Are nerve conduction studies altered in functional neurological disorders?

Background

Functional neurological disorders represent conditions without a readily identifiable origin or laboratory-supported diagnostic. We report a case of functional neurological disorder, presenting with muscle weakness with alterations in F-waves on the affected side.

Case report

A retrospective case review of a patient seen in clinic. Electrophysiological evaluation included nerve conduction studies, including recording of F-waves in lower limbs, and needle EMG. A patchy sensory loss and unilateral muscle weakness of the left lower limb persisted nine days after a 40-year-old female patient developed bilateral lower limb weakness following a laparoscopic surgery. MRI was negative for radicular compression, myelopathy, or lumbosacral plexopathy. F-waves of the peroneal and tibial nerves on the left were absent or of reduced persistence and amplitude compared to the asymptomatic right side.

Significance

The observation of unilateral alterations of F-wave parameters could be interpreted as an asymmetrical decrease of alpha motor neuron excitability on L4 – S2 segments. In the absence of peripheral nervous system dysfunction or a structural lesion, the results here suggest a central control dysfunction or point to a more complex peripheral role. Further research is necessary to determine the frequency of these findings in a larger group of patients while incorporating other late responses, such as H (Hoffman) reflex, and measures of cortical excitability.