Decremental response of the nasalis and hypothenar muscles in myasthenia gravis.

Repetitive nerve stimulation (RNS) is a standard diagnostic procedure in myasthenia gravis (MG). Although RNS sensitivity is highest in weak muscles, RNS is easier to perform in distal muscles that are often not affected. Twenty-five patients with MG were assessed to compare the sensitivity of RNS of the nasalis muscle to that of the hypothenar muscles. Abnormal decrement was found in hypothenar muscles in 9 patients (36%) and in the nasalis muscle in 13 patients (52%). RNS of the nasalis muscle appeared more useful to detect abnormal neuromuscular transmission in patients with oculobulbar MG (5 of 5) than hypothenar RNS (1 of 5). In patients with generalized MG, hypothenar muscles had a similar yield of abnormal RNS tests.