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 patt erns during a 4-month study period, classifying insomnia as sleep-onse t insomnia, sleep-maintaining insomnia or insomnia with early morning awakening. In a longitudinal study design, 2,512 general practice atte nders were investigated at the time of the first inquiry (T1) with a q uestionnaire. Four months later (T2), all patients complaining of diff iculties 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 abo ut half of all patients who complained of difficulties in initiating s leep at T1 still exclusively reported sleep-onset insomnia 4 months la ter, whereas the remaining patients were distributed to different subt ypes. The stability of sleep-maintaining insomnia and insomnia with ea rly morning awakening was even lower. Comorbidity with a somatic or ps ychiatric disorder at T1 and change in hypnotic treatment did not acco unt 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.