Increased sensitivity to pain may be connected to cognitive problems that many fibromyalgia (FM) patients experience, according to a study linking pain perception with cognitive performance in the disease.
Researchers found that the response of patients to weak pain-evoking stimuli significantly reflected their cognitive difficulties, suggesting this is a better measure to address brain issues in fibromyalgia than other clinical tools.
The study, “Cognitive deficits in fibromyalgia syndrome are associated with pain responses to low intensity pressure stimulation,” was published in the journal PLOS ONE.
According to fibromyalgia patients, cognitive issues including forgetfulness, concentration problems, mental slowness, language-related problems, and reduced planning and decision-making abilities are among the most devastating symptoms of the disorder.
A number of studies support a close association between these cognition problems and enhanced pain sensitivity seen in these patients.
To address this link, researchers investigated the correlation between cognitive performance and pain threshold, pain tolerance, and pain response to low- and high-intensity pain-inducing stimuli, comparing them between fibromyalgia patients and healthy controls.
The study enrolled 42 women with fibromyalgia, recruited from the Fibromyalgia Association of Jaén in Spain, and 30 healthy women.
To evoke pain, researchers used a pressure algometer, an instrument with a screw-piston, which exerted controlled pressure on the fingernails of participants. Patients assessed how strong the pain was using a visual analogue scale (VAS), ranging from zero (not at all) to 10 (extreme).
Several cognitive tests involving a battery of tasks were applied to measure visuospatial and verbal memory, planning and organizational skills, processing speed, attention, and cognitive flexibility.
In line with previous findings, fibromyalgia patients had significantly lower pain thresholds (the point at which they started to feel pain) and lower pain tolerance (the maximum tolerated pressure) than healthy individuals.
Pain intensified with increasing pressure in both groups, but those with fibromyalgia were more sensitive, displaying a steeper increase in how much pain they felt.
Of note, fibromyalgia patients rated as painful very low pressure intensities, and significantly more than healthy participants.
Such hypersensitivity reflects two phenomena that characterize fibromyalgia: hyperalgesia — increased sensitivity to a noxious stimulus — and allodynia —a painful feeling in response to a stimulus that normally does not cause pain.
Importantly, neither pain threshold nor pain tolerance correlated with patients’ cognitive scores, regardless of the cognitive dimensions analyzed.
However, increased pain perception was significantly associated with poorer cognitive performance of patients, in particular, in those who felt pain at lower pressure intensities.
Impairments in all cognitive domains measured — attention, memory, and executive functions — significantly correlated with higher pain perception, a relationship that was stronger overall for pain evaluations done in lower pressure conditions.
This observation “underlines the closer relationship of pain responses to low stimulation intensities with cognitive impairments,” the researchers wrote.
“We hypothesize those pain responses, especially those to low stimulation intensities, reflect allodynia and central-nervous sensitization to pain,” they added.
Brain changes resulting from the process of sensitization may also lead to cognitive impairment, affecting attention, memory, and executive functions. Fibromyalgia patients may also experience a state of hypervigilance that may contribute to the amplification of body sensations, according to the researchers.
The study shows that pain experienced during stimulation at a low intensity is more closely related to cognitive issues in fibromyalgia patients than the traditional measures of pain threshold and pain tolerance.
“Pain reports during low intensity stimulation may be a useful measure in future studies on hypervigilance, perceptual amplification or deficits in somatosensory information processing in chronic pain,” the authors concluded.