The diagnostic and prognostic utility of repetitive nerve stimulation in patients with myasthenia gravis

Repetitive nerve stimulation (RNS) is a standard test for the diagnosis of myasthenia gravis (MG), where decrement of compound muscle action potentials (CMAP) corresponds to clinical muscle fatigability. Our aim was to ascertain the diagnostic and prognostic utility of RNS in MG patients. This study included MG patients treated between 01/2000 and 12/2016, with an observational period of at least one year and a minimum of two neurological examinations. Clinical and electrophysiological data were retrospectively gathered from patient records, and CMAP decrement was correlated with autoantibody titers and clinical disease severity at different time points. Ninety-four patients were included, with 88.3% of the cohort testing positive for acetylcholine receptor autoantibodies (AChR-Abs). RNS sensitivity was higher in patients with generalized disease (71.6%) than in purely ocular MG (38.5%). CMAP decrement did not significantly correlate with AChR-Ab titers, nor with clinical symptom severity at the time of testing or last follow up. However, there was a significant correlation between CMAP decrement and the worst recorded clinical status on a group level. RNS testing is more sensitive in generalized disease and AChR-Ab positive patients, but our data do not support RNS as a tool for long-term outcome prediction. Future studies with a prospective study design could help to overcome a number of limiting factors discussed in our study.