A 50-year-old male presented with complains of ptosis, difficulty in chewing and occasional difficulty in swallowing. There is no history of diplopia or visual loss. On examination, there is symmetric ptosis and mild restriction of extraocular muscle movement with finger abduction test 60deg. Nerve conduction study shows decremental response in orbicularis only. ERG revealed a myopathic pattern. Anti-AchR radioimmunoassay was negative. The most probable diagnosis would be:

Explanation

Ans. b. Generalized myasthenia gravis (Ref Harrison 19/e p2701, 18/e p3480-3482; Meritt's Neurology 12/e p389)Myasthenia gravis is a major cause of ptosis and diptopia. The distribution of muscle weakness has a characteristic pattem.The cranial muscles paicularly the lids and extraocular muscles are often involved early in the course, diplopia and ptosis are common initial complaints.