Workup and Management for Progressive Left Arm Weakness
The comprehensive workup for progressive left arm weakness should include neurological consultation, MRI imaging of the brain and spine, laboratory testing, and electrophysiological studies to identify the underlying cause and guide appropriate management. 1, 2
Initial Diagnostic Workup
Neuroimaging
- MRI of the cervical spine with and without contrast - Essential first-line imaging to:
- MRI of the brain with and without contrast - To evaluate for:
Laboratory Testing
- Complete blood count
- Comprehensive metabolic panel
- Inflammatory markers (ESR, CRP)
- HbA1c, vitamin B12, folate, TSH
- Serum protein electrophoresis and immunofixation
- Autoimmune screening: ANA, ESR, CRP, ANCA, anti-smooth muscle, SSA/SSB, RNP, anti-dsDNA 1, 2
- Consider paraneoplastic antibody panel including ANNA-1 (anti-Hu) 1
Electrophysiological Studies
- EMG and nerve conduction studies to differentiate between:
Additional Testing Based on Clinical Suspicion
- Lumbar puncture with CSF analysis for:
- Serum antiganglioside antibody tests if Guillain-Barré syndrome is suspected 1
Management Algorithm Based on Etiology
1. If Immune-Mediated Neuropathy (e.g., Guillain-Barré Syndrome)
Grade 2 (moderate symptoms):
- Discontinue any immune checkpoint inhibitors if applicable
- Neurology consultation
- Consider IVIG (0.4 g/kg/day for 5 days) or plasmapheresis 1
Grade 3-4 (severe symptoms):
- Hospital admission with capability for ICU transfer
- Start IVIG (0.4 g/kg/day for 5 days) or plasmapheresis
- Consider methylprednisolone (2-4 mg/kg/day or pulse dosing at 1 g daily for 5 days)
- Frequent neurological checks and pulmonary function monitoring 1
2. If Myasthenia Gravis
Grade 2 (mild generalized weakness):
- Pyridostigmine starting at 30 mg PO three times daily, gradually increasing to maximum of 120 mg four times daily
- Prednisone 0.5-1 mg/kg/day orally 1
Grade 3-4 (moderate to severe weakness):
- Hospital admission with ICU-level monitoring if needed
- Continue steroids
- Initiate IVIG 2 g/kg IV over 5 days or plasmapheresis
- Frequent pulmonary function assessment
- Daily neurologic review 1
3. If Compressive Myelopathy
- Neurosurgical consultation
- Surgical intervention for:
4. If Motor Neuron Disease (e.g., ALS)
- Neurology consultation for confirmation of diagnosis
- Riluzole therapy
- Multidisciplinary care including physical therapy, occupational therapy, and speech therapy
- Consider genetic testing if family history is present 3
Important Considerations and Pitfalls
Don't limit evaluation to the symptomatic region only - Cervical spine pathology can present with isolated lower extremity symptoms without upper extremity involvement 4
Avoid attributing symptoms to pre-existing conditions - New or progressive weakness requires thorough investigation even in patients with known neuropathy or other neurological conditions 5
Consider immune checkpoint inhibitor-related adverse events in patients receiving cancer immunotherapy - These can cause myasthenia gravis, Guillain-Barré syndrome, or other neurological complications requiring prompt intervention 1
Distinguish true motor weakness from impaired spatial awareness - Parietal lobe dysfunction can mimic weakness but can be differentiated by having the patient indicate when both arms are level while eyes are closed 5
Monitor for respiratory involvement - Progressive weakness can affect respiratory muscles, requiring close monitoring of pulmonary function 1
Be aware that imaging findings may not always correlate with symptoms - Clinical examination remains essential in neurological diagnosis 2