Functional Disease

The term “functional disease” means different things to different people. Dr. Boles uses the term in a similar manner to that it is commonly used by gastroenterologists (GI), and not how it is commonly used by some neurologists. In the GI context, and the one used in this website and practice, functional disease refers to any condition that results from the abnormal function of cells, tissues, and organs, and not the abnormal structure of cells, tissues, and organs. Thus, in GI, gastoesophageal reflux disease (GERD), cyclic vomiting, and irritable bowel syndrome (IBS) are functional conditions. On the other hand, esopheageal scars, volvulus (twisting of the intestines causing blockage), and colon cancer are structural conditions.

In this usage, the term “functional” does not infer that it is psychiatric, fictitious, non-organic, or any other term to suggest that disease is not real. Unfortunately, this term does have this connotation to some physicians, especially in neurology, but that is changing. While functional disease is not really a great term, Dr. Boles is not aware of a better term. In Dr. Boles’ mind, functional disease is just as real as structural disease. However, it is far more difficult to diagnosis. It is also far more common than structural disease, at least in children and young adults.


A partial list of recognized functional conditions includes:

  • Attention deficit hyperactivity disorder
  • Anxiety disorder
  • Autistic spectrum disorders
  • Chronic fatigue syndrome
  • Complex regional pain syndrome
  • Cyclic vomiting syndrome
  • Depression (MDD)
  • Fibromyalgia
  • Functional abdominal pain
  • Interstitial cystitis
  • Insomnia (chronic, severe)
  • Irritable bowel syndrome
  • Migraine
  • Panic disorder
  • Post-traumatic stress disorder
  • Postural orthostatic tachycardia syndrome
  • Restless legs syndrome
  • Temporomandibular disorder
  • Tinnitus
  • Vulvovaginitis syndrome

The functional disorders can be found alone, but it is common to find more than one, often several, in the same patient. They also are frequently found clustered in families.


PHOTO: From the old proverb from India, three blind men felt different parts of the same elephant and describe three different animals. Image these as physicians, each focused on their own specialty, evaluating different parts of the same patient. The ENT gives a diagnosis of tinnitus, the cardiologist of POTS, and the gastroenterologist as irritable bowel. However, all are simply different manifestations of the functional disease, and no one has found the underlying cause or factors.

Many of the functional disorders are triggered and get worse with stress. Many of the structural disorders do as well. This does not infer that disease is caused by stress or that the disease will vanish once stress is handled better. However, for a wide range of disorders, functional included, improved dealing with stress can help, especially as part of a comprehensive management approach that also addresses the root causes of illness.

For over two decades, Dr. Boles has been committed to understanding the factors that lead towards functional disease, in order to lead to improved therapies.