Motor Unit Number Index in Evaluating Patients with Lumbar Spinal Stenosis.

Cai, Haibi; Kroll, Mitchell; Annaswamy, Thiru

OBJECTIVE Motor Unit Number Index (MUNIX) is a quantitative electrophysiological measure that provides an index of the number of motor neurons supplying a muscle. The aim of this exploratory study is to assess the utility of MUNIX in the evaluation of patients with lumbar spinal stenosis (LSS). DESIGN Participants were assigned to three groups: clinical and radiological lumbar stenosis (LSS with neurogenic intermittent claudication [NIC])-group A, radiological LSS without NIC-group B, and a control group - group C. Each patient self-rated their pain and functional disability using the numerical rating scale (NRS) and a series of functional questionnaires. An electromyographer performed nerve conduction tests, electromyography, and MUNIX testing. RESULTS 17 patients completed the study. There were 9, 5, and 3 patients in groups A, B & C respectively. There were no discernable differences in MUNIX values of any individual muscle or combined MUNIX score between the three groups. MUNIX values did not correlate to pain/functional measures. CONCLUSION In this exploratory study, MUNIX did not demonstrate discriminatory ability between patients with LSS and was not correlated with pain and functional measures. Further study is needed to explore MUNIX's role in longitudinal evaluation of patients with the clinical syndrome of LSS.