Inclusion body myositis
Inclusion body myositis is a sporadic inflammatory myopathy of older adults that breaks the pattern of the other myositides: it favors men, causes insidious, often asymmetric weakness of the finger flexors and quadriceps plus dysphagia, and raises creatine kinase only mildly. Biopsy shows endomysial inflammation with rimmed vacuoles and congophilic amyloid inclusions. It does not respond to glucocorticoids or immunosuppression, so treatment centers on structured exercise and physical therapy, dysphagia evaluation and swallowing therapy, and falls prevention.
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What this article covers
- Overview
Definition: inclusion body myositis (IBM) is a sporadic idiopathic inflammatory myopathy (IIM) that combines an endomysial T-cell inflammatory infiltrate with a degenerative, protein-aggregating process in muscle fibers.
- Epidemiology
Age: IBM occurs in persons older than 50 years and mainly in patients older than 60, unlike the bimodal childhood/mid-40s-to-50s onset of dermatomyositis.
- Risk factors
Age over 50, particularly over 60: the dominant demographic risk factor; IBM is essentially a disease of later life.
- Pathophysiology
Endomysial T-cell attack: as in polymyositis, CD8-positive cytotoxic T cells localize within the endomysium, surrounding and invading nonnecrotic muscle fibers that express major histocompatibility complex class I.
- Clinical features
Insidious, slowly progressive course: weakness develops over years, unlike the acute-to-subacute onset of polymyositis, dermatomyositis, and immune-mediated necrotizing myopathy.
- Differential diagnosis
Polymyositis: proximal weakness, but acute-to-subacute, symmetric, higher creatine kinase, and typically improves with glucocorticoids, unlike IBM.
- Diagnosis
The diagnosis rests on the classic clinical pattern and, when needed, muscle biopsy: the 2017 European League Against Rheumatism/American College of Rheumatology criteria first estimate the…
- Management
First, confirm the diagnosis rather than escalate an ongoing trial: IBM usually does not respond, so a course started for presumed refractory polymyositis should be reassessed, not escalated, since…
- Complications
Progressive functional decline: slow, relentless loss of strength that over 10 to 15 years requires assistive devices and, in many patients, a wheelchair.
- Prognosis
Slow and relentless: lacking effective disease-modifying treatment, IBM progresses to wheelchair dependence within 10 to 15 years of symptom development.
- Prevention
No primary prevention exists: IBM is sporadic with no confirmed trigger, so care focuses on limiting functional loss and its complications.
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