From the Guidelines
Polymyositis, a rare but potentially life-threatening condition, should be treated with high-dose corticosteroids such as prednisone (starting at 0.5-1 mg/kg/day) as the first line of treatment, according to the most recent and highest quality study 1.
Treatment Approach
The treatment approach for polymyositis involves:
- High-dose corticosteroids as the initial treatment
- Immunomodulatory treatment, such as intravenous immunoglobulin (IVIG) and/or plasma exchange, for patients with bulbar symptoms, dyspnoea, and/or myocarditis
- Consideration of IL-6R inhibitors and TNF-a inhibitors in refractory cases
- Discontinuation of ICI treatment for grade 2 symptoms
Diagnostic Evaluation
Diagnostic evaluation for polymyositis should include:
- Myositis-associated autoantibodies
- MRI
- Electromyogram (EMG) biopsy
- Monitoring of muscle enzymes like creatine kinase (CK) to track disease activity and treatment response
Disease Characteristics
Polymyositis is characterized by:
- Muscle weakness affecting both sides of the body, particularly in the shoulders, hips, and thigh muscles
- Inflammation of muscle fibers, leading to their destruction as the body's immune system inappropriately attacks healthy tissue
- Potential for severe and fatal complications, including rhabdomyolysis and myocardial inflammation
Treatment Goals
The primary goals of treatment for polymyositis are to:
- Reduce muscle inflammation and damage
- Improve muscle strength and function
- Prevent long-term complications and mortality
- Minimize treatment-related side effects and improve quality of life, as supported by the study 1.
From the Research
Treatment Options for Polymyositis
- The first line of therapy for polymyositis consists of high-dose oral prednisone, prescribed at 1mg/kg/day, then progressively tapered based on patients' clinical response 2.
- In patients who do not improve with corticosteroids alone, methotrexate is added, with the therapeutic effect observed within 8 weeks 2.
- If patients are refractory to corticosteroids and methotrexate, intravenous immunoglobulins can be added 2.
- Other therapeutic agents that may be proposed for patients who fail to respond to the initial therapeutic strategy include mycophenolate mofetil and rituximab 2, 3, 4.
Immunotherapy in Polymyositis
- A systematic review of the evidence for immunotherapy in the treatment of dermatomyositis and polymyositis found that improved outcomes were demonstrated with a number of agents, including methotrexate, azathioprine, ciclosporin, rituximab, and intravenous immunoglobulin 5.
- Plasmapheresis and leukapheresis were found to be of no apparent benefit 5, 6.
- Anti-TNF agents are not recommended for use in polymyositis patients, as they have been shown to favor exacerbation of interstitial lung disease and myositis and increase the risk of severe pyogenic and opportunistic infections 2.
Management of Steroid Resistance
- For patients insufficiently responding to corticosteroids, immunosuppressants such as azathioprine, mycophenolate, methotrexate, or cyclosporine may be used, although they provide minimal benefit on their own 4.
- Intravenous immunoglobulin (IVIg) is a second-line therapy that has been shown to be effective in many patients with polymyositis 4.
- Rituximab and tacrolimus may offer additional benefit for patients with steroid-resistant polymyositis 4.