RESUMEN
BACKGROUND: Circadian dysfunction is thought to take part in the pathogenesis of sleep disorders in Alzheimer's disease (AD) and in AD pathophysiology itself. OBJECTIVE: Our study aims to calculate dim light melatonin onset (DLMO) secretion in order to define the circadian phase in patients with AD at an early stage of the disease. METHODS: Twenty-one patients (M/F: 11/10; mean age 74.1 ± 5.4 years; mean disease duration 3.4 ± 1.6 years) with a diagnosis of AD and 17 healthy controls (HC; M/F: 10/7; mean age 67.47 ± 3.8 years) were investigated for subjective nocturnal sleep quality and chronotype, for DLMO and quantitative aspects of the evening melatonin secretion by means of a 5-point in-home evening melatonin saliva test. RESULTS: Subjective sleep quality score on the Pittsburgh Sleep Quality Index questionnaire (PSQI) above 5 (p = 0.24), insomnia frequency as measured by Sleep Condition Indicator Questionnaire (p = 0.823) and the subjective chronotype according to Morning Evening Questionnaire (MEQ) scores distribution (p = 0.464) did not differ between AD and HC. However, DLMO occurred significantly later (55 min; p = 0.028), and melatonin secretion following DLMO was significantly decreased in AD patients compared to HC. CONCLUSION: Initial evening secretion of melatonin proves to be delayed and mildly impaired in patients with a mild/moderate form of Alzheimer disease while patients' subjective sleep parameters and chronotype are reported to be similar to those of HC. These results indicate that subclinical altered patterns of melatonin secretion occur in subjects with AD at an early stage of the disease.