Transcranial bright light treatment via the ear canals in seasonal affective disorder: A randomized, Double-blind dose-response study

Abstract

Background: Bright light treatment is effective for seasonal affective disorder (SAD), although the mechanisms ofaction are still unknown. We investigated whether transcranial bright light via the ear canals has an antidepressanteffect in the treatment of SAD.Methods: During the four-week study period, 89 patients (67 females; 22 males, aged 22-65, mean ± SD age:43.2 ± 10.9 years) suffering from SAD were randomized to receive a 12-min daily dose of photic energy of one ofthree intensities (1 lumen/0.72 mW/cm2; 4 lumens/2.881 mW/cm2; 9 lumens/6.482 mW/cm2) via the ear canals.The light was produced using light-emitting diodes. The severity of depressive symptoms was assessed with theHamilton Depression Rating Scale - Seasonal Affective Disorder (SIGH-SAD), the Hamilton Anxiety Rating Scale(HAMA), and the Beck Depression Inventory (BDI). Cognitive performance was measured by the Trail Making Test(TMT). The within-group and between-group changes in these variables throughout the study were analysed witha repeated measures analysis of variance (ANOVA), whereas gender differences at baseline within the light groupswere analysed using Student's t-tests.Results: Patients in all three groups showed significant decreases in their BDI, HAMA, and SIGH-SAD scores. Responserates, i.e., an at least 50% decrease of symptoms as measured by the BDI, were 74%-79% in the three treatment groups.Corresponding variations for the SIGH-SAD and the HAMA were 35-45% and 47-62%, respectively. No intensity-baseddose-response relationships in the improvement of anxiety and depressive symptoms or cognitive performancebetween treatment groups were observed. Approximately one in four patients experienced mild adverse effects,of which the most common were headache, insomnia, and nausea.Conclusions: These results suggests that transcranial bright light treatment may have antidepressant and anxiolyticeffect in SAD patients, as both self- and psychiatrist-rated depressive and anxiety symptoms decreased in all treatmentgroups. These improvements are comparable to findings of earlier bright light studies that used conventional devices.The lack of dose response may be due to a saturation effect above a certain light intensity threshold. Further studieson the effects of transcranial bright light with an adequate placebo condition are needed.Trial registration: NCT01293409, ClinicalTrials.gov.