Pearls: myasthenia

Abstract

Myasthenia gravis is typically an acquired autoimmune disorder in which antibodies are directed at structural components of the neuromuscular junction, most commonly the nicotinic acetylcholine receptor. The clinical manifestations of skeletal muscle weakness are broad. Patients most often report fatigable muscle weakness. The eyelid levators and extraocular muscles are most commonly affected, resulting in symptoms of ptosis and diplopia. Symptoms may be confined to the eyes (ocular myasthenia) or reflect bulbar, limb, or respiratory muscle weakness (generalized myasthenia). The diagnosis is based on a characteristic history and the finding of fatigable muscle weakness on examination, and may be supported by diagnostic tests such as finding elevated titers of acetylcholine receptor or muscle-specific receptor tyrosine kinase (MuSK) antibodies, a positive Tensilon test, a decremental response on slow repetitive nerve stimulation, and abnormal jitter on single fiber electromyography. This article presents a series of pearls to aid in the clinical and laboratory diagnosis of myasthenia gravis, emphasizing key historical features, common and characteristic findings on examination, and potential pitfalls in the use of ancillary diagnostic studies.