Does previous corticosteroid treatment affect the inflammatory infiltrate found in polymyositis muscle biopsies?

The aim of the study was to evaluate the effect of the prior use of corticosteroids (CS) on the presence of inflammatory infiltrates (InI) in muscle biopsies of polymyositis (PM).

We retrospectively evaluated 60 muscle biopsy samples that had been obtained at the time of the diagnosis of PM. The patients were divided into three groups according to the degree of the InI present in the muscle biopsies: (a) minimal InI present only in an interstitial area of the muscle biopsy (endomysium, perimysium) or in a perivascular area; (B) moderate InI in one or two areas of the interstitium or of the perivascular area; and (C) moderate InI throughout the interstitium or intense inflammation in at least one area of the interstitium or of the perivascular area.

The three groups were comparable regarding the demographic, clinical and laboratory features (p>0.05). Approximately half of the patients in each group were using CS at the time of the muscle biopsy. The median (interquartile) duration of CS use [4 (0-38), 4 (0-60) and 5 (0-60) days: groups A, B and C, respectively] and the median cumulative CS dose used [70 (0-1200), 300 (0-1470) and 300 (0-1800)mg] were similar between the groups (p>0.05).

Previous CS use did not influence the presence or the degree of InI found in muscle biopsies in PM with clinical and laboratory disease activity. Our study showed that muscle biopsies should be performed this population, even in individuals who have already been taking CSs.