Sporadic Inclusion Body Myositis: A Clinicopathological Study

Background: Sporadic inclusion body myositis (s-IBM) is rare in India.

Aim: The aim of this study was to diagnose s-IBM according to the European Neuromuscular Center (ENMC) IBM research diagnostic criteria 2011.

Materials and methods: A retrospective review of patient records diagnosed as s-IBM according to the above criteria during the period from January 2010 to May 2015 was done with an emphasis on pattern of muscle weakness.Serumcreatine kinase (CK) andelectromyography (EMG) were noted. Muscle biopsy was evaluated with basic panel of histochemical stains including Congo red stain. Immunohistochemistry (IHC) with ubiquitin was done in 10 biopsies. IHC for major histocompatibility complex-1 and electron microscopy studies were not performed.

Results: The diagnosis of s-IBM constituted 5 clinicopathologically defined, 12 clinically defined, and 10 probable IBM in the study period. There was male predominance with median age at 51 and duration of disease varying from 1-5 years. All the patients presented with insidious onset of muscle weakness of quadriceps and/or forearm flexors. CK varied from 57-2939 IU/L. EMG was myopathic in 22, mixed in 2, and neuropathic in 3. Endomysial inflammation was seen in 23 (85.19%) and rimmed vacuoles in 24 (88.89%). Amyloid was demonstrated in only 5 (18.52%) and ubiquitin in 2 biopsies. Mitochondrial abnormalities were seen in 92.59% biopsies.

Conclusions: Application of the ENMC IBM research diagnostic criteria allowed diagnosis of clinically-defined and probable IBM in the absence of all pathology criteria. Rimmed vacuoles in 88.89% of biopsies indicate presentation at a late stage. Use of ancillary techniques can improve diagnostic yield.