Thenar muscles H reflex in patients with fibromyalgia: A case control study.

To delineate H-reflex parameters and specify the diagnostic accuracy measures of thenar muscle H-reflex in Fibromyalgia (FM).The study was a cross sectional study performed on 30 subjects with FM and 30 healthy volunteers in two major referral hospitals. We recorded the number of obtainable thenar H-reflexes and their minimum latency, threshold and amplitude in each group.There was a significantly more chance to elicit the H-reflex in patients with FM. H reflex threshold and minimum latency were lower in FM group but no significant difference was shown for H wave amplitude. According to our study, thenar H-reflex has 46.7% sensitivity, 86.7% specificity and 66.7% diagnostic accuracy to detect FM. It also has moderate predictive values and positive likelihood ratio but low negative likelihood ratio.Higher rate of thenar muscle H-reflex in fibromyalgia can be interpreted as a confirmatory finding to central sensitization theory for this disorder. Obtaining H-reflex from thenar muscles could be a helpful diagnostic tool for fibromyalgia that increases the confidence in diagnosis. Although it is a weak tool for screening because of low sensitivity, it has a relatively high specificity.