If a Pt has diplopia, dysphagia, dysphonia, or dysarthria, particularly if these complaints are intermittent, or if the Ex finds an unexplained ocular, facial, or bulbar palsy, such as ptosis, strabismus, or mild hypernasal speech, suspect myasthenia gravis. Myasthenics may have little or no deficit when rested, as when first arising in the morning, but as the day wears on, or as they use their CrN muscles to look, talk, swallow, or chew, the weakness gets worse. Symptoms are often worsened by a rise in body temperature and often improved by cold. This pathologic fatigability of muscles, particularly of CrN muscles, is virtually pathognomonic of myasthenia gravis. Myasthenic Pts have a deficit in cholinergic transmission at the motor end plates of skeletal muscles. The diagnosis depends on clinical demonstration of the pathologic fatigability, repetitive nerve stimulation that shows a decrementing response, restoration of strength by giving a cholinergic drug, and demonstration of antibodies that block acetylcholine receptors at motor end plates of the skeletal muscles or IgG antibodies against the muscle-specific kinase (MuSK) in cases of seronegative myasthenia gravis.
Electrical testing for myasthenia includes repetitive stimulation of a peripheral nerve while recording the amplitude of the action potentials generated in the muscle fibers. Myasthenics show a decrement in the amplitude of muscular contraction after repetitive electrical stimulation of the nerve. The repetitive nerve stimulation test (Jolly's test) provides entirely objective data. It eliminates the need for the Pt's active participation, as required by the repetitive exercise tests. Single muscle fiber analysis also aids in establishing the diagnosis.