Altered spinal excitability in patients with primary fibromyalgia: A case-control study

Abstract

Background and Purpose Abnormal excitability of the central nervous system, both spinal and supraspinal, has previously been described as a pathophysiological plastic mechanism for chronic pain syndromes. Primary fibromyalgia (FM) as one extreme of this spectrum of dis-eases. This case-control study aimed to determine the changes in the spinal excitability by in-vestigating the Hoffman reflex (H-reflex) in patients with FM. Methods Thirty-eight patients with FM and 30 healthy controls participated in this case-con-trol study. We measured the H-reflex bilaterally in the upper limbs (flexor carpi radialis) and the lower limbs (gastrocnemius and soleus). Moreover, pain-related variables were measured, including pain severity (using a visual analogue scale), pain duration, Widespread Pain Index, and the score on the Symptom Severity Scale. Various psychiatric comorbidities and quality-of-life parameters were measured for each patient, including scores on the Hamilton Depression Rating Scale, Taylor’s Manifest Anxiety Scale, and the Revised Fibromyalgia Impact Ques-tionnaire. Results A significant increase in the ratio of the maximum baseline-to-peak amplitudes of H and M waves (Hmax/Mmax) but not in the H-wave minimum latency was found in patients with FM compared with healthy controls. There were no significant correlations between this ratio in both muscles and the various pain-related measures, psychiatric comorbidity, and quality of life in patients with FM. Patients with FM suffered more depression and anxiety than did the controls. Conclusions We found increased spinal excitability in patients with FM, which was not con-fined to the site of maximum pain. This information may help in the diagnosis of FM and sup-ports the hypothesis of central sensitization.