Inclusion body myositis

Inclusion body myositis (IBM), also known as sporadic inclusion body myositis (sIBM), is the most common acquired inflammatory myopathy in adults over the age of 50. It is a chronic, progressive muscle disease characterized by slowly worsening muscle weakness and wasting (atrophy). IBM primarily affects the skeletal muscles, with a distinctive pattern of involvement that preferentially targets the quadriceps (thigh muscles), deep finger flexors, wrist flexors, and ankle dorsiflexors. This pattern leads to characteristic clinical features including difficulty gripping objects, frequent falls due to knee buckling, foot drop, and trouble swallowing (dysphagia), which occurs in a significant proportion of patients. The disease is distinguished from other inflammatory myopathies by the presence of characteristic pathological findings on muscle biopsy, including rimmed vacuoles, endomysial inflammatory infiltrates predominantly composed of CD8+ T cells, and inclusions containing aggregated proteins such as amyloid-beta, phosphorylated tau, and TDP-43. The pathogenesis of IBM involves both inflammatory/autoimmune and degenerative mechanisms, and the relative contribution of each remains an area of active research. Serum creatine kinase (CK) levels are typically mildly to moderately elevated. Anti-cytosolic 5'-nucleotidase 1A (anti-cN1A) antibodies are found in approximately 30-60% of patients and can support the diagnosis. Unlike other inflammatory myopathies such as polymyositis and dermatomyositis, IBM is notably resistant to immunosuppressive therapies including corticosteroids, intravenous immunoglobulin (IVIg), and other immunomodulatory agents. No pharmacological treatment has been proven to halt or reverse disease progression. Current management is primarily supportive and includes physical therapy to maintain function and mobility, occupational therapy for adaptive strategies, speech and swallowing therapy for dysphagia, and assistive devices as needed. The disease progresses slowly over years to decades, eventually leading to significant disability, with many patients requiring a wheelchair within 10-15 years of symptom onset.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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