Spectrum disorder

A spectrum disorder is a mental disorder that includes a range of linked conditions, sometimes also extending to include singular symptoms and traits. The different elements of a spectrum either have a similar appearance or are thought to be caused by the same underlying mechanism. In either case, a spectrum approach is taken because there appears to be "not a unitary disorder but rather a syndrome composed of subgroups". The spectrum may represent a range of severity, comprising relatively "severe" mental disorders through to relatively "mild and nonclinical deficits". In some cases, a spectrum approach joins conditions that were previously considered separately. A notable example of this trend is the autism spectrum, where conditions on this spectrum may now all be referred to as autism spectrum disorders. A spectrum approach may also expand the type or the severity of issues which are included, which may lessen the gap with other diagnoses or with what is considered "normal". Proponents of this approach argue that it is in line with evidence of gradations in the type or severity of symptoms in the general population. The term spectrum was originally used in physics to indicate an apparent qualitative distinction arising from a quantitative continuum (i.e. a series of distinct colors experienced when a beam of white light is dispersed by a prism according to wavelength). Isaac Newton first used the word spectrum (Latin for "appearance" or "apparition") in print in 1671, in describing his experiments in optics. The term was first used by analogy in psychiatry with a slightly different connotation, to identify a group of conditions that is qualitatively distinct in appearance but believed to be related from an underlying pathogenic point of view. It has been noted that for clinicians trained after the publication of DSM-III (1980), the spectrum concept in psychiatry may be relatively new, but that it has a long and distinguished history that dates back to Emil Kraepelin and beyond.