'Not Otherwise Specified' (NOS) in the Diagnosis of Mental Disorders

How This Term Was Used in the Fourth Edition of the DSM

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In the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), which was written and issued by the American Psychiatric Association (APA), "NOS" is an abbreviation for "not otherwise specified." It serves as a sort of catch-all term to label symptoms that don't neatly fall into a well-defined diagnosis, but that clearly indicate that someone is dealing with an illness that's part of a specific family of diagnoses.

An example of this is "Depressive Disorder NOS." A doctor using the DSM-IV to diagnose a patient may have chosen to label that person's diagnosis in this way because although it was clear her symptoms showed she was dealing with a particular type of depression (rather than, say, a panic disorder or an anxiety disorder), there wasn't enough information to home in a specific type of depression, such as dysthymia or bipolar disorder.

Why "NOS" Is No Longer Used in the DSM

In May 2013, the APA published an updated version of the DSM-IV. In the DSM-5 (note that the use of Roman numerals was dropped from the title of the manual), the authors decided to eliminate "not otherwise specified" and replace it (and "NOS") with "other specified" and "unspecified" to indicate clusters of symptoms that do not neatly fit into another existing category.

Why two terms to replace one? The difference is based on whether a diagnosing doctor chooses to indicate why the diagnostic criteria were not met. An example of "other specified" might be a depressive episode that does not have the full number of symptoms to meet the formal diagnosis.

By contrast, "unspecified" might be used in a situation in which there isn't enough information to make a more specific diagnosis. According to the APA, "unspecified" allows doctors to provide patients with the best possible care in, for example, emergency situations when there isn't time to get all the information necessary to make a solid diagnosis, but treatment is nevertheless needed. An "unspecified" label will allow a physician to be as specific as possible in his diagnosis without necessarily showing that a patient meets the full criteria for a given diagnosis.

Making Diagnoses More Universal

Replacing "NOS" brings the DSM-5 more in line with the World Health Organization's International Classification of Diseases (ICD). This diagnostic tool is "the foundation for the identification of health trends and statistics globally and the international standard for reporting diseases and health conditions.

It is the diagnostic classification standard for all clinical and research purposes," according to the World Health Organization's website. The ICD requires mandatory codes for disorders that do not precisely fit current definitions for major disorders.

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