Inclusion body myositis (IBM) is a chronic, acquired inflammatory myopathy with typical clinical symptoms and characteristic histopathological features in muscle biopsy. However, there are still uncertainties in diagnostic criteria, implying that disorders of potentially different origin may be classified as IBM. In particular, muscle biopsy findings of vacuolar myopathy in Sjögren's syndrome have indicated an association with IBM, and so far vacuolar Sjögren myopathy is included in the IBM entity.
We therefore compared clinical and histopathological features in a group of patients with sporadic-IBM (s-IBM, n=11) with a group of patients with primary Sjögren's syndrome (pSS) with IBM-like findings in their muscle biopsies (n=10). Biopsies from s-IBM but not from Sjögren patients stained for Congo-red, whereas no other obvious differences were fonnd concerning morphological or biochemical fmdings of vacuolar content (hyperphosphorylated tau-protein: SMI 31 and SMI 310, ubiquitin, tau-protein, ß-amyloid, ß-amyloid precursor protein). Striking differences were fonnd in the clinical picture, age of onset and gender preponderance (females in pSS and males in s-IBM).
Based on the different clinical features and the difference in Congo-red staining, we suggest that vacuolar myopathy in pSS should be regarded as a separate entity, not to be included in the classical s-IBM group. IBM-like fmdings in muscle biopsy are observed in different types of systemic inflammatory diseases, and could preferably be designated as autoimmune associated IBM (a-IBM).