'Subthreshold' mental disorders: A review and synthesis of studies on minor depression and other 'brand names'

Background: Subthreshold conditions (i.e. not meeting full diagnostic criteria for mental disorders in DSM-IV or ICD-10) are prevalent and associated with significant costs and disability. Observed more in primary care and community populations than in specialty settings, varying conceptualisations have been applied to define these conditions. Aims: To examine definitional issues for subthreshold forms of depression (e.g. minor depression) and to suggest future directions for research and nosology in psychiatry and primary care. Method: A Medline search was conducted. The relevant articles were reviewed with regard to specific categories of information. Results: Studies applied a myriad of names and definitions for subthreshold depression with varying duration, symptom thresholds and exclusions. Prevalence rates also vary depending upon the definitions, settings and populations researched. Conclusions: Future research needs to apply methodological and intellectual rigour and systematically consider a broader clinical and nosological context. In addition, collaboration between psychiatry and primary care on research and clinical issues is needed.