Inclusion body myositis in French patients. A clinicopathological evaluation

Abstract

In order to establish the frequency of inclusion body myositis (IBM) in a European neuropathological unit and to evaluate the specificity of IBM pathology, we reviewed the 850 muscle biopsies performed in our laboratory over the past 7 years. Clinical histopathological and ultrastructural evaluation of all cases showing rimmed vacuoles, a constant histopathological feature of IBM, was done and the diagnosis of IBM was assessed using the clinico-pathological criteria of Calabrese, Mitsumoto & Chou (1987). Among the nine cases showing rimmed vacuoles, five were classified as IBM (group 1), either definite (3/5) or probable (2/5), and four suffered from a chronic denervating process of muscle (group 2). The overall frequency of IBM (06% of all muscle biopsies) was similar to that reported by North American authors. IBM represented 16% of adult idiopathic inflammatory myopathies investigated in our laboratory. Clinical and histopathological findings in group 1 were homogeneous and distinctive. Muscle biospy was consistent with an inflammatory myopathy in all patients in group 1 and with a non-inflammatory denervating process in 3/4 patients in group 2. Typical intrasarcoplasmic inclusions were detected by electron microscopy in 3/5 cases in group 1 and 1/4 in group 2, which raises questions about the specificity of the 16 18 nm tubulofilaments. Failure to demonstrate inclusions in two patients with otherwise typical IBM, was probably related to the paucity of rimmed vacuoles observed in these cases.