PBMT for major depressive disorder
Major depressive disorder (MDD), also known as depression, is the most prevalent mental disorder with an estimated 322 million people with different degrees of MDD worldwide, according to a 2017 report by the World Health Organization. The recognized treatments for MDD include pharmacotherapy, psychotherapy, and physical therapy. However, nearly 30% of patients do not show adequate relief of symptoms after multiple drug trials. Furthermore, most MDD patients prefer non-pharmacological therapies when they are treatment-resistant or intolerant to antidepressants, whereas the effectiveness of psychotherapy is limited by multiple factors (i.e., environment, experiences of therapists, emotional shame of patients, etc.). Therefore, as a novel non-invasive and side-effect-free physical intervention method, NIR light transcranial PBMT was demonstrated to hold the promise of alternative or adjuvant treatment for MDD patients.
Moreover, the therapeutic effect of PBMT is related to the irradiation site, and the intervention results of PBMT on MDD at different irradiation sites have been observed. Disner et al. conducted an RCT of PBMT as an adjunctive treatment for major depression. They randomly assigned 51 patients to three groups (left, right prefrontal irradiation group and sham treatment group). The treatment effect was assessed using the Center for Epidemiologic Studies Depression Scale (CESD) after 2 weeks of treatment. They found that the depressive symptoms of patients who received right prefrontal irradiation were significantly improved, while there was no obvious improvement in the symptoms of patients who received left prefrontal irradiation or sham treatment. They speculated that the reason was that depression was more strongly related to the activity of the right prefrontal cortex. Therefore, when conducting PBMT, the irradiation site should be reasonably selected, which can help to achieve precise treatment. The above-mentioned RCT suggested that the illumination sites should be set on the right forehead when using PBMT to treat MDD.
PBMT for Alzheimer's disease
Alzheimer's disease (AD) is a chronic neurodegenerative disease and the most common form of dementia (Alzheimer's disease accounts for approximately 60%–70% of all dementia patients). The main clinical manifestations of AD are cognitive, executive and memory dysfunction in the brain, characterized pathologically by abnormal deposition of β-amyloid (Aβ) and plaques formed with hyperphosphorylated tau protein, which results in neurofibrillary tangles, triggers neuronal damage, apoptosis, neuroinflammation, and brain function disorders in AD patients. The number of patients with AD and related dementias in China has exceeded 15 million in 2020,35 accounting for a quarter of the world. In addition, AD has been ranked 15th in the list of diseases with the highest number of deaths in China. With the increasing aging of the population, the impact of AD on the daily life of the population is becoming increasingly severe. However, the existing therapeutic drugs are unable to reverse the progression of AD patients, and thus there is an urgent need to develop new drugs or alternative treatments.
Recent clinical studies have shown that PBMT can alleviate the AD symptoms and improve the memory and self-care abilities of the patients. In 2017, Saltmarche et al. conducted a PBMT which combined transcranial and transnasal irradiation (for 12 weeks, 20 min per day, using NIR light at a wavelength of 810 nm) in five AD patients with mild to severe cognitive impairment. They observed significant improvements in the mental status of the patients in the following 4 weeks and found the recovery of brain function in all five subjects, accompanied by better sleep quality, lower frequency of angry feelings and anxiety. Besides, no side effects of PBMT were detected. In 2019, Chao tested the efficacy of transcranial and transnasal PBMT home care in eight patients with dementia with a mean age of 80 years. He found that after 12 weeks of treatment, four patients receiving PBMT had their mean scores on the Alzheimer's Disease Assessment Scale-Cognitive Subscale (a scale used to assess cognitive ability in patients with AD, with lower scores indicating better cognitive performance) decreased by 13.9%, while the mean score in the conventional treatment group increased by 22.1%. In this study, PBMT was found to enhance cerebral perfusion and increase connectivity between the posterior cingulate cortex and the lateral parietal nodes by arterial spin-labeled perfusion magnetic resonance imaging. This experiment showed that at-home PBMT has sufficient efficacy in improving cognitive performance in AD patients and is a promising new home physiotherapy method.
