Bipolar disorder spectrum

Overview
The Bipolar spectrum refers to a category of mood disorders that feature abnormally elevated mood. These disorders range from Bipolar I disorder, featuring full-blown manic episodes, to cyclothymia, featuring less prominent hypomanic episodes. These disorders may also present with depressive symptoms or episodes that alternate with the elevated mood states, or with mixed episodes that feature symptoms of both. The concept of the Bipolar spectrum is similar to that of Emil Kraepelin's original concept of Manic depressive illness.

Referential nomenclature
A simple nomenclature system was introduced in 1978 by Angst, J., et al, to classify more easily individuals' affectedness within the spectrum, following a clinical study by the Psychiatric University Clinic of Zürich.

Points on the spectrum using this nomenclature are denoted using the following codes:
 * 'M' severe mania
 * 'D' severe depression (unipolar depression)
 * 'm' less severe mania (hypomania)
 * 'd' less severe depression

Thus, 'mD' represents a case with hypomania and major depression. A further distinction is sometimes made in the ordering of the letters, to represent the order of the episodes, where the patient's normal state is euthymic, interrupted by episodes of mania followed by depression ('MD') or vice versa ('DM').

Employing this schema, major depression would be denoted 'D'. Unipolar mania ('M') is, depending on the authority cited, either very rare, or nonexistent with such cases actually being 'Md'.

Unipolar hypomania ('m') without accompanying depression is not noted in the medical literature. There is speculation as to whether this condition may exist in the general population, but successful social functioning may define these high-achieving normals, rather than individuals suffering any substantial dysregulation.