Q. Is Huntington's Disease a psychiatric disorder or is it a neuropsychiatric disorder? What is the difference between the two?

A. That's a good and an important question--but it's a bit like asking if asking if George W. Bush is a republican, or a republican president. That is to say, Huntington's Disease (HD)--sometimes called Huntington's Chorea--lies within the subset of psychiatric disorders called neuropsychiatric disorders. HD is found in the "bible" of clinical psychiatry, the DSM-IV (Diagnostic & Statistical Manual of Mental Disorders, 4th ed.), but is also found in any respectable textbook of clinical neurology.

What characterizes this subset of conditions, generally speaking, are the following features: 1. There is usually gross brain pathology visible under a microscope or other imaging technique, such as a CT scan; 2. The clinical and neurological examination often shows observable motor impairment, or else cognitive abnormalities, such as impaired memory and calculation; and 3. Historically, these disorders have been managed primarily by neurologists, rather than psychiatrists (though this is changing, as more doctors consider themselves neuropsychiatrists). Other examples of neuropsychiatric disorders are Alzheimer's Disease and Parkinson's Disease.

The three features I listed are very rough differentiating criteria, though, and many exceptions could be pointed out. The problem is, the more we learn about regular psychiatric disorders--those not usually deemed neuropsychiatric--the more this rather artificial boundary breaks down. For example: in Huntington's Disease, an area of the brain called the basal ganglia is clearly abnormal. This part of the brain mediates certain types of involuntary movements, such as shaking or tremors. But the basal ganglia also appear to be involved in certain types of repetitive behaviors and thoughts, of the sort one sees in obsessive-compulsive disorder (OCD). And guess what? Abnormalities of the basal ganglia have been seen in both OCD and in schizophrenia! So which of these disorders is neuropsychiatric and which, just plain old "psychiatric?

It's getting harder and harder to say, the more we discover about these conditions-which is just another way of saying that the mind/brain dichotomy put forth by Rene Descartes is becoming more and more untenable. For much more on these issues, I highly recommend the excellent textbook edited by S. Yudofsky and R. Hales, The American Psychiatric Press Textbook of Neuropsychiatry, 3rd edition.

July 2002

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