal joint appears to be involved in PsA more frequently than by chance. If confirmed by other studies, this finding could be considered as a distinctive clinical sign of PsA, useful for differential diagnosis with the other SpA. In asymptomatic patients, US proved to be more sensitive in the detection of bursitis.