As if pain and impaired mobility are not enough, multiple sclerosis (MS) patients are also plagued by another comorbidity – depression. It is estimated that people with MS have up to 50% lifetime risk for developing depressive symptoms. However, very little is known about the causes and influencing factors of MS-related depression. In a way, this type of depression is quite puzzling. It can occur at any stage of the disease and is not related to the severity of the symptoms. Scientists think that depression in MS patients is not simply a normal reaction to the debilitating symptoms but has a neurological reason.
According to lead author Dr. Stefan Gold
“Depression is one of the most common symptoms in patients with multiple sclerosis. It impacts cognitive function, quality of life, work performance and treatment compliance. Worst of all, it’s also one of the strongest predictors of suicide.”
Thus, researchers at the University of California at Los Angeles (UCLA) decided to investigate the cause(s) of MS-linked depression. Their hypothesis is that it is not a simply psychological problem but rather due to structural changes in the brain, i.e. “atrophy of a specific region of the hippocampus, a critical part of the brain involved in mood and memory, among other functions.”
The researchers used high-resolution magnetic resonance imaging (MRI) to study the MS brain and found three key sub-regions of the hippocampus that were smaller in people with MS when compared to those without MS. This observed atrophy was also linked to the hyperactivity of three interacting glands of the hypothalamic-pituitary-adrenal (HPA) axis. This axis plays a role in the regulation of reactions to stress other physiological processes. In depressed MS patients, the HPA axis released excessive amounts of the stress hormone cortisol. The researchers believe that this hyperactivity results in dysregulation and atrophy of the hippocampus that leads to the development of depressive symptoms.
The researchers found similarities between MS-linked depression and depression in people without MS but these should be further investigated in future studies.
According to co-author Dr. Nancy Sicotte
“Interestingly, this idea of a link between excessive activity of the HPA axis and reduced brain volume in the hippocampus hasn’t received a lot of attention, despite the fact that the most consistently reproduced findings in psychiatric patients with depression (but without MS) include hyperactivity of the HPA axis and smaller volumes of the hippocampus….So the next step is to compare MS patients with depression to psychiatric patients with depression to see how the disease progresses in each.”