Subthreshold affective disorders: a useful concept in psychiatric epidemiology?

In recent years an extensive literature has grown up around the concepts of subthreshold, subsyndromal, minor and brief recurrent affective disorder and their applications in population-based research. The aim of this short review is to examine the definitions and current status of these proposed categories with special reference to depression, and to assess their potential contribution to psychiatric epidemiology.

A Medline search was carried out for the period 1965-1999, based on the above four terms. Relevant references found in all identified publications were also followed up.

In great measure these constructs have been developed as a response to deficiencies in the DSM classification system and to a lesser extent in the ICD. The groups are all defined by having fewer criterial symptoms, or a shorter duration of symptoms, than the 'official' diagnostic categories. Use of these definitions has resulted in widely varying prevalence estimates.

Improved methods are badly needed for classifying all those persons in the wider community who are in need of medical treatment and help for psychological disorder, but do not satisfy operational criteria laid down in the official guidelines. This cannot, however, be achieved simply by lowering operational thresholds in these systems. Further research on clinical and psycho-social characteristics of the common mental disorders is called for, and in many societies a favourable setting is that of primary health care, where a move towards pragmatic, comprehensive classification of community health problems is already under way.