Reader response: Therapeutic benefits of early electrophysiological testing in a functional neurology case

We read the article by Powell et al.¹ with interest. We advocate using clinical neurophysiology to help make the diagnosis of functional neurologic disorders (FND). Such testing can improve diagnostic certainty. We agree that the testing is valuable but for the opposite reason that the authors suggest. The clinical findings themselves were suggestive of FND. The neurophysiology points to a cerebral abnormality of motor and sensory functions. Despite the normal neuroimaging, this still could have been an episode of demyelination or another disorder. Functional disorders are often seen together with other neurologic disorders,² a situation often referred to as functional overlay. These abnormal evoked responses could be the consequence of FND. However, many more clinical neurophysiologic studies of FND have shown normal central motor and sensory conductions.³ If the findings were normal, that would be good evidence for a functional disorder. As they were abnormal, the interpretation is less certain. From a clinical point of view, the patient had positive features of FND, so it was reasonable to treat those aspects of his presentation, but not—in our view—using the clinical neurophysiology as evidence of that diagnosis.

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