Efficacy and Safety of Light Therapy for Parkinson Disease
Parkinson disease (PD) is the second most common neurodegenerative disorder, significantly impacting the quality of life (QoL) of affected individuals. It affects approximately 2% to 3% of the population aged 65 years and older. While PD is primarily characterized by motor symptoms such as asymmetric tremor, bradykinesia, and rigidity, it is also associated with a range of non-motor symptoms, including cognitive impairment, depression, sensory abnormalities, autonomic dysfunction, and sleep disturbances. The complexity of PD makes it a challenging condition to treat, and there are currently no effective therapies to prevent or halt its progression.
In recent years, light therapy (LT) has emerged as a potential treatment for various disorders, including circadian misalignment, seasonal and non-seasonal depression, sleep disorders, mood disorders, and cognitive dysfunction. LT involves exposure to artificial light, typically delivered via a light box or similar device. The therapeutic parameters of LT include wavelength, total daily exposure time, intensity, and timing of exposure during the day. Given its potential benefits, LT has been explored as a treatment for both motor and non-motor symptoms of PD.
This article presents a systematic review and meta-analysis of randomized controlled trials (RCTs) investigating the efficacy and safety of LT for PD. The review aims to critically evaluate the effects of LT on PD symptoms, including motor function, depression, sleep quality, daytime sleepiness, fatigue, and QoL. Additionally, the safety profile of LT is assessed by examining the incidence of adverse events reported in the included studies.
The systematic review and meta-analysis were conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The study was registered with the International Prospective Register of Systematic Reviews (No. CRD42020170794). A comprehensive search of the literature was performed using multiple databases, including Embase, PubMed, Cochrane, Web of Knowledge, ClinicalTrials.gov, Chinese National Knowledge Infrastructure, and Wanfang databases. The search covered studies published up to May 22, 2021. In addition to electronic searches, manual cross-referencing of bibliographies from relevant articles was conducted.
Studies were included in the review if they met the following criteria: (1) participants were diagnosed with idiopathic PD according to the UK Parkinson Disease Society Brain Bank Criteria or the Movement Disorders Society (MDS) diagnostic criteria; (2) the study involved a specific light intervention; (3) the study design was a randomized controlled trial with a control condition; and (4) the study reported outcome measures related to PD symptoms. Studies were excluded if the intervention combined LT with another treatment or if participants had comorbidities as the primary diagnosis of interest. The risk of bias in individual studies was assessed using the Cochrane Collaboration Risk of Bias tool.
A total of 12 full-text articles were identified as potentially eligible for inclusion. After screening and removing duplicates, six studies met the eligibility criteria and were included in the meta-analysis. The main characteristics of these studies, including sample size, intervention details, and outcome measures, were systematically extracted.
The meta-analysis focused on several key outcomes, including motor symptoms, depression, sleep quality, daytime sleepiness, fatigue, and QoL. Motor symptoms were assessed using the Unified Parkinson Disease Rating Scale (UPDRS) III in three studies and the MDS UPDRS III in two studies. The pooled results from these studies indicated that LT did not significantly improve clinician-rated motor function compared to control conditions (standardized mean difference [SMD] = -0.12; 95% confidence interval [CI], -0.41 to 0.16; P = 0.390).
Depression was evaluated in five studies using various depression rating scales. The meta-analysis revealed no significant reduction in depression scores with LT compared to control groups (SMD = -0.11; 95% CI, -0.40 to 0.17; P = 0.440). Subjective sleep quality was assessed in two studies, and the results showed a medium effect size favoring LT over control conditions (SMD = 0.46; 95% CI, 0.06 to 0.85; P = 0.020). Daytime sleepiness was evaluated in five studies, primarily using the Epworth Sleepiness Scale (ESS). The pooled analysis indicated no significant improvement in daytime sleepiness (SMD = -0.19; 95% CI, -0.47 to 0.10; P = 0.200). However, when analyzing only participants with ESS scores > 10 (indicating more severe symptoms), LT showed a significant improvement in daytime sleepiness compared to controls (mean difference [MD] = -1.81; 95% CI, -3.37 to -0.25; P = 0.020).
Fatigue was assessed in two studies, and the meta-analysis found no significant improvement with LT compared to control groups (SMD = -0.15; 95% CI, -0.64 to 0.35; P = 0.560). QoL was evaluated in three studies, and the pooled results indicated no significant difference between LT and control conditions (SMD = 0.07; 95% CI, -0.29 to 0.42; P = 0.710).
Data on adverse effects were available for all included trials. The pooled odds ratio (OR) for adverse events was 2.27 (95% CI, 1.02 to 5.06; P = 0.044), indicating a higher incidence of adverse events in the LT groups compared to control groups. The reported adverse events included eyestrain, itchy eyes, headache, gastrointestinal complaints, and general malaise. However, these adverse effects were generally mild and transient.
The findings of this systematic review and meta-analysis suggest that LT may have specific benefits for PD patients with severe daytime sleepiness (ESS > 10) and may improve subjective sleep quality. However, the evidence is limited by the small number of studies and the lack of long-term data on the effects of LT. The review highlights the need for larger, multi-center RCTs to further explore the potential benefits and safety of LT in the management of PD.
In conclusion, LT represents a novel and potentially valuable treatment option for certain symptoms of PD, particularly severe daytime sleepiness and sleep disturbances. While the incidence of adverse effects is higher with LT, these effects are generally mild and transient, making LT a safe treatment option for PD patients. Further research is needed to confirm these findings and to explore the potential benefits of LT for other symptoms of PD, including autonomic dysfunction, sensory abnormalities, and cognitive and neurobehavioral issues.
doi.org/10.1097/CM9.0000000000001818
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