In a well-argued review appearing in the leading science journal, Nature, investigators from the University of North Carolina, Chapel Hill suggest that both the diagnosis and treatment of TMD and other musculoskeletal pain conditions would benefit if health care providers conducted a number of physiological and psychological tests on patients, rather than just measuring pain and dysfunction in the jaws or lower back or wherever else patients report musculoskeletal pain. And by “psychological” they don’t mean tests to label a patient as neurotic; they mean tests that measure such phenomena as “somatic awareness”—your perception and interpretation of information from your senses—as well as tests that measure anxiety, depression, and perceived stress. Analyzing the results of a range of tests can result in a pain profile, a kind of personal signature that specifies you have a particular subtype of TMD or fibromyalgia or other musculoskeletal pain.
The researchers base their reasoning on studies showing that the risk for TMD, fibromyalgia, low back pain, and a condition called chronic widespread pain is highly associated with two factors: pain amplification, meaning that the individual has increased pain sensitivity, and psychological distress, including somatic awareness and the psychological states described earlier. Indeed, somatic awareness is emerging as a potent predictor of musculoskeletal conditions, since it is a means by which pain and other sensory phenomena, as well as feelings of anxiety, depression and stress are amplified.
The investigators are team members of the OPPERA (Orofacial Pain Prospective Evaluation and Risk Assessment) program, the long-running clinical study aiming to explain who gets TMD and why. In the current study, led by Luda Diatchenko, the researchers reviewed the literature on epidemiology, genetics, and environmental factors for the four named conditions (TMD, chronic low back pain, fibromyalgia, and chronic widespread pain). They note that an individual’s genetic background is influenced by environmental factors to produce what they call intermediate phenotypes. The “phenotype” is the unique person you are as the result of how your genes interact with your environment, e.g., you are 5' 2", brown eyes, with high blood pressure, and so on. An intermediate phenotype would be the foreshadowing of what you become (and the pains you may experience) based on your genetic make-up and the environmental influences that affect how your genes turn on and off in the course of your development. For example, whether an individual experienced nutritional deficiencies in infancy.
If this sounds complicated, it is. But the neat trick is that tests are available to measure those intermediate phenotypes. For example, quantitative sensory testing can record whether you are more or less sensitive to heat, touch, pressure and other sensory modalities; genetic testing can determine whether you have inherited one or more common or rare gene variants that make you more or less sensitive to pain. There are also tests of your autonomic nervous system, concerned with fight or flight reactions, as well as digestion, heart rate, and so on. When the results of multiple tests are looked at in relation to patients who have been diagnosed with TMD or low back pain or another musculoskeletal condition, it is possible to identify subpopulations of patients with the disease in question who share the same gene variants, for example, or who have similar scores in various tests.
Not only does this establish new scientific diagnostics for TMD diagnosis, but it offers hope for targeted therapies—maybe a chemical that will alter a gene’s expression or affect some biological pathway that has disrupted autonomic nervous system function. You may have read about this approach in other contexts: It is a step toward creating customized or personalized medicine, a treatment that suits you to a T(MD)!
by Joan Wilentz, The TMJ Association
Source:Luda Diatchenko, Roger B. Fillingim, Shad B. Smith & William Maixner.The phenotypic and genetic signatures of common musculoskeletal pain conditions. Nature Reviews Rheumatology 9, 340-350 (June 2013) | doi:10.1038/nrrheum.2013.43