Myasthenia Gravis: The Daily PANCE Blueprint
A 32-year-old woman reports several months of fluctuating weakness that is mild in the morning but worsens as the day goes on. She has intermittent drooping of both eyelids, double vision, and by evening her voice becomes nasal and she has trouble chewing. Her symptoms improve with rest. On exam she has fatigable ptosis, with normal reflexes and normal sensation. Which of the following is the most appropriate initial test to confirm the diagnosis?
A. Serum acetylcholine receptor (AChR) antibodies
B. Edrophonium (Tensilon) test
C. Muscle biopsy
D. Serum creatine kinase
E. Nerve conduction velocity study
Answer and topic summary
The answer is A. Serum acetylcholine receptor (AChR) antibodies
Fatigable weakness that worsens with use and improves with rest — ptosis, diplopia, nasal speech, trouble chewing — is classic myasthenia gravis, an autoimmune attack on the acetylcholine receptors at the neuromuscular junction. The most appropriate and specific confirmatory test is serum AChR antibodies (positive in roughly 85% of generalized MG). The trap is the edrophonium (Tensilon) test: historically famous but now rarely used because of false results and cardiac risk. Muscle biopsy and creatine kinase point to muscle disease rather than the junction, and while repetitive nerve stimulation and single-fiber EMG support the diagnosis, antibody testing is the initial confirmatory study. Once confirmed, image the chest to look for a thymoma.
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