Most common muscle disease in patients older than 50 years. More common in white men, but can affect any group
Thought to be degenerative, rather than auto-immune. Associated with systemic autoimmune or connective-tissue diseases in up to 15 %
Difficulty with everyday tasks predominantly requiring the use of proximal muscles, such as getting up from a chair, climbing steps, stepping onto a curb, lifting objects, or combing their hair
Fine-motor movements that depend on the strength of distal muscles (especially foot extensors and finger flexors), such as buttoning a shirt, sewing, knitting, or writing, are affected fairly early in the course
The pharyngeal and neck-flexor muscles are often involved, causing dysphagia or fatigue and difficulty in holding up the head
May also progress slowly for years, and its clinical features may simulate those of limb-girdle muscular dystrophy.
Consider IBM in patients with polymyositis or dermatomyositis that is resistant to treatment.
Muscle strength – myopathic muscle weakness with early involvement of the distal muscles
EMG – myopathic with mixed potentials
Muscle enzymes – normal or elevated
Muscle biopsy – definitive
Light microscopy — endomysial inflammation, rimmed vacoules distributed around the edge, eosinophilic cytoplasmic inclusions
EM — granules contain membranous whorls. Filamentous inclusions in the cytoplasm or nucleus, prominent in the vicinity of the rimmed vacuoles, are pathognomonic
Inclusion-body myositis is generally resistant to all therapies, and its rate of progression also appears to be unaffected by treatment.