Sleep onset insomnia, sleep maintaining insomnia and insomnia with early morning awakening--temporal stability of subtypes in a longitudinal study on general practice attenders.

The present study investigated the temporal stability of insomnia patterns during a 4-month study period, classifying insomnia as sleep-onset insomnia, sleep-maintaining insomnia or insomnia with early morning awakening. In a longitudinal study design, 2,512 general practice attenders were investigated at the time of the first inquiry (T1) with a questionnaire. Four months later (T2), all patients complaining of difficulties in initiating and/or maintaining sleep and/or early morning awakening (n = 328) were again contacted by mail and received the same questionnaire as at T1. According to the reported symptoms, patients were assigned to the different subtypes of insomnia. The diagnosis at T1 was then compared with the diagnosis at T2 4 months later. Only about half of all patients who complained of difficulties in initiating sleep at T1 still exclusively reported sleep-onset insomnia 4 months later, whereas the remaining patients were distributed to different subtypes. The stability of sleep-maintaining insomnia and insomnia with early morning awakening was even lower. Comorbidity with a somatic or psychiatric disorder at T1 and change in hypnotic treatment did not account for the instability of the respective subgroup of insomnia. These findings illustrate that cross-sectional studies focusing on subtypes of insomnia, e.g. sleep-onset insomnia, may lead to erroneous results.