Motor Unit Number Index in Evaluating Patients With Lumbar Spinal Stenosis

Motor unit number index is a quantitative electrophysiological measure that provides an index of the number of motor neurons supplying a muscle. The aim of this exploratory study was to assess the utility of motor unit number index in the evaluation of patients with lumbar spinal stenosis.

Participants were assigned to three groups: clinical and radiological lumbar stenosis (lumbar spinal stenosis with neurogenic intermittent claudication), group A; radiological lumbar spinal stenosis without neurogenic intermittent claudication, group B; and a control group, group C. Patients self-rated their pain and functional disability using the numerical rating scale and a series of functional questionnaires. An electromyographer performed nerve conduction tests, electromyography, and motor unit number index testing.

Seventeen patients completed the study. There were 9, 5, and 3 patients in groups A, B, and C, respectively. There were no discernable differences in motor unit number index values of any individual muscle or combined motor unit number index score between the three groups. Motor unit number index values did not correlate to pain/functional measures.

In this exploratory study, motor unit number index did not demonstrate discriminatory ability between patients with lumbar spinal stenosis and was not correlated with pain and functional measures. Further study is needed to explore motor unit number index's role in longitudinal evaluation of patients with the clinical syndrome of lumbar spinal stenosis.