Spinal Cord Stimulation Reduces Mechanical Hyperalgesia and Restores Physical Activity Levels in Animals with Noninflammatory Muscle Pain in a Frequency-Dependent Manner

Gong, Weiyi MD, PhD*†; Johanek, Lisa M. PhD; Sluka, Kathleen A. PhD, PT

Anesthesia & Analgesia:
doi: 10.1213/ANE.0000000000000239
Pain and Analgesic Mechanisms: Research Report
Abstract

BACKGROUND: Spinal cord stimulation (SCS) is an effective treatment for neuropathic pain, but its effect on chronic muscle pain is unclear. We designed this study to test the effect of SCS in an animal model of noninflammatory muscle pain.

METHODS: Male Sprague-Dawley rats were implanted with an epidural SCS lead on the upper lumbar spinal cord (L3-L4) under isoflurane anesthesia (4%). Ten days after implantation, chronic muscle pain was induced by giving 2 injections of pH 4 saline into the left gastrocnemius muscle, 5 days apart. In experiment 1, SCS was delivered daily (6-hour duration/day) for 4 days at one of 4 different frequencies (0 (sham), 4, 60, and 100 Hz) from day 6 to day 9. Paw withdrawal threshold and muscle withdrawal threshold were measured before the first injection, and before and during SCS daily. Physical activity (distance, crossing, stand, and grooming) was assessed before the first injection, before SCS on day 6 and during SCS on day 9. In experiment 2, SCS was delivered (6 hours) on day 6 at either 60 or 100 Hz. Paw withdrawal threshold and muscle withdrawal threshold were assessed before the first injection, before and during SCS on day 6, and daily for the following 3 days (day 7–day 9).

RESULTS: Paw withdrawal threshold and muscle withdrawal threshold significantly decreased bilaterally after the second injection of acidic saline. SCS delivered at 60 or 100 Hz significantly reversed the decreased paw withdrawal threshold and muscle withdrawal threshold bilaterally when compared with that of sham SCS, but 4 Hz SCS had no effect on paw withdrawal threshold and muscle withdrawal threshold. SCS (60 or 100 Hz) delivered daily provided a persistently reversed effect, and SCS delivered singly provided a carryover effect for 24 hours. During 60 Hz SCS, the distance traveled and the number of crossings increased significantly when compared with that of sham SCS.

CONCLUSIONS: The current study shows that higher frequencies of SCS (60 and 100 Hz) significantly reduce mechanical hyperalgesia of the paw and muscle in an animal model of noninflammatory muscle pain, and 60 Hz SCS restores physical activity levels of animals, not 4 Hz.

In Brief

Published ahead of print May 5, 2014

Author Information

From the *Department of Anesthesiology, Fujian Medical University Union Hospital, Fuzhou City, Fujian, China; Department of Physical Therapy and Rehabilitation Science, University of Iowa, Carver College of Medicine, Iowa City, Iowa; and Medtronic Neuromodulation, Medtronic, Inc., Minneapolis, Minnesota.

Accepted for publication January 15, 2014.

Published ahead of print May 5, 2014

Funding: Funded by Medtronic, Inc.

Conflicts of Interest: See Disclosures at the end of the article..

Reprints will not be available from the authors.

Address correspondence to Kathleen A. Sluka, PhD, PT, Department of Physical Therapy and Rehabilitation Science, University of Iowa, Carver College of Medicine, 500 Newton Rd., 1–248 Medical Education Bldg, Iowa City, IA 52242. Address e-mail to kathleen-sluka@uiowa.edu.

© 2014 International Anesthesia Research Society