Initial Treatment for Myositis

Diagnostic Evaluation

A complete rheumatologic and neurologic examination, including muscle strength testing, is essential before initiating treatment, and should include laboratory evaluation of muscle enzymes and inflammatory markers, according to the Journal of Clinical Oncology 1
Laboratory evaluation should include muscle enzymes, such as CK, transaminases, LDH, and aldolase, as well as inflammatory markers, including ESR and CRP, as recommended by the Journal of Clinical Oncology 1
Cardiac evaluation with troponin and echocardiogram should be considered if myocardial involvement is suspected, as suggested by the Journal of Clinical Oncology 1

The American College of Rheumatology recommends beginning prednisone at 0.5-1 mg/kg per day, typically 60-80 mg daily, concurrently with a steroid-sparing immunosuppressive agent, such as methotrexate, azathioprine, or mycophenolate mofetil, to improve outcomes and reduce steroid-related side effects 2
Methotrexate is a recommended steroid-sparing agent, as suggested by the Journal of Clinical Oncology 1
Azathioprine is another option for a steroid-sparing agent, as recommended by Praxis Medical Insights 2
Mycophenolate mofetil is also a suitable option for a steroid-sparing agent, according to Praxis Medical Insights 2

For severe disease, the Journal of Clinical Oncology recommends prednisone 0.5-1 mg/kg/day, and considers high-dose methylprednisolone pulse therapy, as well as additional therapies such as cyclophosphamide, cyclosporine, and intravenous immunoglobulin (IVIG) 2
For immune checkpoint inhibitor-related myositis, the Journal of Clinical Oncology suggests holding immune checkpoint inhibitor therapy and resuming upon symptom control for grade 2 toxicity, and holding and potentially resuming in consultation with rheumatology for grade 3-4 toxicity 1
Approximately 10% of patients with immune checkpoint inhibitor-related myositis may require intravenous methylprednisolone pulses, as noted by Praxis Medical Insights 2

Regular monitoring of muscle enzyme levels, such as CK, and inflammatory markers, including ESR and CRP, is recommended by Praxis Medical Insights 2
MRI with T1-weighted, T2-weighted, and fat suppression techniques can help monitor treatment response, as suggested by Praxis Medical Insights 2

Failure to screen for malignancy in adult patients, especially with dermatomyositis, is a common pitfall, as noted by Praxis Medical Insights 2
Inadequate initial dosing of corticosteroids is another common pitfall, according to Praxis Medical Insights 2
Delaying initiation of steroid-sparing agents is also a common pitfall, as recommended by Praxis Medical Insights 2

Autoimmune tests should be performed as required for differential diagnosis, according to the American College of Rheumatology 3
EMG (electromyography) and/or MRI can be used to show muscle fibrillations or increased intensity and edema in affected muscles, as recommended by the American Academy of Neurology 4

For severe disease, intravenous immunoglobulin (IVIG) can be considered as an additional therapy, as suggested by the American College of Rheumatology 3
If there is any evidence of myocardial involvement, immune checkpoint inhibitor therapy should be permanently discontinued, according to the National Comprehensive Cancer Network 3

For grade 3-4 toxicity, therapy should be held and potentially resumed in consultation with rheumatology, as recommended by the American Society of Clinical Oncology 3

Cardiac involvement can be life-threatening and should not be overlooked, as warned by the American Heart Association 3, 4
Caution is advised when rechallenging patients with immune checkpoint inhibitors after myositis, as noted by the American College of Rheumatology 3