Small vessel ischemia is a condition in which blood flow through small arteries and arterioles is restricted because of blockage or constriction of the vessels. Severe or prolonged ischemia can cause the tissue that is fed by the small vessels to die because of a lack of oxygen. The effects of small vessel ischemia are usually most notable in the brain, which develops white matter lesions (WML), decreased volume of white matter and lacunar infarcts. Ischemic disease of the small vessels can also cause damage to the heart and kidneys. Although the specific causes of small vessel ischemic disease are unknown, people who are elderly or who suffer from hypertension or diabetes mellitus have a higher risk of developing the disorder.

Ischemia occurs when an artery or arteriole becomes too narrow or obstructed. Arteriosclerosis, or hardening of the arteries, is caused by fatty deposits inside the vessels that cause its walls to become stiff and inflexible. The deposits, also called plaques, make the inside of the vessels more narrow, allowing less blood to pass through. The immune system regards the plaques as wounds and responds by producing chronic inflammation, which can lead to blood clots that block the vessels completely and cause tissue death in the affected organ. When this process occurs in small arteries and arterioles, it is called small vessel ischemia or small vessel ischemic disease.

Scientists have extensively researched arterial disease, but as of early 2011, it was still unclear why some people develop disease in the small vessels rather than in larger arteries. The scientific community has identified several possible risk factors for small vessel disease, however. Women develop small vessel ischemic disease more often than men, and estrogen deficiency increases a woman's chance of developing the disorder. Lifestyle factors such as a sedentary lifestyle, tobacco use and obesity are also risk factors. Diabetes mellitus, insulin resistance, hypertension and advanced age are also associated with small vessel ischemia.

Small vessel ischemia causes a characteristic pattern of damage in the brain. Gray matter, which consists mostly of the cell bodies of the brain's neurons, is principally fed by larger arteries. The brain's white matter, which is deeper in the brain and mostly made up of the myelinated axons of neurons, is fed by long, small arteries and arterioles. Therefore, small vessel disease causes WML; lacunar infarcts, which are small deep brain ischemic strokes; and a reduction of white matter volume that includes a loss of myelin. Multiple sclerosis also causes WML and loss of myelin, but through a different process than that of small vessel ischemia.

In the heart, small vessel ischemic disease causes symptoms such as chest pain or pressure, shortness of breath and fatigue. The symptoms are the same as those caused by disease of the heart's larger vessels but can occur even when the larger vessels are healthy. If standard cardiac tests such as an electrocardiogram or coronary angiogram do not show disease of the larger vessels, the physician might perform an endothelial dysfunction test to measure blood flow through the small vessels. Doctors treat small vessel ischemia in the heart with the same medications as large vessel ischemia, but surgery and stents are not options for treating small vessel disease.

Small vessel ischemic disease can also damage the kidneys. The glomuleri, structures within the nephrons of the kidneys that are involved with filtering blood to form urine, suffer damage as a result of small vessel disease. Kidney function is affected when the small vessels in the glomuleri develop plaques and endothelial dysfunction. People who have small vessel disease of the brain are very likely to also have small vessel ischemia of the kidneys, and because kidney dysfunction often goes undiagnosed, physicians should consider testing glomular filtration rate in patients who show WML and lacunar infarcts in the brain.

The vital organs can suffer lasting damage from small vessel ischemic disease. A healthy lifestyle that includes a low-fat diet, regular exercise, maintenance of a healthy weight and avoidance of tobacco goes a long way toward preventing this potentially serious disorder. Proper medical monitoring and treatment, along with any necessary lifestyle changes, can lessen organ damage for people who already suffer from small vessel ischemic disease.