Objective: Insomnia could be a symptom of underlying psychiatric or physical disorder, a risk factor for other psychiatric disorder, or a discrete psychiatric disorder per se. In order to determine the nosological status of primary insomnia, an outcome study was carried out to investigate its diagnostic stability and its relationship to subsequent psychiatric disorders.
Methods: Fifty-three primary insomnia patients in a university hospital psychiatric outpatient clinic were assessed by retrospective case note review, followed by a 6 month prospective follow up with Structured Clinical Interview Schedule for DSM-IV In-patient (SCID-I/P, version 2.0, and a sleep questionnaire.
Results: The majority of patients (n =44, 83%) did not develop other psychiatric disorders after 13.4+/-1.2 years from the onset of insomnia. Nine patients (17%) developed mood disorder (n =6), anxiety disorder (n =2) and somatoform disorder (n =1) at 6.3+/-2.3 years after the onset of insomnia. Subjective deterioration of insomnia and a shorter duration of sleep symptoms at the first consultation were associated with the development of secondary psychiatric disorders. Approximately one-third (n =17, 32%) reported symptoms improvement and six (13.2%) were free from medications. Better education was the only factor that predicted improvement in symptoms.
Conclusions: There existed a longitudinal diagnostic stability of primary insomnia in a majority of clinical patients. However, in a proportion of patients, it might either be a risk factor or a prodrome of mood or anxiety disorders.