Immune disorder eosinophilia may hold key to chronic pain, University of Arizona study finds

University of Arizona researchers have reported a potential link between chronic pain and the immune disorder eosinophilia, suggesting the condition may serve as a biomarker for inflammation in pain patients

A research team at the University of Arizona, Tucson, United States, has reported a potential connection between chronic pain and an immune condition which suggests a route to identify immune biomarkers that could improve diagnosis and treatment of chronic pain.

A small retrospective study led by Professor Julie Pilitsis, chair of neurosurgery at the University of Arizona College of Medicine in Tucson, found that 12% of patients with chronic pain treated using spinal cord stimulation or implanted intrathecal pain pumps had a white blood cell abnormality known as eosinophilia. The condition, typically seen in fewer than 1% of the general population, arises when the immune system malfunctions and produces excessive numbers of eosinophils.

Although patients with eosinophilia did not appear to respond differently to pain therapy, the study revealed a possible relationship between chronic pain and immune dysregulation. Professor Pilitsis, who is also a member of the University’s Comprehensive Centre for Pain and Addiction, said the discovery had strengthened the view that chronic pain involves an inflammatory component.

Eosinophilia is characterised by abnormally high levels of eosinophils – white blood cells that defend the body against various pathogens. It has previously been associated with autoimmune disorders and other chronic inflammatory diseases.

“Few studies have examined a connection between eosinophilia and pain,” said Professor Pilitsis.

“We are always looking for risk factors to identify and modify which ideally could help us predict who will respond best to chronic pain treatment.”

According to the United States’ Centers for Disease Control and Prevention, more than 24% of adults experience chronic pain and around 8.5% live with high-impact chronic pain that interferes with daily life. Patients who undergo spinal cord stimulation or receive an intrathecal pain pump typically belong to this group.

A spinal cord stimulator is an implanted device that delivers small electrical impulses to the spinal cord to interrupt pain signals, while an intrathecal pump delivers medication directly into the cerebrospinal fluid surrounding the cord.

The research team reviewed medical records from 212 patients who had received one of these two treatments for high-impact chronic pain. Of these, 114 patients had undergone routine blood testing within a month of treatment. Analysis revealed that 14 of the 114 patients – approximately 12% – exhibited eosinophilia prior to their procedure.

“The condition typically affects fewer than one in a hundred people [but] we found a markedly higher incidence,” Professor Pilitsis said.

“Now we are asking whether eosinophilia predisposes someone to chronic pain, and if it could serve as a biomarker before and after treatment to show if therapy reduces inflammation,” she added.

Around 70% of spinal cord stimulation patients reported some degree of pain reduction. Professor Pilitsis said it remains unclear whether eosinophilia might indicate how well a patient will respond to therapy, or whether inflammation could be a modifiable factor.

She also noted that autoimmune conditions such as rheumatoid arthritis did not appear to correlate with eosinophilia in the cohort.

“It is speculative at this stage but for those who do not respond well to treatment, we might consider adding an anti-inflammatory component. We still have many questions,” she concluded.

For further reading please visit: 10.1016/j.neurom.2025.07.004