New neurophysiologic test holds promise for diagnosis of myasthenia gravis

The authors describe a new neurophysiologic test called repetitive ocular vestibular evoked myogenic potentials (RoVEMP) for diagnosing myasthenia gravis.

Study design

This prospective case-control study investigated whether the novel RoVEMP test distinguishes myasthenia from other neuromuscular diseases. The test, which measures neuromuscular transmission of extraocular muscles, was administered to 92 patients with myasthenia, 4 patients with Lambert-Eaton syndrome, 2 patients with congenital myasthenia, 33 neuromuscular controls and 22 healthy controls.

Outcomes

The mean decrement in RoVEMP was found to be significantly higher in patients with myasthenia than in either control group. Sensitivity of RoVEMP was 80% in ocular myasthenia and 63% in generalized myasthenia. Six out of 7 seronegative myasthenia patients with isolated ocular muscle weakness had positive RoVEMP.

The authors conclude that RoVEMP is able to measure neuromuscular transmission of extraocular muscles. This test has clear added value in supporting the diagnosis of myasthenia, particularly in diagnostically challenging patients with negative antibody tests and negative repetitive nerve stimulation testing.

Limitations

Study limitations include the small number of patients, relatively low sensitivity and specificity of RoVEMP and definitions used for labeling patients with seronegative myasthenia.

Clinical significance

Provided these results can be replicated in further studies, RoVEMP will be a useful addition to neurophysiologic testing to establish a diagnosis of myasthenia when serology for myasthenia is negative.