School of Medicine

Introduction : Sporadic inclusion body myositis (sIBM) is the most common myopathy in people over 40 years of age. However, sIBM is a poorly understood disease with no effective treatments to date. Currently there are no reliable animal models for sIBM which is a hindrance to development of new therapies. While other inflammatory myopathies are well documented in dogs, spontaneously occurring sIBM was only recently reported (Shelton et al. 2009). The identification of sIBM in dogs raises the possibility that canine sIBM may be a useful animal homologue for the comparable human disease. As sIBM is associated with aging, and baseline information on normal aged canine muscle not available, in-depth studies of normal aging changes in canine muscle were performed. Methods : Fresh frozen muscle biopsies from five aged dogs (>10 years) without clinical signs of neuromuscular disease were sectioned and examined by light microscopy using a standard panel of histologic stains and enzyme reactions. The following histologic features were observed and quantitated morphometrically using NIH Image software : (1) variability in myofiber diameter, (2) fiber type proportions, (3) ratio of capillaries to muscle fibers, and (4) percentage of muscle area composed of endomysial connective tissue. Discussion : This study provided baseline data that will help characterize normal aged canine muscle. Future studies will compare normal aged canine muscle to normal young adult (< 5 years) canine muscle, and to the muscle of aged dogs with suspected sIBM. Together these studies will provide useful baseline data for interpretation of muscle changes in future studies of canine sIBM and other myopathies associated with aging. Ultimately, the goal is to establish the dog as a reliable homologue for sIBM, and facilitate research into the pathogenesis and potential treatments of sIBM.