An Elderly Woman With Ptosis, Areflexia, and Weakness

A 55-year-old nonsmoker African American woman presented with a 2-week history of severe bilateral arm and leg weakness, along with a 4-month history of ptosis and double vision ( Fig. 76-1 ). These symptoms were aggravated by activity. She also had constipation and dry mouth.

On examination, she showed severe bilateral ptosis and ophthalmoplegia ( Fig. 76-1 ). Pupils were equal and reactive to light. The patient showed generalized weakness, more proximal than distal, along with areflexia that did not improve on repetitive tapping. Sensory exam was unremarkable and an edrophonium test was positive.

What is the Differential Diagnosis?

This patient has many features that are suggestive of myasthenia gravis (MG), including ptosis and ophthalmoplegia with recent onset, and the positive response to the edrophonium. The dry mouth and constipation are somewhat unusual, but she could also have Sjögren syndrome. Botulism may present like this, but this patient did not have pupillary involvement.

Another possibility is that this patient has Lambert–Eaton myasthenic syndrome (LEMS), but prominent ptosis is unusual in this condition.

What do you do Next?

Lab analysis showed negative AChR, MuSK, and VGCC antibodies. CT of the chest showed no evidence of neoplasm or thymus enlargement.

The patient underwent repetitive stimulation test and nerve conduction studies showing: left ulnar amplitude—4.30 mV pre and 9.10 mV on tetanic contraction, right median amplitude—6.90 mV pre and 11.00 mV on tetanic contraction. Initial decremental response of 67.3% was observed in the right abductor digiti-quinti muscle at 3 Hz stimulation. Immediately after 15 seconds of tetanic contraction, there was a 106% incremental response ( Fig. 76-2 ). Nerve conduction studies were normal showing no evidence of peripheral neuropathy, and needle EMG showed no denervation and scattered small polyphasic motor unit action potentials with mild variability.