What is inclusion body myositis (IBM)?
Inclusion body myositis is the most common cause of acquired chronic myopathy in patients age 50 years and older.
Characteristically, there is insidious onset of painless weakness and atrophy involving the quadriceps, finger flexors, and foot dorsiflexors.
Dysphagia is common. There is early loss of patellar reflexes, and a mild neuropathy may be present. CK levels are either normal or only mildly elevated. Electrodiagnostic evaluation reveals mixed myopathic and neurogenic changes.
Muscle biopsy shows invasion of nonnecrotic fibers by mononuclear cells, cytoplasmic “rimmed” vacuoles and eosinophilic inclusion bodies, and small angular atrophic and denervated fibers sometimes with mitochondrial dysfunction.
Despite the evident inflammation, Inclusion body myositis is resistant to conventional immunotherapies and is felt to be more likely a myodegenerative condition.
One-third of cases appear stable or show improvement for periods of 6 months or more.
Cricopharyngeal myotomy might be beneficial in cases of dysphagia and might delay the need for a percutaneous endoscopic gastrostomy.
