The idiopathic inflammatory myopathies (IIM) in adults are a heterogenic group of disorders characterized by muscle inflammation and progressive muscle weakness. IIM is composed of polymyositis (PM) which is extremely rare, (clinically amyopathic) dermatomyositis (DM), nonspecific or overlap myositis (NSM/OM), and necrotizing autoimmune myopathy (NAM) which have a subacute onset, and chronic sporadic inclusion body myositis (IBM).
Oral high dose (1-1.5 mg/kg) prednisone is the mainstay of treatment in (sub)acute IIM. After 4-6 weeks the dose is usually tapered off over the course of 1-1.5 year. This treatment causes considerable adverse effects with long-term use, and often relapses occur during tapering. Monthly pulsed therapy with dexamethasone may be an alternative since this intervention was equally effective but patients experienced fewer side effects. Immunosuppressive agents, such as azathioprine or methotrexate are often used in case of relapse, as steroid-sparing agent, or in case of rapidly progressive disease. However no trials have shown the superiority of one agent over the other. In patients with refractory or severe disease intravenous immunoglobulin (IVIG), intravenous methylprednisolone, rituximab or enteracept can be considered, albeit the evidence is not very solid.
Recently, a potential novel treatment of IBM was reported. A single dose of intravenously administered bimagrumab was found to increase thigh muscle volume at 8 weeks, and showed trends in improvement for strength and function during the subsequent 24 weeks of observation.
Disclosure of Interest None declared