The therapeutic dilemma of inclusion body myositis

Abstract

Inclusion body1 myositis (IBM) has unique clinical, histologic, and therapeutic features that distinguish it from other inflammatory myopathies, particularly polymyositis and dermatomyositis. [1-3] Although similar but noninflammatory familial forms are recognized, this editorial is concerned with only the sporadic form of the disease. IBM patients develop slowly progressive weakness, usually after the age of 50. The slow evolution of the disease is one of the primary reasons for the delay in diagnosis, which averages approximately 6 years from the onset of symptoms. [1] Men are much more commonly affected than women. The clinical hallmark of IBM is early weakness and atrophy of the quadriceps, wrist and finger flexors, and ankle dorsiflexors. Severe weakness in these muscle groups is so characteristic of IBM, that even if the classic histologic findings are not present on muscle biopsy, a presumptive diagnosis of possible IBM should be considered. [1,2] Classic light microscopy features are endomysial inflammation with invasion of non-necrotic muscle fibers, eosinophilic cytoplasmic inclusions, and rimmed vacuoles within the muscle fibers that contain amyloid deposits. [4] Electron microscopy reveals an accumulation of cytoplasmic and intranuclear 15- to 21-nm tubofilaments. The inflammatory response consists of macrophages and CD8 sup + cytotoxic/suppressor T lymphocytes and is often the most prominent initial histologic finding. [5] The other pathologic features may not be identified on the initial muscle biopsy, often necessitating second or third biopsy for confirmation. Despite the inflammatory response …