Parkinson's disease. PD is the second most common neurodegenerative disorder after Alzheimer's disease and affects more than 1% of the elderly population worldwide. Aarsland Påhlhagen Ballard Ehrt Svenningsson 2012. PD is a neuropsychiatric disorder characterized by the cardinal signs of rigidity bradykinesia and tremor. Although motor features define the disorder various non-motor features are typically seen including sleep disturbances, anxiety, and depression. Recent studies have proposed that non-motor complications often carry a greater impact than motor features in PD their recognition is often the key to the successful treatment of a Parkinson patient Simuni Sethi 2008. The core of PD management is symptomatic treatment with drugs, however, long term treatment of this array of symptoms with various drugs causes the occurrence of adverse short and long term side effects such as dyskinesia and psychosis Kalia Lang 2015. These side effects reflect the importance of implementing non-invasive treatments to reduce the total daily dose of dopamine replacement Willis Moore Armstrong 2012. On this basis, bright light therapy BLT has been proposed as the treatment of choice for seasonal affective disorder and was also shown to be effective in the improvement of depression, anxiety, insomnia and the motor symptoms associated with PD Willis Turner 2007. Despite the established therapeutic potential of BLT in seasonal depression and potential usefulness across a wide array of applications considerably less is known about the efficacy of BLT in treating both non-motor and motor symptoms in more advanced patients the side effects and tolerability of BLT in populations with PD. Thus this may restrict the depth of understanding of the efficacy of BLT in patients with PD.
The timing of BLT. The timing when BLT was administered is an important condition to understand as studies have suggested that both the morning light and evening light are beneficial to PD patients. Even Schröder Friedman Rouillon 2008 Lack Wright 2007 Rutten et al 2016 have proposed that patients with PD have a phase advance circadian rhythm hence evening light might be more effective in treating not only insomnia but also depressive symptoms in this population. Evening exposure tends to lead to greater alertness in the evening and a tendency towards falling asleep later at night and awakening later in the morning McClung 2007. Hence bright light exposure in the evening can cause a phase delay in the circadian rhythm of melatonin onset. However, Paus et al 2007 have determined that morning light can improve mood and sleep in PD patients as well It has been argued that exposure to bright light early in the day will phase advance the circadian rhythm. This will lead an individual to be more alert in the earlier hours of the day and to shift the timing of sleep onset to earlier in the evening Weber Killgore 2013. Furthermore, PD affects individuals differently some individuals may not experience all the symptoms associated with PD and the symptoms may vary in their severity between patients Burke Albin 2011. Thus Terman Terman and Ross 1998 proposed that the time of administration of BLT should be dependent on the nature of the patient’s complaints and chronotype. Willis 2015 had stated that PD is a progressive neurodegenerative disorder that results in a gradual worsening of both motor and nonmotor symptoms hence the positive results obtained through the studies have shown that patients did benefit from the treatment over a four year period. However, this seminar did not mention the side effects of BLT that may contribute to polypharmacy. Polypharmacy is the use of excess numbers of medications which increases the risk for adverse drug reactions Alpert 2017.
Studies on the side effects of BLT on mood disordered individuals have proposed that the side effects range from minor to severe Brouwer et al 2017. The minor side effects were categorized into two subgroups complaints of vision and ocular discomfort. Studies have reported complaints of vision such as seeing flashing lights on spots and glare difficulty seeing in the presence of very bright light Müller Seifritz Hatzinger Hemmeter Holsboer Trachsler 1997. While the majority of complaints can be classified as ocular discomfort which can be explained by asthenopia, the combination of non-specific symptoms such as eye discomfort and burning Ozkan Arik 1994. Furthermore, studies on the acute side effects of BLT have shown that mood disordered individuals are known to exhibit increased attentional vigilance for negative information, an increased propensity to interpret physiological changes as the aversive and increased sensation of anticipatory pain Botanov Ilardi 2013. Such depressive interpretive biases could conceivably lead to the over-reporting of adverse effects while undergoing BLT. Thus these side effects might also be reflected in PD patients which may cause polypharmacy and lead to increased severity of PD. In conclusion since the current treatment options for the motor and non-motor symptoms associated with PD can have serious side effects alternative non-invasive treatment like BLT would be advantageous. The studies on the effects of BLT proposed in the seminar by Willis 2015 had shown to be an effective treatment for motor and non-motor symptoms in the general population of PD. This justifies the important role that psychologists have in providing a better quality of life to these patients. However, due to the critiques mentioned precautions should be taken when considering the validity and reliability of the findings. Hence more theoretical supports need to be built and more empirical studies must be conducted to include factors that will be crucial to understand the conditions to which BLT will be most beneficial to PD patients. If future studies provide consistent positive effects of BLT on patients with PD then more efficacious treatment regimens that precipitate fewer aversive side effects may be anticipated. Consequently, future studies will also provide a new perspective from which a better understanding of the etiology of this neuropsychiatric disease may be derived.
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