When Weakness Persists Beyond Its Apparent Cause: A Case Report of Myasthenia Gravis.

Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction characterised by fluctuating, fatigable skeletal muscle weakness. Its overlap with reversible causes of weakness such as hypokalemia can easily delay recognition. We report the case of a 40-year-old man who presented with one week of profuse diarrhea and vomiting, along with two days of generalized limb weakness. Investigations revealed hypokalemia and hypomagnesemia, and his limb weakness partially improved after fluid and electrolyte correction, which raised suspicion of an additional underlying cause contributing to the persistent weakness. He was noted to have bilateral ptosis, and further history uncovered three months of fatigable weakness that worsened towards the end of the day, with slurred nasal speech, difficulty chewing, and nasal regurgitation. Examination showed a positive curtain sign, bilateral ptosis that improved with ice pack test, and fatigable proximal limb weakness with preserved reflexes. Anti-acetylcholine receptor antibodies were strongly positive, and contrast-enhanced computed tomography (CT) scan of the chest revealed the presence of thymoma in the anterior mediastinum. He responded well to pyridostigmine and oral prednisone. Thymectomy was subsequently planned. This case is a reminder that weakness outlasting its apparent cause warrants a neurological evaluation, since a concurrent electrolyte disturbance can readily mask an underlying myasthenic process.