Patients with fibromyalgia show a poorer ability for “selective learning” of pain triggers, which may contribute to their widespread pain, a study reports.
The study, “Reduced selective learning in patients with fibromyalgia vs healthy controls,” was published in the journal Pain.
Pain episodes can occur at the same time as other non-painful stimuli, which can result in spreading of fear and persistent anxiety. Although identifying causes of pain is key, discriminating actual pain predictors from other stimuli can be challenging.
Research shows that individuals with chronic pain have impaired selective “fear” learning. The litmus test of selective learning is the blocking procedure, which consists in pairing one event with pain in the first stage, followed by pairing a different, non-painful event with the original pain-inducing stimulus.
When testing non-painful stimulus alone, fear response is normally weak or blocked despite its previous association with pain. Selective learning may be compromised, as described in people with high anxiety.
Aiming to study whether patients with fibromyalgia have a poorer evidence of selective threat learning compared to healthy individuals, researchers used a clinical diary to develop a five-phase selective learning task.
A total of 27 patients with fibromyalgia (26 women, mean age 46) and 27 healthy controls rated six scenarios from 0 (“certainly no pain”) to 10 (“certainly pain”) based on whether they expected those situations to trigger pain on a fictional fibromyalgia patient, called Kim.
According to the researchers, such a strategy enables evaluating selective learning without inducing pain or worsening patients’ symptoms.
The situations covered different types of possible pain triggers – “Kim was stressed” (emotional distress trigger), “Kim has vacuumed” (activity-based), “Kim slept badly” (physical), and “the weather was bad today” (environmental). Two situations were were presented during a practice phase (the second phase) only – “Kim had a marital dispute” (social) and “Kim has walked the dog” (activity-based).
Initial assessments showed that while fibromyalgia patients reported expecting to experience pain in all six situations, healthy controls did not view these situations as painful.
Four different phases were designed to associate specific situations with pain (stimuli A and, later, B) and others with no pain (Z). One such stimulus (X) was presented at the same time as A. As participants had learned that A predicted pain, X was redundant and was expected to be blocked, according to the investigators.
In the test phase, participants underwent three trials with one presentation of B, Z and X each in a random order, one not followed by an indication of pain or no pain outcomes.
Participants completed the task at home. They then answered questionnaires to assess pain disability, pain intensity and interference in daily life, fear of pain, positive and negative emotions, attention, fear of movement, and pain-related cognitive aspects such as trust, optimism and catastrophizing – believing symptoms are worse than they are.
Pretest phases showed that fibromyalgia patients and controls had no difference in discriminating between pain- and no pain-related stimuli.
But the test revealed that, unlike controls, people with fibromyalgia did not show blocking, as evidenced by no differences in pain expectancy judgments between the pain-associated B stimulus and the blocked X stimulus.
These result were not affected by patients’ views on whether the stimuli would cause them pain, the scientists noted.
Of note, all questionnaires showed differences between patients with fibromyalgia and healthy controls, except those related to fear of pain.
“To conclude, this study provides direct, yet partial evidence for impaired selective learning in patients with [fibromyalgia],” the researchers wrote. They added that this may contribute to the transition from localized to widespread pain in these patients.