What is the treatment for inclusion body myositis?

Treatment for Inclusion Body Myositis

There is currently no known effective treatment for reversing or minimizing the progression of inclusion body myositis (IBM), and management focuses on supportive care including monitoring of swallowing and respiratory function, adapting exercise routines, and addressing mobility issues. 1

Disease Characteristics

• IBM is a late-onset inflammatory muscle disease characterized by symmetric or asymmetric weakness of insidious onset involving proximal and/or distal muscles, typically occurring after age 50 years with a male to female ratio of 3:1 2
• Classic features include atrophy of the forearm flexors, finger flexors, and quadriceps muscles, with dysphagia being a prominent feature that can lead to poor outcomes such as feeding tube placement or recurrent aspiration pneumonia 2
• Muscle enzyme levels, such as creatine kinase (CK), may be minimally elevated, and muscle biopsy reveals inflammatory mononuclear cell infiltrate with rimmed vacuoles and congophilic deposits 2
• IBM has pathologic features suggesting a degenerative neuromuscular disease with muscle fiber vacuolization and abnormal accumulation of amyloid-β and phosphorylated tau proteins 2, 3

Diagnostic Approach

• Diagnosis criteria include duration of illness longer than 6 months; age at onset older than 30 years; weakness of proximal and distal muscles with finger flexor weakness, wrist flexor greater than wrist extensor weakness, or quadriceps weakness; serum CK level less than 12 times normal; and characteristic muscle biopsy findings 2
• Laboratory evaluation should include muscle enzymes (CK, aldolase), inflammatory markers (ESR, CRP), and myositis-specific autoantibodies 3
• MRI can identify muscle inflammation and guide biopsy site selection 3
• EMG may show polyphasic motor unit action potentials of short duration and low amplitude with increased insertional and spontaneous activity 3

Treatment Options and Evidence

• Multiple clinical trials have failed to identify effective disease-modifying treatments for IBM 1, 4
• Moderate-quality evidence from clinical trials shows that interferon beta-1a and methotrexate have no effect on the progression of IBM 4
• Very low-quality evidence from an open trial suggested that anti-T lymphocyte immunoglobulin (ATG) combined with methotrexate might be more effective than methotrexate alone 4
• Trials of intravenous immunoglobulin (IVIg), oxandrolone, and azathioprine plus methotrexate have provided inconclusive results 4
• Studies of simvastatin and bimagrumab (BYM338) are ongoing, and complete analysis of arimoclomol effects is pending 4

Management Approach

• The mainstay of management includes close monitoring of swallowing and respiratory function 1
• Adapting appropriate exercise routines is recommended to maintain function 1
• Addressing mobility issues through physical therapy and assistive devices is important 1
• Treatment challenges in elderly patients include increased risk of complications from immunosuppressive therapy, requiring careful monitoring 3

Prognosis and Complications

• IBM leads to severe disability, and most patients eventually lose ambulation due to lack of curative or disease-modifying treatment options 5
• Factors associated with poorer outcomes include advanced age, presence of dysphagia, cardiac involvement, and associated malignancy 3
• The disease is often underdiagnosed or misdiagnosed as polymyositis, leading to inappropriate treatment with steroids 6
• Treatment-resistant "polymyositis" in patients over 50 years of age is often IBM 6

Future Directions

• Current research focuses on enhancing understanding of pathogenesis and developing new therapeutic approaches 7
• Obstacles to effective treatment include variability in presentation, diagnostic challenges, poor understanding of pathogenesis, scarcity of disease models, lack of validated outcome measures, and challenges related to clinical trial design 1