Around the time transcranial magnetic stimulation (TMS) was approved by the FDA in 2008, a few studies published findings concerning which individual patient characteristics might be associated with a robust antidepressant response to TMS. One such study (Fregni et al.) found that age was a statistically significant variable; that TMS produces a greater antidepressant effect in younger patients compared to older patients. However, this is not to say that TMS is ineffective in geriatric depression. Quite the reverse. Older adults with depression stand to benefit greatly from TMS.
As a non-invasive procedure with a high degree of tolerability, one of the advantages of TMS is its safety profile. Side effects are relatively infrequent and when they do occur, they are typically mild. (Common side effects reported are scalp discomfort at the site of stimulation, headache, and twitching of facial muscles.) In treating the elderly the gentle nature of TMS is especially important. Moreover, considering that the magnetic stimulation is localized, namely, limited to a certain area of the body, TMS can be quite forgiving for patients who are physically frail and/or taking multiple medications.
Turning now to the efficacy of TMS in geriatric depression, by and large there is heterogeneity among results. While some studies (like the one mentioned above, by Fregni and colleagues) show that older age is associated with a poorer antidepressant response to TMS, other studies have failed to replicate these findings. In fact, a growing body of evidence suggests otherwise — that age is not a significant predictor of efficacy and that a similar treatment effect is observed among older and younger adults (e.g. see Jorge et al.). With older adults however, what is important to keep in mind are the physiological changes that come with the aging process and how these changes might influence efficacy.
In a review by Iriarte and George, age-related changes that underlie treatment efficacy are discussed. The authors point out that cerebral atrophy — loss of brain volume, be it from normal aging and/or disease — increases the distance between the scalp and cortex. How does this factor into TMS therapy? Well, it should be noted that the intensity of the magnetic pulses decreases with an increase in distance from the coil. The challenge then becomes delivering pulses of optimal intensity to the region of the brain that is of interest — specifically the left dorsolateral prefrontal cortex. To correct for this, researchers adjusted the treatment parameters and found that a stimulation intensity of 120% is most effective and, as of now, this is the standard used in practice. As further noted in the review, more treatment sessions (i.e. a greater number of pulses) are associated with higher efficacy in geriatric depression. Older patients, in other words, tend to benefit from more days of treatment.
While major depressive disorder is the only FDA-approved indication for TMS therapy, researchers have observed many ancillary benefits. Some benefits described, which are applicable to geriatric patients, consist of reducing nicotine craving and improving cognitive performance such as memory and concentration. Considering the prevalence of cognitive impairment among the elderly the ability to modulate cognitive function would prove invaluable. It is important to keep in mind however, that this research is preliminary, for the improvements in cognition might be due, at least in part, to improvements in mood. Hence, additional studies are needed.
