Diurnal salivary cortisol concentrations in Parkinson’s disease: increased total secretion and morning cortisol concentrations

BACKGROUND Parkinson's disease (PD) is a chronic neurodegenerative disorder. There is limited knowledge about the function of the hypothalamic-pituitary-adrenal axis in PD. The primary aim of this prospective study was to analyze diurnal salivary cortisol concentrations in patients with PD and correlate these with age, gender, body mass index (BMI), duration of PD, and pain. The secondary aim was to compare the results with a healthy reference group. METHODS Fifty-nine PD patients, 35 women and 24 men, aged 50-79 years, were recruited. The reference group comprised healthy individuals matched for age, gender, BMI, and time point for sampling. Salivary cortisol was collected at 8 am, 1 pm, and 8 pm, and 8 am the next day using cotton-based Salivette(®) tubes and analyzed using Spectria(®) Cortisol I(125). A visual analog scale was used for estimation of pain. RESULTS The median cortisol concentration was 16.0 (5.8-30.2) nmol/L at 8 am, 5.8 (3.0-16.4) at 1 pm, 2.8 (1.6-8.0) at 8 pm, and 14.0 (7.5-28.7) at 8 am the next day. Total secretion and rate of cortisol secretion during the day (8 am-8 pm) and the concentration of cortisol on the next morning were lower (12.5 nmol/L) in the reference group. No significant correlations with age, gender, BMI, duration of PD, Hoehn and Yahr score, Unified Parkinson's Disease Rating Scale III score, gait, pain, or cortisol concentrations were found. CONCLUSION The neurodegenerative changes in PD does not seem to interfere with the hypothalamic-pituitary-adrenal axis. Salivary cortisol concentrations in PD patients were increased in the morning compared with the reference group, and were not influenced by motor dysfunction, duration of disease, or coexistence of chronic or acute pain.