Test Accurately Diagnoses Myasthenia Gravis

A test for ocular vestibular evoked myogenic potentials (oVEMP) has a sensitivity of 89% and a specificity of 64% for detecting myasthenia gravis, according to a case–control study of 55 adults published online ahead of print January 20 in Neurology.

"The presence of an oVEMP decrement is a sensitive and specific marker for myasthenia gravis," said Yulia Valko, MD, a resident at University Hospital Zurich in Switzerland, and her associates. "This test allows direct and noninvasive examination of extraocular muscle activity, with similarly good diagnostic accuracy in ocular and generalized myasthenia gravis."

Myasthenia gravis usually manifests first in the eyes, and early diagnosis and treatment can limit generalization. Nearly half of patients remain undiagnosed a year after onset, however, partly because standard tests often fail to detect isolated ocular myasthenia gravis, the researchers noted. The recently developed oVEMP test directly measures the activity of the extraocular inferior oblique muscle in response to repeated bursts of vibratory stimulation to the forehead. A decreased response, or decrement, indicates failed neuromuscular transmission, as with standard repetitive nerve stimulation. The researchers evaluated the test in 13 patients with isolated ocular myasthenia gravis, 14 patients with generalized myasthenia gravis, and 28 healthy controls. They defined the oVEMP decrement as the decrease between the second stimulus and the average of the fifth through ninth stimuli.

A repetition rate of 20 Hz best differentiated between cases (average decrement, -21.5%) and controls (average decrement, -2.8%), the researchers reported. When at least one eye showed a decrement, the ideal cutoff was a decrement of at least 15.2%, which detected myasthenia gravis with a sensitivity of 89% and a specificity of 64%. When both eyes were affected, the ideal cutoff for the smaller of the two decrements was at least 20.4%, which yielded a sensitivity of 100% and a specificity of 63%. For both cutoffs, the test was similarly sensitive for detecting ocular and generalized myasthenia gravis. For the unilateral cutoff, the sensitivity was 92% for patients with isolated ocular myasthenia gravis and 86% for patients with generalized myasthenia gravis. For the bilateral cutoff, specificity was 62% in ocular myasthenia gravis and 64% in generalized myasthenia gravis.

The results provide class III evidence that oVEMP can distinguish between patients with myasthenia gravis and healthy controls, "but future studies will need to confirm its diagnostic utility in clinical practice, where the main challenge is differentiation from patients with other neuro-ophthalmologic conditions," the researchers said. "The possibility to apply fast repetition rates is one important advantage of oVEMP, which is not possible by measuring voluntary saccadic eye movements. As a consequence, oVEMP allowed us to unmask myasthenic decrements even in clinically asymptomatic eyes."

Because the study used a confirmed diagnosis of myasthenia gravis as a benchmark, all patients were already being treated with cholinesterase inhibitors. Although participants underwent oVEMP testing in the morning before their first dose of medication, the test needs further study in drug-naïve patients, as well as in patients with worse limitations in their upward gaze, the researchers added.

—Amy Karon

A test for ocular vestibular evoked myogenic potentials (oVEMP) has a sensitivity of 89% and a specificity of 64% for detecting myasthenia gravis, according to a case–control study of 55 adults published online ahead of print January 20 in Neurology.

"The presence of an oVEMP decrement is a sensitive and specific marker for myasthenia gravis," said Yulia Valko, MD, a resident at University Hospital Zurich in Switzerland, and her associates. "This test allows direct and noninvasive examination of extraocular muscle activity, with similarly good diagnostic accuracy in ocular and generalized myasthenia gravis."

Myasthenia gravis usually manifests first in the eyes, and early diagnosis and treatment can limit generalization. Nearly half of patients remain undiagnosed a year after onset, however, partly because standard tests often fail to detect isolated ocular myasthenia gravis, the researchers noted. The recently developed oVEMP test directly measures the activity of the extraocular inferior oblique muscle in response to repeated bursts of vibratory stimulation to the forehead. A decreased response, or decrement, indicates failed neuromuscular transmission, as with standard repetitive nerve stimulation. The researchers evaluated the test in 13 patients with isolated ocular myasthenia gravis, 14 patients with generalized myasthenia gravis, and 28 healthy controls. They defined the oVEMP decrement as the decrease between the second stimulus and the average of the fifth through ninth stimuli.

