What is the initial treatment for myositis?

Initial Treatment for Myositis

Start high-dose corticosteroids immediately at 1 mg/kg/day of prednisone (or equivalent) for all patients with confirmed myositis, and strongly consider adding a steroid-sparing agent like methotrexate from the outset to better control disease activity and reduce corticosteroid-related toxicity. 1

Critical First Steps: Rule Out Life-Threatening Complications

Before initiating treatment, you must immediately assess for cardiac involvement and myasthenia gravis, as these dramatically alter prognosis and management:

• Check troponin and obtain ECG immediately in every myositis patient, as myocarditis occurs in up to 20% of cases and carries a mortality rate of approximately 20% (compared to <10% in idiopathic inflammatory myositis without cardiac involvement). 1, 2
• Screen for myasthenia gravis with anti-AChR and antistriational antibodies, as 12.5% of myositis patients have concurrent myasthenia gravis requiring different management. 1
• Perform urinalysis to detect myoglobinuria and assess for rhabdomyolysis, which is life-threatening. 1, 2
• If any cardiac symptoms, elevated troponin, or ECG abnormalities are present, obtain cardiac MRI and consider hospitalization with IV methylprednisolone 1-2 mg/kg/day instead of oral therapy. 1, 2

Severity-Based Treatment Algorithm

Grade 1 (Mild Weakness)

• Continue with oral prednisone 0.5 mg/kg/day if CK is elevated and muscle weakness is present (not just pain). 1
• Acetaminophen or NSAIDs for myalgia if no contraindications exist. 1
• Hold statins if the patient is taking them. 1

Grade 2 (Moderate Weakness Limiting Instrumental Activities)

• Initiate prednisone 0.5-1 mg/kg/day if CK is ≥3× upper limit of normal. 1
• Refer urgently to rheumatology or neurology for co-management. 1
• Consider permanent discontinuation of any causative agents (like checkpoint inhibitors) if objective findings are present on EMG, MRI, or biopsy. 1
• Monitor CK levels closely—continue the initial high dose until CK normalizes, as tapering while CK remains elevated frequently causes relapse. 3

Grade 3-4 (Severe Weakness Limiting Self-Care)

• Hospitalize immediately for severe weakness, dysphagia, respiratory compromise, or cardiac involvement. 1, 2
• Start prednisone 1 mg/kg/day orally or methylprednisolone 1-2 mg/kg/day IV for severe compromise (respiratory failure, dysphagia, severe mobility limitation). 1, 2
• Add IVIG therapy (1-2 g/kg divided over 2 consecutive days) for patients with inadequate response to corticosteroids within 2-4 weeks. 1, 4, 2
• Consider plasmapheresis as it has faster onset than IVIG for refractory or life-threatening cases. 1, 2
• Permanently discontinue any causative checkpoint inhibitors if myocardial involvement is present. 1

Essential Monitoring and Corticosteroid Tapering Strategy

The relationship between CK levels and treatment success is critical:

• Do not taper corticosteroids until CK normalizes—achieving low-normal CK range predicts prolonged remission, while tapering with elevated CK leads to biochemical and clinical relapse. 3
• Taper slowly over 4-6 weeks once CK normalizes and clinical improvement occurs. 1, 3
• A rise in CK even within the normal range signals impending relapse and warrants holding the taper. 3

Second-Line and Steroid-Sparing Agents

If symptoms and CK do not improve after 4-6 weeks of high-dose corticosteroids, or if unable to taper below 10 mg/day prednisone:

• Add methotrexate as the preferred steroid-sparing agent (therapeutic effect observed within 8 weeks). 1, 5
• Alternative options include azathioprine or mycophenolate mofetil. 1, 5
• For refractory cases, rituximab shows evidence of benefit, particularly in patients with certain myositis-specific autoantibodies. 1, 6, 5
• Avoid TNF-α antagonists as they can exacerbate interstitial lung disease and increase infection risk in myositis patients. 5
• Consider abatacept or alemtuzumab as rescue therapy for glucocorticoid-refractory myocarditis, though evidence is limited. 1

Critical Pitfalls to Avoid

• Do not assume all CK elevations require corticosteroids—exercise-induced muscle damage can produce CK >10,000 U/L without requiring treatment; confirm true muscle weakness (not just pain) before initiating immunosuppression. 1, 2
• Never administer IVIG immediately before plasmapheresis as it will be removed. 4
• Do not use IL-6 inhibitors (tocilizumab) in patients with concurrent colitis or GI metastases due to intestinal perforation risk. 1
• Always check IgA levels before IVIG to prevent severe anaphylactic reactions in IgA-deficient patients. 4
• If a patient fails to respond to standard therapy, repeat muscle biopsy to exclude other myopathies before escalating immunosuppression. 5

Adjunctive Therapy

Combine pharmacological treatment with individualized, supervised exercise programs from the early phase of disease, as this combination improves muscle performance and reduces disease activity. 6