Treatment of inclusion body myositis.

Sporadic inclusion body myositis (s-IBM) is considered the most common muscle disease in patients older than 50 years, with a male predominance. Features of s-IBM include insidious onset, slowly and relentlessly progressive muscle weakness, a characteristic distribution and atrophy of both the proximal and distal muscle groups, and resistance to immunosuppressive drugs. The most characteristic pathologic feature is vacuolar degeneration of muscle fibers accompanied by intrafiber congophilia and clusters ("tangles") of paired-helical filaments, containing phosphorylated tau. The response of s-IBM to immunotherapy remains controversial. Some reports emphasized partial improvement in early stages of the disease. However, the lack of clear response to corticosteroids and immunosuppressive therapies, the deterioration of clinical strength despite suppression of inflammation but increasing number of fibers with vacuoles and amyloid deposits under therapy, and the accumulation of "Alzheimer-characteristic" proteins in vacuolated muscle fibers suggest that s-IBM may be a degenerative rather than an auto-immune inflammatory myopathy, and a secondary inflammation response.