Ultrasound imaging for the rheumatologist XXXII. Sonographic assessment of the foot in patients with psoriatic arthritis

Psoriatic arthritis (PsA) is an arthropathy associated with psoriasis, which is part of the spondyloarthropathy family, and which may present with various forms, from mono-oligoarthritis to symmetric polyarthritis mimicking rheumatoid arthritis. In longstanding disease, the symmetric polyarthritis is the most common pattern of PsA, involving the small joints of hands, feet (the involvement of which seems to be very common, ranging from 50 to 100% of patients), wrists, ankles and knees. Other common features are represented by the inflammation of enthesis and tendons. Its exact prevalence, in Italy, should be about 30% in psoriatic subjects or 0.42% when considering the general population. The aims of our study were to investigate, by US examination, the prevalence and the features of foot involvement in PsA and to describe their correlations with clinical findings. Ultrasound (US) examinations were performed using a Logiq 9 (General Electric Medical Systems, Milwaukee, WI) equipped with a multifrequency linear probe, working at 14 MHz. One hundred and eighty feet were investigated in a total of 101 patients. Prior to US assessment, all patients underwent a clinical examination by an expert rheumatologist who recorded the presence/absence of pain, tenderness (detected by palpation and/or active or passive mobilisation of the feet) and swelling. US finding indicative of metatarsophalangeal joint inflammation were obtained in 77 (76.2%) patients, while only 34 (33.7%) patients were positive to the clinical examination. This study demonstrates that US detected a higher number of inflamed joints with respect to clinical assessment in PsA patients.