With up to 50% of whiplash patients developing chronic symptoms, researchers have continued to ask, “Why do certain people develop chronic whiplash pain while others do not?” A new study provides a potential clue into answering that question: cytokines.
Cytokines are proteins secreted by cells of the immune system which aide in cell communication. Immediately after an injury, the immune system produces pro-inflammatory cytokines responsible for fighting off infection. Although whiplash itself is a traumatic event, few studies have examined the role that inflammatory chemicals play in whiplash injuries.
New research published in PLoS One shows that patients who recover more quickly from whiplash tend to have certain changes in cytokine levels that chronic whiplash patients do not.
Leading whiplash-researcher Michele Sterling of the University of Queensland in Australia and her colleagues studied how cytokine levels fluctuate in whiplash patients over time. They studied 40 patients within 2-3 weeks after sustaining a whiplash injury, and compared them to 18 healthy controls. Participants were evaluated for disability level, hyperalgesia (pain sensitivity), pain scores, and psychological symptoms. Researchers also collected serum blood samples to evaluate cytokine levels, and took MRI scans to pinpoint the development of muscle fatty infiltrates indicative of morphological muscle changes. Typically, it becomes apparent whether or not a patient will develop chronic symptoms within 2-3 months post injury, so researchers took initial tests and conducted follow-up tests three months later.
At first, all whiplash patients had higher levels of a pro-inflammatory cytokine called C-reactive protein (CRP), which is a signal of overall inflammation in the body. Three months after the injury however, some of the patients had reduced CRP levels. These patients were also the ones who were more likely to recover.
Patients with better recovery rates also continued to have elevated levels of a cytokine called TNF-α. This was surprising since the presence of pro-inflammatory cytokines usually signals increased inflammation. However, the researchers also found that patients with higher TNF-α levels at three months seemed to have fewer muscle fatty infiltrates. They speculated that increased initial TNF-α levels may have actually facilitated muscle recovery.
The researchers also discovered that higher CRP levels were correlated with reduced pain tolerance, and that none of the inflammatory biomarkers measured significantly correlated with psychological symptoms. They speculated that the lack of correlation between inflammatory biomarkers and psychological symptoms may have been because only 20% of the patients had symptoms of PTSD. Other research of patients with more severe PTSD symptoms has pointed to a relationship between inflammatory biomarkers and psychological symptoms.
If this research is confirmed in future studies, tracking changes in inflammatory biomarkers using serum blood tests may offer clues into determining a patient’s risk of chronic symptoms.
Sterling M, Elliot JM, Cabot PJ. The course of serum inflammatory biomarkers following whiplash injury and their relationship to sensory and muscle measures: a longitudinal cohort study. PLoS One 2013. 8(10):e77903. doi: 10.1371/journal.pone.0077903.