Sporadic inclusion body myositis: Clinical, pathological, and genetic analysis of eight Polish patients

Abstract

Introduction: Sporadic inclusion body myositis (sIBM) is one of the most common myopathies in patients above 50 years of age. Its progressive course finally leads to immobilisation, and no effective therapy exists. Its pathogenesis includes both degenerative and inflammatory processes, however, its direct causes remain unknown. Therefore, a possible genetic background of the disease must also be considered. Material and methods: Here we report on twelve patients: eight with sporadic inclusion body myositis and four with other myopathies with rimmed vacuoles in muscle biopsy. All patients were evaluated clinically, morphologically, radiologically, and genetically. Results: All patients with sIBM presented both shoulder and pelvic girdle muscle involvement. In addition, distal upper and lower limb muscle weakness was noted. Patients with other muscle disorders showed effects mainly in proximal muscles and marked calf muscle hypertrophy. In sIBM cases computed tomography of lower limb muscles revealed atrophy that was most pronounced within the quadriceps femoris and gracilis muscles in the thighs and within the medial head of the gastrocnemius muscle and the tibialis anterior muscle in the lower legs. On light microscopy mononuclear cell invasion of muscle flbres was present in six patients with sIBM. On electron microscopy myofibrillar disorganisation and mitochondrial abnormalities were noted in all sIBM patients, whereas cytoplasmic tubulofilamentous inclusions were seen in three patients and both cytoplasmic and nuclear inclusions in one of them. According to the criteria by Rose et al. (2011) six patients were classified as "clinico-pathologically defined IBM", one as "clinically defined IBM", and one as "probable IBM". Pathological deposits of TDP-43 were found in muscles in all sIBM as well as in control cases. Additionally, accumulation of other proteins thought to be associated with sIBM, like β-amyloid, α-synuclein, and tau protein, was present in the most of examined biopsies. All twelve patients were screened for the presence of causative mutations in TARDBP, VCP, HNRNPA1, and HNRNPA2B1 genes. Additionally, analysis of C9ORF72 hexanucleotide repeat expansion was performed. No causative mutations were found in any of the patients. Conclusions: Our study provides the first - to our knowledge - comprehensive clinical, pathological, and genetic workup of a group of Polish patients.