What is the treatment for inclusion body myositis?

Treatment for Inclusion Body Myositis

Currently, there is no known effective treatment for reversing or minimizing the progression of inclusion body myositis (IBM). 1 Despite numerous clinical trials testing various therapeutic approaches, no reliable effective therapy exists for this condition.

Disease Overview

Sporadic inclusion body myositis (sIBM) is distinctive among the idiopathic inflammatory myopathies with the following characteristics:

• Symmetric or asymmetric weakness of insidious onset
• Affects both proximal and distal muscles
• Typically occurs after age 50 years
• Male to female ratio of 3:1
• Classic atrophy of forearm flexors, finger flexors, and quadriceps muscles
• Dysphagia may be a prominent feature
• Minimally elevated muscle enzyme levels (CK)
• Muscle biopsy shows inflammatory mononuclear cell infiltrate with rimmed vacuoles and congophilic deposits 2

Treatment Approaches and Evidence

Immunosuppressive Therapies

1. Corticosteroids and Traditional Immunosuppressants

   • Not effective for IBM: Unlike other inflammatory myopathies, IBM typically does not respond to corticosteroids or conventional immunosuppressive agents 2
   • Trials of methotrexate have provided moderate-quality evidence that it does not arrest or slow disease progression 1
   • Azathioprine combined with methotrexate has been studied, but conclusive evidence of benefit is lacking 1

2. Intravenous Immunoglobulin (IVIG)

   • Multiple trials have compared IVIG to placebo, but meta-analysis has not been possible due to variations in study analysis and data presentation 1
   • Some transient improvements in swallowing function have been reported, but no consistent benefit for muscle strength has been demonstrated

3. Anti-T Lymphocyte Immunoglobulin (ATG) with Methotrexate

   • Very low-quality evidence from one open trial suggested some benefit of combined ATG and methotrexate therapy compared to methotrexate alone 1
   • This remains an experimental approach not widely adopted in clinical practice

Other Therapeutic Approaches

1. Biologic Agents

   • Interferon beta-1a has shown no important difference in muscle strength compared to placebo in pooled data from two trials 1
   • Rituximab has been studied in refractory cases but without conclusive evidence of benefit

2. Anabolic Steroids

   • Oxandrolone has been studied, but data do not allow for definitive conclusions about its efficacy 1

3. Novel Agents

   • Arimoclomol (targets protein misfolding) and bimagrumab (activates muscle growth) have been investigated in clinical trials, but complete analyses are pending 1
   • Simvastatin studies are ongoing

Management Approach

Given the lack of disease-modifying treatments, management focuses on:

1. Supportive Care

   • Physical therapy to maintain mobility and prevent contractures
   • Occupational therapy for adaptive strategies and assistive devices
   • Swallowing evaluation and dietary modifications for dysphagia

2. Dysphagia Management

   • Critical for preventing aspiration pneumonia
   • May require feeding tube placement in advanced cases

3. Experimental Treatments

   • Consider referral to specialized centers conducting clinical trials
   • Enrollment in research studies may provide access to novel therapies

Common Pitfalls and Caveats

1. Misdiagnosis as Polymyositis

   • IBM is frequently misdiagnosed as polymyositis and inappropriately treated with steroids 3
   • Treatment-resistant "polymyositis" in patients over 50 years should raise suspicion for IBM 3

2. Delayed Diagnosis

   • Slow progression of the disease often leads to delayed diagnosis 3
   • Characteristic pattern of weakness (finger flexors, quadriceps) should prompt consideration of IBM

3. Unrealistic Expectations

   • Patients should be counseled that current treatments do not halt disease progression
   • Focus should be on maintaining function and quality of life

4. Overreliance on CK Levels

   • CK levels may be only minimally elevated in IBM, unlike other inflammatory myopathies 2

Future Directions

Research is ongoing into novel therapeutic approaches targeting both inflammatory and degenerative aspects of IBM:

• Targeting protein misfolding and aggregation
• Enhancing muscle regeneration
• Modulating specific immune pathways

Until effective treatments are developed, management should focus on supportive care, symptom management, and maintaining quality of life through multidisciplinary care.