A prospective multicentre study on sural nerve action potentials in ALS.

Objective: To evaluate sensory nerve conduction studies in ALS in a prospective multicentre study involving 7 neurophysiologists from 6 European countries.

Methods: Bilateral sural potentials were obtained in 35 ALS patients and 35 age-matched controls according to a standardised examination protocol using antidromic surface technique. The recordings from the right sural nerve of the controls were used for reference values. A reduction from the mean of controls greater than 2 SDs was considered abnormal.

Results: Reduced sensory nerve action potential (SNAP) amplitude or reduced conduction velocity (CV), or both, was found in 6 ALS patients (17%). Decrease in CV was the most frequent finding, and was observed in 8 nerves from 5 patients. Reduced SNAP amplitude was found in 2 nerves from 2 patients. All changes were minor ranging from -2.1 to -3.2 SDs.

Conclusions: This is the first standardised multicentre study on sensory potentials in ALS. It confirms that although normal sensory findings should be expected in the majority of ALS patients, minor abnormalities are not uncommon.

Significance: Mild sensory abnormalities do not necessarily exclude a diagnosis of ALS.