The old belief that OCD was the result of life experiences has been weakened before the growing evidence that biological factors are a primary contributor to the disorder. The fact that OCD patients respond well to specific medications that affect the neurotransmitter serotonin suggests the disorder has a neurobiological basis. For that reason, OCD is no longer attributed only to attitudes a patient learned in childhood–for example, an inordinate emphasis on cleanliness, or a belief that certain thoughts are dangerous or unacceptable. Instead, the search for causes now focuses on the interaction of neurobiological factors and environmental influences, as well as cognitive processes.
OCD is sometimes accompanied by depression, eating disorders, substance abuse disorder, a personality disorder, attention deficit disorder, or another of the anxiety disorders. Co-existing disorders can make OCD more difficult both to diagnose and to treat.
In an effort to identify specific biological factors that may be important in the onset or persistence of OCD, NIMH-supported investigators have used a device called the positron emission tomography (PET) scanner to study the brains of patients with OCD. Several groups of investigators have obtained findings from PET scans suggesting that OCD patients have patterns of brain activity that differ from those of people without mental illness or with some other mental illness.
Brain-imaging studies of OCD showing abnormal neurochemical activity in regions known to play a role in certain neurological disorders suggest that these areas may be crucial in the origins of OCD. There is also evidence that treatment with medications or behavior therapy induce changes in the brain coincident with clinical improvement.
Recent preliminary studies of the brain using magnetic resonance imaging showed that the subjects with obsessive-compulsive disorder had significantly less white matter than did normal control subjects, suggesting a widely distributed brain abnormality in OCD. Understanding the significance of this finding will be further explored by functional neuroimaging and neuropsychological studies (Jenike et al, 1996).
Symptoms of OCD are seen in association with some other neurological disorders. There is an increased rate of OCD in people with Tourette’s syndrome, an illness characterized by involuntary movements and vocalizations. Investigators are currently studying the hypothesis that a genetic relationship exists between OCD and the tic disorders.
Other illnesses that may be linked to OCD are trichotillomania (the repeated urge to pull out scalp hair, eyelashes, eyebrows or other body hair), body dysmorphic disorder (excessive preoccupation with imaginary or exaggerated defects in appearance), and hypochondriasis (the fear of having–despite medical evaluation and reassurance–a serious disease). Genetic studies of OCD and other related conditions may enable scientists to pinpoint the molecular basis of these disorders.
Other theories about the causes of OCD focus on the interaction between behavior and the environment and on beliefs and attitudes, as well as how information is processed. These behavioral and cognitive theories are not incompatible with biological explanations.