RSDM Researchers Explore How Pain Becomes Chronic

Dr. Cibele Nasri-Heir

When acute pain becomes chronic, there’s a turning point. Changes occur in the body that allow the hurt to continue -- even after the original source of pain is gone. “In these cases, the pain becomes the disease,’’ says Dr.Cibele Nasri-Heir, an Assistant Professor at RSDM’s Center for Temporomandibular Disorders and Orofacial Pain.

“The patient’s injuries may have healed, everything looks normal, but the pain continues,'' she explained.

Scientists don’t know how or why pain switches from acute to chronic. But Nasri-Heir and a team of RSDM researchers led by former faculty member Dr. Eli Eliav,  now at the University of Rochester, have discovered important clues.

Their results suggest that chronic pain may stem from a breakdown in the body’s ability to block or reduce the perception of pain, said Nasri-Heir. In a study of patients scheduled for publication in PAIN, the top journal in the field of pain research, the team found evidence that pain can become chronic due to a deficiency of the body’s pain inhibitory system, which controls the perception of pain. They also discovered the deficiency was more pronounced in patients who complained of pain for longer than a year.

“This could reflect the transition of the central nervous system from acute to chronic pain,’’ said Nasri-Heir, who who collaborated on the research with Rutgers Health University Dental Associates doctor and professor Gary Heir, Director of the Division of Temporomandibular Disorders and Orofacial Pain at RSDM.

Her team's research, funded by a $429,000 grant from the National Institutes of Health, examined dental patients who suffer from post-traumatic trigeminal neuropathy (PTTN), which includes prolonged pain caused by nerve injury associated with endodontic or surgical procedures, such as root canals and tooth extractions.

Symptoms related to PTTN, a condition that effects up to seven percent of post-endodontic patients, include moderate to severe burning pain after otherwise successful treatment. "It’s a condition that’s difficult to treat since it doesn’t respond to commonly prescribed analgesics or anti-inflammatories,” said Nasri-Heir.

Her team’s findings could greatly help with treatment since studies have shown that some medications can reduce certain types of chronic pain by targeting and strengthening the pain inhibitory system.

As part of RSDM’s pain research, participants were given two types of stimuli to test the pain modulatory system, which controls whether pain perception is increased or decreased. One test involved the facilitatory system, which detects the enhancement of the nerves’ response to stimulus. The other is associated with the pain inhibitory system, which helps the body diminish feelings of pain.

Patients with long-term pain lasting more than one year reported less pain as a result of facilitation, but more pain in the test linked with an inefficiency of the pain inhibitory system

Dr. Nasri-Heir’s research also reveals that some patients have a propensity to develop chronic pain and explores how it can be measured and detected so that treatment plans can be tailored to the individual patient. “If we can identify risk factors for patients who might be likely to develop chronic pain after surgical procedures, we can create strategies that might avoid post-operative suffering," she said.

A second phase of the test will explore genetic factors that could govern the predisposition to develop chronic pain.

Departments at RSDM participating in this study included Diagnostic Sciences, Endodontics and Oral Biology/ Center for Pharmacogenomics and Complex Disease Research.