MED-24. Unusual presentation of myasthenia gravis with isolated neck muscle weakness.

Myasthenia gravis cases presenting with limited neck muscle weakness are uncommon. Patients initially present complaining of fatigable muscle weakness such as ptosis or diplopia. A 73-year-old man presented to the emergency department with a 3-day history of positional dysphagia and a drooping head. He denied diplopia, weakness of his face or extremities. Past medical history significant for unspecified arthritis, hypertension and myocardial infarction. Medications included prednisone, valsartan, and aspirin. Examination revealed normal cranial nerve function, without ptosis and 5/5 power with 2+ deep tendon reflexes in all 4 extremities. However, he had 3/5 weakness of neck flexion and extension. With repetition, neck weakness diminished to 2/5. There was no fatigability of muscle strength involving other muscle groups. Routine laboratory and TSH were within normal limits. ANA and HLA-B27 were also negative. An edrophonium test was positive with reversal of neck weakness to 5/5 power. CT thorax did not show evidence of a thymoma. Acetylcholine receptor antibody was positive at 45. He was placed on pyridostigmine and prednisone with significant improvement in his symptoms. Electromyography performed one month after initiating treatment revealed defect in the neuromuscular junction (NMJ) transmission. Generally patients with myasthenia gravis present to physicians complaining of specific muscle weakness and not of generalized fatigue. Localized weakness to single muscle groups does occur and most commonly affect eye muscles (ocular myasthenia). Isolated weakness due to myasthenia gravis has been reported involving the distal hand, unilateral ptosis or unilateral abducens nerve palsy. Although most cases of isolated neck weakness are due to myopathies, our case brings to light the rare possibility of myasthenia gravis as cause of isolated neck weakness.

A. Marte-Grau, MD, J. Akong, MD, J. Lantz, MD, and C. Scherer, MD. University of Virginia, Roanoke-Salem Program, Roanoke, VA.