Ingrid Hein

October 25, 2018

Patients who suffer chronic lower back pain, particularly those on sick leave, might have different mechanisms of pain control in the brain, results from a study of functional MRI show.

Researchers at the American College of Rheumatology 2018 Annual Meeting in Chicago reported a weaker functional MRI signal in emotion-related areas of the brain in patients with chronic back pain who were on sick leave than in patients with chronic back pain not on sick leave and in asymptomatic patients.

Although there was no distinction in brain activity between the three groups in brain areas related to acute pain, the back pain patients on sick leave tended to be less distracted from pain in attention tests, showing a reduced fMRI signal in emotion-related brain areas.

“We hypothesize that these areas of the brain might already be chronically activated in individuals on sick leave,” said Ari Halpern, MD, from the Instituto do Cérebro, Hospital Israelita Albert Einstein and the Hospital das Clinicas da Universidade de São Paulo.

They could be constantly experiencing a heightened perception of pain, he told Medscape Medical News.

Source of Pain Difficult to Pinpoint

On clinical exam, patients with chronic lower back pain “often don’t have any structural damage; we cannot find any radiological features to explain the source of the pain, said Halpern.

This makes them difficult to treat, he explained. These patients often don’t respond well to anesthetics, physiotherapy, or standard pain killers directed at musculoskeletal pain.

The latter is particularly true for patients with back pain who are on sick leave, Halpern reported, “so we wondered whether there are specific characteristics in the physiology of the brain in this group.”

He and his colleagues divided 74 study participants into three groups: patients with chronic lower back pain who were on sick leave; patients with chronic lower back pain not on sick leave; and control subjects without chronic lower back pain.

The researchers applied pressure-invoked acute pain, rather than spontaneous back pain, at a neutral site (the thumb).

Using functional MRI, which visualizes changes in cerebral blood flow when neurons in the brain are activated, the researchers looked at the brains of the study participants before and after stimulation with acute pain.

“We saw an alteration in the neuroplasticity of chronic back pain patients in brain areas that are not the sensory regions,” said Halpern.

Blood flow activation in the sensory regions of the brain was lower in the sick-leave group than in the control group. In the back pain patients not on sick leave, there was some activation, but it was much less than in the control group.

“Those on sick leave had less activation in the brain than those not on sick leave,” Halpern reported. “We think this means that those areas of the brain are already prone to be active in the group on sick leave.”

Emotional Centers Stimulated

This study confirms that chronic pain is associated with altered neuronal plasticity in brain areas that extend beyond somatosensory regions and include areas that process emotions, as has been shown in previous studies, the researchers write in their abstract.

Because pain is influenced by genetic, pathologic, cognitive, and emotional aspects, this offers evidence that mechanisms of pain control in the brains of patients with chronic pain might be altered. . “We think the modulation of acute pain participates in the mechanism propagating chronic pain perception,” Halpern said.

The research does not address whether the change in neuroplasticity occurred before or after the patient went on sick leave, he acknowledged. “But we do know from many studies published that the longer the sick leave, the lower the chance that patients go back to work, and the lower the chance that they recover from the back pain.”

However, the research does show that it is important to look at different subgroups of patients with chronic lower-back pain, he said. “We have to consider the physiopathology of each group of patients. A lot more happens in the brain than we ever thought.”

Halpern has disclosed no relevant financial relationships.

American College of Rheumatology (ACR) 2018 Annual Meeting: Abstract 449. Presented October 21, 2018

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