Neuroscience · Year 2 · from Neuroscience
Case 1: Myasthenia Gravis - Neuromuscular Junction Disorder
Patient Presentation
Demographics: 32-year-old female
Chief Complaint: Progressive double vision and difficulty swallowing over 3 weeks
History of Present Illness: A 32-year-old woman presents with intermittent double vision that worsens in the evening and after reading for extended periods. She has also noticed difficulty swallowing solid foods and occasional choking on liquids. Over the past week, she has developed drooping of her eyelids, particularly at the end of the day. She reports that symptoms improve after rest. She has also noticed her voice becoming more nasal-sounding by dinnertime. She denies weakness in her limbs, numbness, or sensory changes.
Physical Examination:
- Vital signs: BP 118/72, HR 78, RR 14, T 36.9C
- General: Appears comfortable at rest
- Neurological:
- Mental status: Alert, oriented, normal cognition
- Cranial nerves: Bilateral ptosis worse on sustained upgaze (fatigable ptosis); diplopia on lateral gaze; nasal voice quality; weak palate elevation bilaterally; facial weakness with flattened nasolabial folds
- Motor: Normal strength proximally and distally at rest; mild proximal weakness after repeated testing
- Sensory: Intact throughout
- Reflexes: 2+ and symmetric; no pathological reflexes
Workup:
- Acetylcholine receptor (AChR) antibodies: Positive (elevated at 15.2 nmol/L; normal <0.4)
- CT chest: 2.5 cm anterior mediastinal mass consistent with thymoma
- Repetitive nerve stimulation: Decremental response (>10% decrement at 3 Hz stimulation) in facial muscles
- Edrophonium (Tensilon) test: Transient improvement in ptosis and diplopia following administration
Diagnosis: Myasthenia gravis with thymoma
Treatment:
- Pyridostigmine 60 mg three times daily (acetylcholinesterase inhibitor)
- Prednisone 60 mg daily initiated with slow taper
- Referral to cardiothoracic surgery for thymectomy
- Pre-operative plasmapheresis to reduce antibody burden
- Education regarding myasthenic crisis precautions
Clinical Pearl: Myasthenia gravis exemplifies the critical importance of acetylcholine (ACh) in neuromuscular transmission. Autoantibodies against nicotinic acetylcholine receptors at the neuromuscular junction reduce the number of functional receptors, causing fatigable weakness. The characteristic fatigability reflects progressive depletion of ACh quanta with repeated stimulation when fewer receptors are available. Treatment with acetylcholinesterase inhibitors prolongs ACh action at the synapse, partially compensating for receptor loss.