Utility of Repetitive Nerve Stimulation in the Diagnosis of Myasthenia Gravis in the Inpatient Setting.

Objectives: Sensitivity and specificity of Repetitive Nerve Stimulation (RNS) is typically reported from outpatient centers, and we hypothesized that these values might not apply to hospitalized patients with higher grades of weakness. RNS may be helpful in rapidly confirming diagnosis of myasthenia gravis (MG) in the inpatient setting, as results from confirmatory antibody testing are often delayed. We sought to characterize the sensitivity and specificity of RNS in the inpatient setting to assist in the early diagnosis of MG.

Methods: We performed a retrospective analysis of all adult patients who had inpatient RNS at our center from 2016 to 2021. Inclusion criteria included RNS performed at least at one site and a neurological evaluation which prompted an electrodiagnostic study to evaluate for neuromuscular junction (NMJ) pathology. Descriptive statistics and Fisher exact analysis were performed.

Results: Of the 32 identified hospitalized patients, 6 had greater than 10% decrement on slow RNS, confirming NMJ dysfunction. Five were diagnosed with MG, and 1 with Lambert-Eaton myasthenic syndrome. Of the 26 patients with normal RNS, 25 ultimately had alternative causes of weakness. One was later diagnosed as seronegative MG based on clinical improvement with acetylcholinesterase inhibitors. In our inpatient population, the overall sensitivity and specificity of RNS were 83.3% and 96.2% respectively. There was a statistically significant association between a positive RNS and diagnosis of MG (P = .0002).

Conclusions: RNS is a highly sensitive and specific test for the diagnosis of MG in an inpatient setting, and these results are likely more rapidly available compared to antibody testing.