Peritenon extensor tendon inflammation at metacarpophalangeal joints level: a valuable ultrasound finding in the differential diagnosis between psoriatic arthritis and rheumatoid arthritis?

PTI was found more frequently in PsA rather than in RA patients. Nevertheless, since no statistically significant difference was found between RA and PsA patients with less than 1 year of disease duration, PTI may represent an inflammatory feature of the early phases of both the diseases.