What is the recommended treatment and management approach for a patient diagnosed with myositis?

Treatment and Management of Myositis

Treatment should be initiated with high-dose corticosteroids (prednisone 0.5-1 mg/kg/day for moderate disease, 1 mg/kg/day for severe disease) combined with early immunosuppressive therapy, with severity-based escalation including IV methylprednisolone, IVIG, and plasmapheresis for life-threatening cases. 1, 2

Initial Diagnostic Assessment

Before initiating treatment, establish disease severity through:

• Manual muscle testing of proximal muscle groups (hip flexors, shoulder abductors) bilaterally, assessing for true weakness versus pain-limited movement 2
• Creatine kinase (CK) levels as the primary marker—elevation ≥3× upper limit of normal indicates moderate-to-severe disease 1, 2
• Additional muscle enzymes: aldolase, AST/ALT, and LDH 2, 3
• Inflammatory markers: ESR and CRP 1, 2
• Myositis-specific autoantibodies (anti-TIF1γ, anti-NXP2, anti-HMGCR) for subtype classification 2, 4
• Cardiac evaluation with troponin, ECG, and consider cardiac MRI—myocardial involvement can be fatal if missed 2

Severity-Based Treatment Algorithm

Grade 1 (Mild): Minimal weakness, normal or mildly elevated CK

• Continue monitoring with NSAIDs or acetaminophen for pain 1
• Initiate prednisone 0.5 mg/kg/day if CK is elevated and weakness is documented 2
• Rheumatology consultation if symptoms persist beyond 2-4 weeks 2

Grade 2 (Moderate): Weakness limiting instrumental activities, CK ≥3× normal

• Initiate prednisone 0.5-1 mg/kg/day immediately 1, 2
• Add steroid-sparing agent early (within first 4-6 weeks): methotrexate, azathioprine, or mycophenolate mofetil to reduce long-term corticosteroid burden 1, 5
• Early rheumatology referral is mandatory for treatment coordination 1, 2
• Consider permanent discontinuation of immune checkpoint inhibitors if this is immune-related myositis with objective findings (abnormal EMG, MRI, or biopsy) 1

Grade 3-4 (Severe): Weakness limiting self-care, respiratory/cardiac involvement, dysphagia

• Hospitalize immediately for severe weakness or any cardiac/respiratory compromise 1
• Initiate prednisone 1 mg/kg/day orally OR methylprednisolone 1-2 mg/kg IV for severe compromise 1, 2
• Urgent rheumatology AND neurology referral within 24 hours 1
• Add IVIG therapy for severe disease, particularly with HMGCR antibodies or refractory weakness 1, 4
• Consider plasmapheresis for life-threatening weakness or when IVIG/steroids fail 1
• Permanently discontinue immune checkpoint inhibitors if any myocardial involvement is present 1

Critical Cardiac Monitoring

Screen for myocarditis in ALL myositis patients—this is the most dangerous pitfall as cardiac involvement can be rapidly fatal: 2

• Check troponin, BNP, and ECG at diagnosis 2
• Cardiology consultation for any abnormality or if troponin elevated 2
• Cardiac MRI or echocardiogram if clinical suspicion exists 2

Steroid-Sparing Immunosuppression

If no improvement or CK remains elevated after 4-6 weeks of corticosteroids: 1, 5

• First-line options: methotrexate, azathioprine, or mycophenolate mofetil 1, 5
• Rituximab may be effective in certain myositis-specific antibody subtypes (anti-synthetase, anti-SRP) but use caution given prolonged biologic duration 1, 5
• Avoid anti-TNF agents in immune checkpoint inhibitor-related myositis—mixed evidence and potential for paradoxical worsening 6

Adjunctive Management

• Initiate physical therapy early to prevent contractures and muscle atrophy, even during active disease 2, 5
• Screen for malignancy in dermatomyositis, particularly with anti-TIF1γ antibodies 7, 8
• Monitor for interstitial lung disease with pulmonary function tests and high-resolution CT, especially in anti-synthetase syndrome 7, 9

Common Pitfalls to Avoid

• Delaying treatment while awaiting muscle biopsy—start corticosteroids immediately if clinical suspicion is high and CK is significantly elevated 2, 7
• Missing cardiac involvement—always check cardiac biomarkers and ECG at presentation 2
• Monotherapy with corticosteroids alone—combine with steroid-sparing agents early to reduce cumulative steroid toxicity 1, 5
• Rechallenging with immune checkpoint inhibitors without specialist consultation—high risk of recurrent, potentially fatal myositis 1
• Confusing polymyalgia-like syndrome with true myositis—the former has pain/stiffness without true weakness or CK elevation and requires different management 1