Management of Acute Worsening Proximal Muscle Weakness Leading to Collapse

Immediate Assessment and Stabilization

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, 3
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
Assess for bulbar symptoms including dysphagia, dysarthria, and facial weakness which indicate impending respiratory compromise 1
Consider hospitalization for patients with severe weakness limiting mobility, respiratory involvement, or dysphagia 2, 3

Check CK and aldolase levels urgently - elevations suggest myositis or rhabdomyolysis requiring immediate intervention 2, 3
Obtain troponin and ECG to evaluate myocardial involvement, as cardiac manifestations can be life-threatening 2, 3
Urinalysis for myoglobinuria to assess for rhabdomyolysis 2, 3
Check inflammatory markers (ESR and CRP) 2, 3

Fluctuating, exercise-dependent weakness of proximal extremities or bulbar muscle groups is characteristic of myasthenia gravis crisis 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 for myasthenia gravis crisis 1
Obtain anti-AChR and antistriational antibodies for myasthenia gravis diagnosis 2, 3
Symmetric proximal muscle weakness developing over days to weeks is characteristic of inflammatory myositis 4, 5
CK elevation ≥3× upper limit of normal suggests inflammatory myositis 2, 3

Hold any immune checkpoint inhibitors permanently for grade 3-4 myositis (severe weakness limiting self-care) 2, 3
Initiate methylprednisolone 1-2 mg/kg IV daily or higher dose bolus for severe compromise in grade 3-4 myositis 2, 3
Urgent referral to rheumatology and/or neurology is recommended for grade 3-4 myositis 2, 3
Consider plasmapheresis for acute or severe disease, preferred over IVIG when rapid response is needed 2, 3
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, 3, 1
Critical: Do not perform plasmapheresis immediately after IVIG as it will remove the immunoglobulin 2, 3

Myositis-specific autoantibodies (anti-TIF1γ, anti-NXP2) especially if muscle symptoms preceded any immunotherapy should be tested 2, 3
ANA, RF, anti-CCP to evaluate differential diagnosis should be tested 2, 3
Consider paraneoplastic autoantibody testing 2, 3
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, 3, 4
MRI of affected muscle groups to identify extent of involvement and guide biopsy site 2, 3, 4
Consider muscle biopsy when diagnosis remains uncertain after initial workup 2, 3

Avoid the following medications that can worsen neuromuscular weakness: β-blockers, IV magnesium 1
Avoid fluoroquinolones, aminoglycosides, macrolides as they can worsen neuromuscular weakness 1
Avoid anticholinergic medications as they can worsen neuromuscular weakness 1
Hold statins immediately as they can contribute to myopathy 2, 3