by Jennifer Bolton and Serena Smith, TMS Clinicians at SeattleNTC
Alzheimer’s disease is the most common cause of dementia, a general term for the deterioration of brain function. At age 60, the risk of developing Alzheimer’s disease is 1 in every 100 people; this risk increases to 30-50 in every 100 people by the age 85. Alzheimer’s disease is characterized by the loss of memory, language, and judgment that noticeably interferes with occupational and social functioning. There is no known cure for Alzheimer’s disease, however therapies do exist to combat symptoms. Though the exact mechanism is unknown, one such potential therapeutic aid for Alzheimer’s disease and dementia is repetitive transcranial magnetic stimulation (rTMS), a noninvasive form of brain stimulation, administered over the dorsolateral prefrontal cortex (DLPFC). Circuits connecting the DLPFC to deeper areas of the brain, including the basal ganglia, have been shown through imaging studies to be important in many cognitive functions. Stimulating the DLPFC may reinforce these circuits, thereby improving their function.
In a study by Ahmed et al 45 patients diagnosed with Alzheimer’s disease were randomly assigned to receive three different rTMS treatments: bilateral high frequency rTMS (20 Hz), bilateral low frequency rTMS (1 Hz), and bilateral sham rTMS (simulation of rTMS without stimulating the brain).  rTMS was administered bilaterally over the DLPFC, and all patients received daily rTMS sessions for five days. The subjects were evaluated in terms of stages of dementia, activity levels, and depressive symptoms. Patients receiving bilateral high frequency rTMS tended to improve more than those in the other treatment groups across all rating scales. A statistically significant difference was found between the outcomes of the patients receiving high frequency rTMS and those patients in the sham and low frequency groups.
Additional analyses were performed after splitting subjects into two sub-groups based on the severity of dementia: mild/moderate dementia and severe dementia. Out of all of the patients receiving high frequency treatment the mild/moderate group significantly improved, whereas those in the severe group did not. Out of all patients receiving low frequency rTMS (1 Hz), there was significant improvement in daily activity scores in the mild/moderate group only. In this same group, there was no significant change in either dementia or depressive symptoms. The group of patients receiving sham treatment for Alzheimer’s disease did not significantly improve in any of the three categories.
This study supports that multiple bilateral high frequency (20 Hz) rTMS treatments administered over bilateral DLPFC of patients with mild/moderate dementia can lessen the severity of dementia and depression as well as improve activity levels. Although additional studies should be conducted to provide more evidence for this treatment, the data presented above indicates that rTMS may hold potential for the treatment of the early stages of Alzheimer’s disease.
 Burns A, Jacoby R, Levy R (1991) Neurological signs in Alzheimer’s disease. Aging 20:45–51.  Ahmed MA, Darwish ES, Khedr EM, El serogy YM, Ali AM. (2012) Effects of Low versus high frequency of repetitive transcranial magnetic stimulation on cognitive function and cortical excitability in Alzheimer’s dementia. J Neurol 259:83-92.