A repetition rate of 20 Hz best differentiated between cases (average decrement, -21.5%) and controls (average decrement, -2.8%), the researchers reported. When at least one eye showed a decrement, the ideal cutoff was a decrement of at least 15.2%, which detected myasthenia gravis with a sensitivity of 89% and a specificity of 64%. When both eyes were affected, the ideal cutoff for the smaller of the two decrements was at least 20.4%, which yielded a sensitivity of 100% and a specificity of 63%. For both cutoffs, the test was similarly sensitive for detecting ocular and generalized myasthenia gravis. For the unilateral cutoff, the sensitivity was 92% for patients with isolated ocular myasthenia gravis and 86% for patients with generalized myasthenia gravis. For the bilateral cutoff, specificity was 62% in ocular myasthenia gravis and 64% in generalized myasthenia gravis.

The results provide class III evidence that oVEMP can distinguish between patients with myasthenia gravis and healthy controls, "but future studies will need to confirm its diagnostic utility in clinical practice, where the main challenge is differentiation from patients with other neuro-ophthalmologic conditions," the researchers said. "The possibility to apply fast repetition rates is one important advantage of oVEMP, which is not possible by measuring voluntary saccadic eye movements. As a consequence, oVEMP allowed us to unmask myasthenic decrements even in clinically asymptomatic eyes."

Because the study used a confirmed diagnosis of myasthenia gravis as a benchmark, all patients were already being treated with cholinesterase inhibitors. Although participants underwent oVEMP testing in the morning before their first dose of medication, the test needs further study in drug-naïve patients, as well as in patients with worse limitations in their upward gaze, the researchers added.

—Amy Karon

A test for ocular vestibular evoked myogenic potentials (oVEMP) has a sensitivity of 89% and a specificity of 64% for detecting myasthenia gravis, according to a case–control study of 55 adults published online ahead of print January 20 in Neurology.

"The presence of an oVEMP decrement is a sensitive and specific marker for myasthenia gravis," said Yulia Valko, MD, a resident at University Hospital Zurich in Switzerland, and her associates. "This test allows direct and noninvasive examination of extraocular muscle activity, with similarly good diagnostic accuracy in ocular and generalized myasthenia gravis."

Myasthenia gravis usually manifests first in the eyes, and early diagnosis and treatment can limit generalization. Nearly half of patients remain undiagnosed a year after onset, however, partly because standard tests often fail to detect isolated ocular myasthenia gravis, the researchers noted. The recently developed oVEMP test directly measures the activity of the extraocular inferior oblique muscle in response to repeated bursts of vibratory stimulation to the forehead. A decreased response, or decrement, indicates failed neuromuscular transmission, as with standard repetitive nerve stimulation. The researchers evaluated the test in 13 patients with isolated ocular myasthenia gravis, 14 patients with generalized myasthenia gravis, and 28 healthy controls. They defined the oVEMP decrement as the decrease between the second stimulus and the average of the fifth through ninth stimuli.

A repetition rate of 20 Hz best differentiated between cases (average decrement, -21.5%) and controls (average decrement, -2.8%), the researchers reported. When at least one eye showed a decrement, the ideal cutoff was a decrement of at least 15.2%, which detected myasthenia gravis with a sensitivity of 89% and a specificity of 64%. When both eyes were affected, the ideal cutoff for the smaller of the two decrements was at least 20.4%, which yielded a sensitivity of 100% and a specificity of 63%. For both cutoffs, the test was similarly sensitive for detecting ocular and generalized myasthenia gravis. For the unilateral cutoff, the sensitivity was 92% for patients with isolated ocular myasthenia gravis and 86% for patients with generalized myasthenia gravis. For the bilateral cutoff, specificity was 62% in ocular myasthenia gravis and 64% in generalized myasthenia gravis.

The results provide class III evidence that oVEMP can distinguish between patients with myasthenia gravis and healthy controls, "but future studies will need to confirm its diagnostic utility in clinical practice, where the main challenge is differentiation from patients with other neuro-ophthalmologic conditions," the researchers said. "The possibility to apply fast repetition rates is one important advantage of oVEMP, which is not possible by measuring voluntary saccadic eye movements. As a consequence, oVEMP allowed us to unmask myasthenic decrements even in clinically asymptomatic eyes."

Because the study used a confirmed diagnosis of myasthenia gravis as a benchmark, all patients were already being treated with cholinesterase inhibitors. Although participants underwent oVEMP testing in the morning before their first dose of medication, the test needs further study in drug-naïve patients, as well as in patients with worse limitations in their upward gaze, the researchers added.

—Amy Karon