...depression.

This is related to something they make medical students memorize. When someone comes in with hypertension, it is always good to check whether the person has renal artery stenosis because this is one of the few causes of hypertension we can actually fix. Renal artery stenosis results in hypertension because your kidneys secrete hormones that are involved in maintaining your blood pressure. How much hormones they decide to secrete is determined largely by the blood pressure that is felt by your kidneys; thus, when you block blood flow to the kidneys, they become convinced that you are hypotensive and pump out more hormones. The effect of the hormones is to make you hypertensive. Remove the stenosis of the blood vessel, and the hypertension goes away. (The hormone is incidentally called renin. More about renal stenosis here.)

Well it turns out that there is a brain analogue to this disease: depression caused by carotid hypertension. This study showed that stenting and opening the carotid relieved the depression in some patients:

Inserting a stent to open a narrowed carotid artery has been found to reduce symptoms of depression that may be associated with carotid stenosis, according to a study in the August issue of Radiology.

"The patients in this study who received carotid stenting showed significantly fewer depressive symptoms than those who did not," said the study's lead author Wolfgang Mlekusch, M.D., specialist of clinical angiology and internal medicine at Vienna General Hospital and Medical School in Vienna, Austria.

Carotid stenosis is caused by the formation of plaque within the carotid artery, which supplies blood to the brain. The build-up of plaque narrows the opening in the artery and can lead to stroke. Until recently, surgery was the standard treatment for this disease, but carotid stenting has emerged as an accepted minimally invasive alternative to restore blood flow to the brain. To perform the procedure, an interventional radiologist uses an image-guidance system such as computed tomography and a guide wire to reach the site of the narrowing in the artery, expands the artery with a balloon and inserts a stent to hold the artery open.

According to the National Center for Health Statistics, cerebrovascular disease is the third leading cause of death in the United States. Recent studies have shown that some depressive disorders may be caused by cerebrovascular diseases such as carotid stenosis, which restrict blood flow to the brain. These disorders are collectively known as "vascular depression."

Dr. Mlekusch and colleagues studied 143 patients with carotid stenosis and 102 age- and gender-matched controls with peripheral artery disease (PAD) scheduled to undergo lower-limb angioplasty, a surgical procedure. All patients were tested for depressive symptoms based on the Beck Depression Inventory (BDI). BDI scores of 10 or above indicate substantial depressive symptoms.

Patients with a high level of carotid stenosis (greater than 80 percent) more frequently exhibited substantial depressive symptoms compared to controls. Forty-eight (33.6 percent) of the patients with carotid stenosis presented with depressive symptoms, compared with 17 (16.7 percent) of the control patients.

Four weeks after carotid stenting, the BDI questionnaire was administered again. This time only 9.8 percent of the patients with carotid stenosis exhibited depressive symptoms compared with 13 percent of the patients who had undergone angioplasty.

I can't imagine that this is the most common form of depression, so I wouldn't recommend this for everyone. However, the reason that we memorize renal stenosis is because it is a form of hypertension where you can actually do something about it. In an elderly patient where carotid stenosis is likely, maybe it would be good to check for it as the underlying cause of depression.