What is the appropriate next step in management for a patient with new right‑arm weakness who has not improved with muscle‑relaxant and steroid therapy?

Urgent Neurological Workup Required

The appropriate next step is immediate neurological consultation with comprehensive electrodiagnostic testing (EMG/NCS) and laboratory evaluation including CK, aldolase, inflammatory markers, and autoantibodies, as unilateral arm weakness unresponsive to muscle relaxants and steroids suggests a serious neuromuscular disorder requiring urgent diagnosis. 1, 2

Critical Red Flags Assessment

The failure to improve with empiric muscle relaxants and steroids is a major red flag that demands immediate escalation of care. 1, 2 You must urgently assess for:

• Respiratory compromise: Measure negative inspiratory force (NIF) and vital capacity immediately, as neuromuscular disorders can progress to respiratory failure rapidly 1, 2
• Bulbar symptoms: Evaluate for dysphagia, dysarthria, or facial weakness, which signal impending respiratory compromise 1, 2
• Pattern of weakness: Determine if this is truly isolated to one arm or if there is subtle bilateral, ascending, or proximal involvement that suggests systemic disease 1

Mandatory Diagnostic Workup

Immediate Laboratory Studies

• Muscle inflammation markers: CK, aldolase, AST, ALT, and LDH to evaluate for myositis 3, 4
• Cardiac evaluation: Troponin and ECG to assess for myocardial involvement, which would dramatically change management 3, 4
• Inflammatory markers: ESR and CRP 3, 4
• Autoantibody panel: Anti-AChR and anti-striational antibodies for myasthenia gravis 3
• Urinalysis: To assess for rhabdomyolysis/myoglobinuria 3, 4

Neurological Testing

• Electrodiagnostic studies: EMG with repetitive nerve stimulation and nerve conduction studies to differentiate between myopathy, neuropathy, and neuromuscular junction disorders 3, 1
• MRI of spine: With or without contrast to rule out compressive lesions, nerve root enhancement, or cord pathology 3, 1
• Consider lumbar puncture: If Guillain-Barré syndrome or inflammatory process suspected, looking for elevated protein and cell count 3, 1

Differential Diagnosis Algorithm

If Weakness is Proximal with Elevated CK

This suggests myositis. 3, 1 Initiate prednisone 0.5-1 mg/kg/day (typically 60-80 mg daily) and refer urgently to rheumatology. 3, 2 Consider concurrent steroid-sparing agents such as methotrexate or azathioprine, which take 3-6 months to reach full efficacy. 2

If Weakness is Fluctuating with Normal Sensation

This suggests myasthenia gravis. 3, 1 Start pyridostigmine 30 mg orally three times daily, gradually increasing to maximum 120 mg four times daily. 3 Initiate prednisone 1-1.5 mg/kg daily if symptoms are moderate to severe. 3 Avoid beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides. 3

If Weakness has Sensory Changes or Areflexia

This suggests peripheral neuropathy or Guillain-Barré syndrome. 3, 1 Admit to hospital with ICU capability and initiate IVIG (0.4 g/kg/day for 5 days) or plasmapheresis. 3, 1, 2 Monitor respiratory function closely with serial NIF and vital capacity measurements. 3, 1, 2

If Weakness is Isolated Without Clear Systemic Features

Consider focal nerve entrapment, radiculopathy, or central lesion. 1 MRI of cervical spine and brain may be needed to rule out structural causes. 1

Mandatory Specialist Consultation

Neurologist involvement is mandatory for all grades of unexplained weakness, given the potential for rapid deterioration. 2 Do not delay consultation while awaiting test results. 2

Additional specialists to consider:

• Rheumatology: If inflammatory myopathy suspected 3, 2
• Pulmonology: If any respiratory symptoms present 2
• Physical therapy: For rehabilitation once diagnosis established 2

Critical Pitfalls to Avoid

• Do not assume this is a simple musculoskeletal problem just because it involves one limb—unilateral presentation can be the initial manifestation of systemic neuromuscular disease 1
• Do not continue empiric steroids without a diagnosis, as this can mask serious conditions and delay appropriate treatment 4
• Do not discharge without neurology evaluation if any concern for progressive weakness, as conditions like myasthenia gravis and Guillain-Barré can deteriorate rapidly 3, 1, 2
• Always evaluate for cardiac involvement by checking troponin and ECG, as myocardial involvement requires more aggressive immunosuppression 3, 4

Medication Review

Review all current medications for agents that may worsen neuromuscular function, particularly statins (which can cause myopathy), and consider holding them during the diagnostic workup. 3, 2