An unexpected link has been found between chronic pain and the state of immunity

Researchers from the University of Arizona have discovered an unexpected connection between chronic pain and a rare immune condition - eosinophilia, in which the blood has elevated levels of eosinophils, a type of white blood cell. The work is published in the journal Neuromodulation: Technology at the Neural Interface (NTNI).

The team led by Professor Julie Pilitsis, chair of the Department of Neurosurgery at the University of Arizona College of Medicine in Tucson, analyzed medical data from 212 patients who were undergoing treatment for chronic pain using spinal cord stimulation or implanted systems for delivery of pain medication. Eosinophilia was found in 12% of patients with chronic pain - whereas in the general population this condition occurs in less than 1% of people.

Eosinophils play a key role in protecting the body from allergens, fungi, and parasites, but their excess can be a sign of disruptions in the immune system, including autoimmune and chronic inflammatory diseases.

"Previously, the possible connection between eosinophilia and pain was virtually unstudied," noted Pilitsis. "We are constantly looking for risk factors that could help predict the development of chronic pain or the effectiveness of treatment."

Chronic pain, according to the researchers, is increasingly being viewed as a condition with a pronounced inflammatory component. According to the Centers for Disease Control and Prevention of the USA, about 24% of adult Americans suffer from chronic pain, and 8.5% - from pain that significantly limits their daily activities.

The patients who participated in the study belonged to this latter group: they required surgical treatment - implantation of a spinal cord stimulator (a device that delivers weak electrical impulses to the spinal cord to reduce pain) or an intrathecal pump that delivers pain medication directly into the cerebrospinal fluid.

Of 114 patients who had blood tests taken a month before surgery, 14 (12%) showed elevated levels of eosinophils.

About 70% of patients with spinal cord stimulation report a reduction in pain, however it is not yet known whether this method can reduce inflammation.

"If it is confirmed that eosinophilia is linked to chronic pain, this will help more accurately determine for whom the treatment will work better, and for whom - worse," added the researcher.