Subclinical enthesopathy of the midfoot: could it be a peculiar feature in early psoriatic arthritis?

Objectives Bone scintigraphy (BS) is a sensitive tool that provides functional imaging to evaluate bone abnormalities in psoriatic arthritis (PsA). Our aims were to analyse the prevalence of increased BS uptake in the midfoot of PsA patients and to evaluate whether BS midfoot abnormalities could herald ultrasonography (US) and x-ray lesions in the same site. Methods Out of 88 consecutive BS performed in patients with early musculoskeletal symptoms (January-December 2010) and retrospectively analysed, 32 exams were carried out on subjects 3 months after being diagnosed with PsA. These patients were included in a retrospective study and analysed for BS feet uptake. Their baseline x-rays of the feet were also retrieved. Five years after BS (January-December 2015) all 32 PsA patients underwent clinical evaluation, x-rays and US of the feet. Frequency and percentage of each imaging abnormality of the midfoot were analysed. Clinical, functional and laboratory indexes were collected and correlations between clinical and imaging parameters were studied. Results Of all 32 PsA patients, 21 (65.6%) had an increased BS uptake in the midfoot, without any baseline x-ray abnormalities. After 5 years, the x-rays and US were able to detect ≥1 lesion in the midfoot of 14/32 (43.8%) and 28/32 (87.5%) patients, respectively. A high prevalence of enthesophytes in all 64 midfeet was shown by both x-rays (40.6%) and US (81.6%). We found a higher prevalence of structural lesions in the subgroup with BS positive midfoot compared with BS negative patients: x-rays [10/21 (47.6%) vs. 4/11 (36.4%); p=0.04] and US [19/21 (90.5%) vs. 8/11 (72.7%); p=0.04]. Conclusions Midfoot involvement is frequent in PsA. BS increased uptake in the midfoot seems to be an early sign of the disease.