Inclusion body myositis

Abstract

Inclusion body myositis is the most common type of late-onset inflammatory myopathy Inclusion body myositis is an idiopathic inflammatory myopathy. Whether its cause is primarily autoimmune or degenerative is debated. Its prevalence is 18 per 100 000 people, higher than dermatomyositis or amyotrophic lateral sclerosis (ALS). Inclusion body myositis predominantly affects males (3:1 to females), usually becoming symptomatic after age 50 years. 1 2 Typical features are insidious, painless, and progressive weakness and muscle atrophy that is asymmetric and multifocal Inclusion body myositis affects proximal and distal muscles, causing striking weakness of the quadriceps and finger flexor muscles. 2 This leads to falls and loss of grip strength. Over time, foot drop and dysphagia also become prominent.3 Electromyography (EMG) and muscle biopsy are the leading diagnostic tools Serum levels of creatinine kinase are only moderately elevated at 300-2000 U/L. Needle EMG may show equivocal findings that can suggest both myopathy and neuropathy. Current auto-antibody tests (anti-NT5C1A) have high specificity (90%) but only moderate sensitivity (40%); results must be interpreted in the clinical context. 3 A muscle biopsy should be performed, which may reveal inflammation, rimmed vacuoles, and congophilic inclusions; interpretation requires expertise in neuromuscular pathology. 4