Spectrum disorder

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A spectrum disorder in psychiatry is a mental disorder thought to be "not a unitary disorder but rather a syndrome composed of subgroups".^[1]

The term spectrum was originally used in physics to indicate an apparent qualitative distinction arising from a quantitative continuum (i.e. a series of colors formed when a beam of white light is dispersed by a prism so that their parts are arranged in the order of their wavelengths). In psychiatry, the concept of spectrum was first used with a slightly different connotation to identify a group of disorders that is qualitatively distinct in appearance (e.g. depression and alcoholism) but believed to be related from a pathogenic point of view. For different investigators, the hypothetical common pathogenic link has been of a different nature.^[1]

Spectrum, dimension and continuum are related concepts. Some use them interchangeably while some argue the fine points of difference. The term continuum suggests a simple straight line from severe to mild, while the term spectrum is used to indicate the fact that although there is a common denominator, a given type of individual may present with a given pattern of symptoms, reminiscent of the spectrum of distinct colors after refraction of light by a prism.^[1]

In general, a spectrum approach is contrasted with a categorical approach, which is most associated with the DSM and ICD schemes. A spectrum approach may start with the nuclear, classic DSM diagnostic criteria for a disorder and then include an additional broad range of issues including temperaments or traits, lifestyle, behavioural patterns, and personality characteristics.^[1]

It has been noted that for clinicians trained after the publication of DSM-III, the spectrum concept may be relatively new, but that it has a long and distinguished history that dates back to Emil Kraepelin and beyond. It has been argued that within the data used as the basis for the DSM is a large literature leading to an alternative conclusion that a spectrum classification provides a better perspective on phenomenology of psychopathology than a categorical classification.^[1]

The widely-used DSM and ICD manuals are generally limited to categorical diagnoses but do recognize some subsyndromal subtypes: schizotypal personality disorder, dysthymia and cyclothymia.

Some additional proposed spectra include a bipolar spectrum, a schizophrenia spectrum, an autism spectrum, a post-traumatic stress spectrum, an obsessive-compulsive spectrum, a social anxiety spectrum, and a panic-agoraphobia spectrum. Other higher-level spectra are often proposed, which categorize disorders into even fewer overarching spectra. Different spectrum theories for a given disorder may also user different terminology. For example various spectrum concepts of depression have been called the depression spectrum, the affective spectrum, and the mood spectrum.^[1]

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