CLINICAL FACTORS CONTRIBUTING TO THE DIFFERENTIAL-DIAGNOSIS OF PRIMARY INSOMNIA AND INSOMNIA RELATED TO MENTAL-DISORDERS

Objective: Primary insomnia and insomnia related to mental disorders a re the two most common DSM-IV insomnia diagnoses, but distinguishing b etween them is difficult in clinical practice. This analysis was perfo rmed to identify clinical factors used by sleep specialists to disting uish primary insomnia from insomnia related to mental disorders. Metho d: Clinicians evaluated 216 patients referred for insomnia at five cli nical sites, rated a list of clinical factors judged to contribute to each patient's presentation, and assigned diagnoses. Analysis of varia nce was performed, with contributing factors as the dependent variable and diagnostic group and clinic location as independent variables. Re sults: Sleep specialists rated a psychiatric disorder as a stronger fa ctor for insomnia related to mental disorders and rated negative condi tioning and sleep hygiene as stronger factors for primary insomnia. Ho wever, a psychiatric disorder was rated as a contributing factor for 7 7% of patients who received a first diagnosis of primary insomnia. Con clusions: While neither sleep hygiene nor negative conditioning is a d iagnostic criterion in DSM-IV, these results support the face validity of these clinical factors distinguishing between primary insomnia and insomnia related to mental disorders. The use of a psychiatric disord er as an inclusion criterion for insomnia related to mental disorders and an exclusion criterion for primary insomnia reinforces a categoric al distinction between the two diagnoses, but the contribution of psyc hiatric symptoms in primary insomnia appears to be a clinically releva nt one. These findings suggest the need for studies on the validity of negative conditioning and sleep hygiene in the etiology of primary in somnia, as well as on the significance of psychiatric disorders, espec ially depression, in primary insomnia.