WASHINGTON, DC—Presentations at the American Pain Society's 26th Annual Scientific Meeting included new research on genetic factors associated with pain syndromes, on the possible use of nabilone for fibromyalgia, and on the intersection between chronic pain and chronic posttraumatic stress disorder (PTSD).

Shad B. Smith, PhD, of the Pain Genetics Lab at the University of North Carolina, in Chapel Hill, reports that certain changes in the α1A adrenergic receptor gene (ADRA1A) are associated with both neurological and psychological phenotypes that make temporomandibular joint disorder (TMJD) more likely.¹  He notes that individual variability in adrenergic system genes "may be a common determinant of both psychological and nociceptive phenotypes, as adrenergic pathways are known to mediate the response to environmental stress. Dr. Smith et al prospectively studied 183 initially healthy subjects who were followed over 3 years after being assessed for psychosocial traits, pain responses, and several candidate genes. He found strong associations between ADRA1A polymorphisms and alertness, anxiety, depression, and somatization, as well as sensitivity to noxious thermal and mechanical stimulation. Several of the alleles were linked to a nine-fold increase in risk of TMJD. He concludes, "Our findings indicate that ADRA1A variants may contribute to the vulnerability to develop an idiopathic pain condition, via increasing pain sensitivity and predisposition to psychological phenotypes that are associated with TMJD and related conditions."

Ryan Quinlan Skrabek, MD, and Lena Galimova, MD, conducted a randomized, double-blind, placebo-controlled trial in 40 fibromyalgia patients showing that the oral cannabinoid nabilone decreased pain, improved function, and decreased anxiety significantly more than placebo treatment.² However, the nabilone group also had significantly more side effects. The investigators conclude, "Nabilone appears to be a reasonable, well-tolerated treatment option in patients with fibromyalgia, with significant benefits in pain relief and functional improvement." Drs. Skrabek and Galimova are with the section of physical medicine and rehabilitation at the University of Manitoba, in Winnepeg, Canada.

Two hundred patients with chronic pain and chronic combat-related posttraumatic stress disorder (PTSD) were studied and reported to have better outcomes with reduced cost if treated in a multidisciplinary pain clinic, according to Marijana Bras, MD, and colleagues with the clinic for psychological medicine at University Hospital Centre Zagreb, in Croatia.³ Dr. Bras reports data on these two patient groups who were assessed using the Mississippi Scale for combat-related PTSD, the McGill Pain Questionnaire, the Pain Outcomes Questionnaire, the Brief Pain Inventory, and the Beck Depression Inventory. Patients who had comorbid depression had higher pain scores, and the affective component of pain correlated with the level of PTSD symptoms. Dr. Bras says that as with acute stress stimuli, hypersensitivity occurs in these patients, changing their perception of the world and "causing reaction to a nonnoxious stimulus."

Genetic and psychological factors combine to increase shoulder pain, according to lead researcher Steven Z. George, MD, and colleagues from the University of Florida, in Gainesville.⁴ Dr. George studied 58 patients seeking shoulder surgery. "Our a priori hypothesis was that we would detect a statistical interaction, such that subjects with high pain catastrophizing and a ‘high pain sensitive' COMT [catechol-O-methyltransferase] genotype would have the highest pain sensitivity," he writes. This proved to be generally true: there were statistically significant interactions between COMT haplotypes associated with high pain sensitivity and clinical pain ratings, thermal pain threshold, and pain tolerance, but not for pressure pain. Dr. George says that this provides preliminary evidence that specific psychological and genetic factors may influence shoulder pain sensitivity.

References

1. Smith S, Slade G, Belfer D, et al. ADRA1A polymorphisms associated with multiple psychological and nociceptive phenotypes predict vulnerability to an idiopathic pain condition. Presented at: American Pain Society 26th Annual Scientific Meeting; May 2-5, 2007; Washington, DC. Abstract #6822.
2. Skrabek R, Galimova L. A randomized double-blind placebo controlled trial assessing the effect of the oral cannnabinoid nabilone on pain and quality of life in patients with fibromyalgia. Presented at: American Pain Society 26th Annual Scientific Meeting; May 2-5, 2007; Washington, DC. Abstract #6964.
3. Bras M, Loncar Z, Janculjak D, et al. Neurobiological and clinical relationships between chronic pain and chronic posttraumatic stress disorder. Presented at: American Pain Society 26th Annual Scientific Meeting; May 2-5, 2007; Washington, DC. Abstract #7005.
4. George SZ, Wallace M, Wright T, et al. Evidence for biopsychocosial factors' influence on shoulder pain. Presented at: American Pain Society 26th Annual Scientific Meeting; May 2-5, 2007; Washington, DC. Abstract #6877.