Comorbid Conditions Receive Focus

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Suzanne Vernon, PhD, is the Association’s scientific director.

By Suzanne Vernon, PhD, Scientific Director

The TMJ (temporomandibular joint) Association invited me to participate in their Fifth Scientific Meeting, held at the Federation of American Societies for Experimental Biology in Bethesda, Maryland, from June 1-3, 2008. The objective of the meeting was to determine if studies of disorders often comorbid with TMJ could reveal common mechanisms of disease. I was invited to discuss CFS because it’s often comorbid with TMJ disorders.

Morbid means sickness or induced by disease. Comorbidity refers to the presence of one or more disorders or diseases in addition to a primary disease. Like CFS, TMJ disorders are characterized by clinically recognizable features (symptoms) that often occur together. Disorders that commonly co-occur with TMJ include CFS, fibromyalgia, headache/migraine, interstitial cystitis, vulvodynia, endometriosis, arthritis and functional gastrointestinal disorders. Common to each of these disorders is fatigue, pain, sleep disturbance and cognitive impairment.

By understanding the mechanisms for each of these signs and symptoms, we can identify the molecular underpinnings these disorders share and what makes each unique. For example, by studying mechanisms of fatigue, treatment strategies targeted at the fatigue could impact a broad range of disorders that have fatigue as a major symptom.

There is some literature implicating commonalities among comorbid conditions:

  1. Chronic fatigue, chronic widespread pain, chronic orofacial pain and irritable bowel syndrome have been found to co-occur in the general population and share common associated factors such as age and gender.
  2. Similar endocrine disturbances have been identified in CFS and fibromyalgia; both display low cortisol and hypothalamic-pituitary-adrenal (HPA) axis dysfunction.
  3. Similar cerebral spinal fluid protein profiles occur in CFS, fibromyalgia and Gulf War illness.

Up until last month, there haven’t been many publications attempting to identify common or distinct mechanisms among these comorbid conditions. But a very interesting article was published by Kenji Kato, PhD, and colleagues in the June issue of Psychological Medicine that does exactly this. The paper identifies common and distinct genetic and environmental factors that influence four functional somatic syndromes—chronic widespread pain, chronic fatigue, irritable bowel syndrome and recurrent headache—and two psychiatric disorders—major depression and generalized anxiety disorder.

This paper is important but not an easy read for those unaccustomed to the jargon of twin studies and the mathematics of structural equation modeling. So in “New Findings about Comorbid Conditions,” I try to break the paper down to a few, more easily digested take-home messages. Kudos to Kato and his coauthors for a solid study and one of the first in what is hopefully a series that reveals the environmental and genetic influences and mechanisms of CFS and comorbid conditions.

Suzanne Vernon, PhD, is the Association’s scientific director. She has nearly two decades of experience as a microbiologist.

July 1, 2008