Functional disorder

A functional disorder is a medical condition that impairs normal functioning of bodily processes that remains largely undetected under examination, dissection or even under a microscope. At the exterior, there is no appearance of abnormality. This stands in contrast to a structural disorder or a psychosomatic disorder. Definitions vary somewhat between fields of medicine.
Generally, the mechanism that causes a functional disorder is unknown, poorly understood, or occasionally unimportant for treatment purposes. The brain or nerves are often believed to be involved. It is common that a person with one functional disorder will have others.

1. Status
Whether a given medical condition is termed a functional disorder depends in part on the state of knowledge. Some diseases, including epilepsy, schizophrenia, and migraine headaches were once considered functional disorders, but are no longer generally classified that way.

2. Examples
Interstitial cystitis
Temporomandibular joint pain, functional neurological symptom disorder
Cyclic vomiting syndrome
Chronic pelvic pain
Irritable bowel syndrome
Chronic fatigue syndrome