Inclusion body myositis (IBM)

Inclusion body myositis (IBM) is a complex disorder of unknown aetiology, where inflammation and autoimmunity against muscle fibres coexists with features of degeneration

• histologically
  • characterized by the presence of endomysial CD8 inflammatory cells surrounding myofibres and rimmed vacuoles, and an abnormally elevated number of cytochrome oxidase-negative fibre

Clinical features:

• slowly progressive degenerative inflammatory disorder affecting both proximal and distal muscles, resulting in substantial weakness and atrophy
• may affect axial muscles, resulting in camptocormia or head-drop
• at late-stage disease
  • pharyngeal muscles could be affected, leading to life-threatening dysphagia and aspiration pneumonia and finally death.

Management:

• some patients might initially respond to steroid therapy; however, the large majority remains resistant
• immunosuppressive therapies, including methotrexate, cyclosporine, azathioprine or mycophenolate mofetil, are largely ineffective in patients with IBM
• immunoglobulin therapy has been used in these patients with some positive results

Reference:

• Dalakas MC. Sporadic inclusion body myositis - diagnosis, pathogenesis and therapeutic strategies. Nat Clin Pract Neurol. 2006;2:437-447
• Needham M, Mastaglia FL. Sporadic inclusion body myositis: a continuing puzzle. Neuromuscul Disord. 2008;18:6-16.