A recent paper published in BMC Neurology journal entitled “Increased cortical activation upon painful stimulation in fibromyalgia syndrome” provides evidence that fibromyalgia syndrome (FMS) is a distinct pathophysiology from the spectrum of major depression.
Though exact causes of FMS are unknown, a combination of genetic and factors like stress, food sensitivity, and sleep disturbance have been pointed out to contribute for FMS development. Patients with FMS often complain of chronic widespread pain, fatigue, sleep disturbance, cognitive impairment, and changes in mood. It is believed that FMS often co-occurs with major depression; however, there is ongoing debate on whether FMS is a district pathophysiology or a variant of depression.
From a mechanistic point of view, some hypotheses suggest that patients with FMS have elevated reactivity of pain-sensitive brain nerve cells when compared to healthy controls. Medical methods like radiological and nuclear medicine have been used to clarify possible morphological or functional alteration in the brains of FMS patients. Each method has its advantages and drawbacks in terms of complexity and invasiveness. In the present study, researchers explored an imaging technique called functional near-infrared spectroscopy (fNIRS) as a means to investigate brain activation in people with FMS. When compared to radiological and nuclear medicine methods, fNIRS is an easy and practical tool without side effects.
A total of 25 FMS patients, joined by 10 with unipolar major depression without pain and 35 healthy controls, participated in the study. Age, gender, and educational background were matched between FMS patients and controls. The subjects were evaluated using two methodologies: 1) fNIRS scans during painful pressure stimulation at the dorsal forearm, and 2) a verbal fluency test (VFT), where participants were asked to produce as many nouns as possible during periods that lasted 30 seconds, followed by 30 seconds of rest. Prior to evaluation, FMS patients performed neurological tests and all subjects filled in a questionnaire related to pain, depression, FMS, and empathy. Afterward, all data were analyzed by means of appropriate software and models.
The results suggested that when compared to patients with major depression and healthy controls, FMS patients had weaker pressure pain thresholds and suffered from higher pain intensities. When the participants were subjected to pressure pain stimulation, fNIRS scans showed strong brain activation in FMS patients when compared to the other two study groups. Finally, when results from VFT were compared with fNIRS scans, a positive correlation was only recorded in patients with depression where deficit brain activation corroborated results from the VFT test.
These findings demonstrate that patients with FMS subjected to pressure pain stimulation have a distinctive pattern of brain activation when compared to patients with major depression or to healthy controls, suggesting that, contrary to previous beliefs, FMS could be considered as an independent entity rather than a variant of depression.