What is the appropriate management for a patient presenting with acute worsening proximal muscle weakness leading to collapse?

Management of Acute Worsening Proximal Muscle Weakness Leading to Collapse

For a patient presenting with acute worsening proximal muscle weakness severe enough to cause collapse, immediately assess for respiratory compromise by measuring negative inspiratory force and vital capacity, obtain urgent CK and troponin levels, and consider myasthenia gravis crisis requiring IVIG or plasmapheresis alongside high-dose corticosteroids if inflammatory myositis is suspected. 1, 2

Immediate Assessment and Stabilization

Respiratory Function Evaluation

• Measure negative inspiratory force and vital capacity immediately as respiratory failure is the most critical complication and may develop insidiously before sudden decompensation occurs 1, 3
• Assess for bulbar symptoms including dysphagia, dysarthria, and facial weakness which indicate impending respiratory compromise 1
• Arterial blood gas findings of severe hypoxemia and hypercapnia may not be apparent until respiratory failure is profound, so do not rely solely on clinical appearance 3
• Consider hospitalization for patients with severe weakness limiting mobility, respiratory involvement, or dysphagia 2

Critical Laboratory Workup

• Check CK and aldolase levels urgently - elevations suggest myositis or rhabdomyolysis requiring immediate intervention 2, 4
• Obtain troponin and ECG to evaluate myocardial involvement, as cardiac manifestations can be life-threatening 2
• Urinalysis for myoglobinuria to assess for rhabdomyolysis 2
• Check inflammatory markers (ESR and CRP) 2

Pattern Recognition for Diagnosis

Myasthenia Gravis Crisis Pattern:

• Fluctuating, exercise-dependent weakness of proximal extremities or bulbar muscle groups 1
• Administer IV pyridostigmine immediately (1 mg IV = 30 mg oral) or IM neostigmine (0.75 mg IM = 30 mg oral) if IV access unavailable 1
• Obtain anti-AChR and antistriational antibodies 2

Inflammatory Myositis Pattern:

• Symmetric proximal muscle weakness developing over days to weeks 2
• CK elevation ≥3× upper limit of normal 2
• Muscle weakness is more typical than pain 2

Grade-Based Management Algorithm

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

• Hold any immune checkpoint inhibitors permanently 2
• Initiate methylprednisolone 1-2 mg/kg IV daily or higher dose bolus for severe compromise 2
• Urgent referral to rheumatology and/or neurology 2
• Consider plasmapheresis for acute or severe disease - this is preferred over IVIG when rapid response is needed 2
• If using IVIG, administer 2 g/kg IV over 5 days (0.4 g/kg/day), but note that onset of action is slower than plasmapheresis 2, 1
• Critical: Do not perform plasmapheresis immediately after IVIG as it will remove the immunoglobulin 2

Escalation for Non-Response

• If symptoms worsen or no improvement after 2 weeks, consider biologics including rituximab, TNF-α antagonists, or IL-6 antagonists 2
• If symptoms and CK levels do not resolve after 4 weeks, add synthetic immunosuppressants such as methotrexate, azathioprine, or mycophenolate mofetil 2

Additional Diagnostic Considerations

Autoimmune Testing Panel

• Myositis-specific autoantibodies (anti-TIF1γ, anti-NXP2) especially if muscle symptoms preceded any immunotherapy 2
• ANA, RF, anti-CCP to evaluate differential diagnosis 2
• Consider paraneoplastic autoantibody testing 2

Imaging and Neurophysiology

• EMG when diagnosis is uncertain or overlap with myasthenia gravis suspected - look for polyphasic motor unit action potentials of short duration and low amplitude with increased insertional activity 2
• MRI of affected muscle groups to identify extent of involvement and guide biopsy site 2
• Consider muscle biopsy when diagnosis remains uncertain after initial workup 2

Critical Medication Precautions

Avoid the following medications that can worsen neuromuscular weakness:

• β-blockers, IV magnesium 1
• Fluoroquinolones, aminoglycosides, macrolides 1
• Anticholinergic medications 1
• Hold statins immediately as they can contribute to myopathy 2

Common Pitfalls to Avoid

• Do not delay treatment waiting for definitive biopsy results when clinical presentation and CK elevation strongly suggest inflammatory myositis 5
• Do not assume normal arterial blood gases exclude respiratory compromise - neuromuscular respiratory failure can be subtle until sudden decompensation 3
• With elevated transaminases, consider differential diagnosis with immune-mediated hepatitis rather than assuming pure myositis 2
• Poor response to appropriate treatment is unusual when diagnosis is correct and should prompt reconsideration of alternative diagnoses 5

Infectious Myositis Consideration

If patient has fever, recent infection, or diabetes, consider bacterial myositis (70% Staphylococcus aureus):

• Obtain blood and urine cultures 6
• MRI may show multiple foci of nodular and ring enhancement in proximal muscle groups 6
• Initiate broad-spectrum antibiotics empirically while awaiting cultures 6
• Multifocal abscesses suggest transient bacteremia and require prolonged antibiotic therapy 6