Conway McLean, DPM, Journal columnist

Most Americans know at least a little about diabetes. After all, an increasing number of us are afflicted with the disease so a large percentage of the population has had some interaction. It’s hard to avoid learning something about it. Diabetes mellitus, the official name of this ubiquitous condition, is a complex metabolic disease that can have devastating effects on multiple organs in the body. The deleterious effects of diabetes on the eye, the kidneys, and the heart, are widely acknowledged and well-studied.

Regular readers of this column have learned of the reduction in (arterial) blood flow, as well as the challenges in fighting infection for those with this disease. Not discussed sufficiently in the media are the nerve changes. These lead to a variety of problems, maybe most dramatic are the infections and amputations resulting from a loss of “protective sensation,” a term referring to a reduced ability to feel certain types of pain. This is a key event in the development of most diabetic ulcers and the subsequent infections which lead to hospitalization and amputation.

Obviously, the nervous system is complex, perhaps the understatement of the year. Its functions are innumerable and include the obvious, the ability to feel pain. Also important, they allow us to control our skeletal muscles thereby allowing us to stand, walk and, most importantly, grab our cup of coffee. Nerves govern many automatic functions, like the oil glands near the surface which are necessary to keep skin healthy, as well as the minor job of heart contraction. These automatic functions, appropriately referred to as the autonomic nervous system, also work the arteries in our arms and legs, increasing flow when our muscles are exercising.

When the conversation turns to nerve function, you can’t ignore the human brain, the extraordinarily complex arrangement of nerves which enable us to think, to ponder, to calculate. This vital organ has multiple jobs, completing numerous tasks, many simultaneously. Our understanding of the brain (as well as the mind) is limited, but advances are made daily into this complex neural machine that is our brain.

Physicians who regularly care for people with diabetes often relate a common experience: these can be difficult patients, unwilling or unable to follow instructions, to care for themselves as directed. It’s a common topic of conversation, the typical dialogue running something like “my patient, Mr. Smith, just won’t follow instructions, even though it seems like he understands.” A similar discussion occurs in clinics and offices across the country.

The disease that is diabetes, in which the amount of glucose in the bloodstream is too high, acting as a poison and so altering multiple processes necessary for our continued existence, apparently makes people with diabetes unable to follow instructions and provide self-care as directed. Is it simply the stress of dealing with this challenging disease that makes people non-compliant? Apparently, just as diabetes causes nerve damage to the eyes and feet, it also affects the brain. But science has only recently begun to examine the effects of diabetes on thinking abilities, scientifically referred to as cognitive function.

Some scientists believe that by damaging nerves and blood vessels, brain function is reduced. This can lead to problems with memory and learning, mood shifts, weight gain, hormonal changes. Over time, even more serious problems may develop (e.g. Alzheimer’s). High blood glucose levels seem able to alter the brain’s billions of connections, essential in linking the many different regions that share functional properties. It can even cause the brain to shrink, medically referred to as atrophy.

Both types of diabetes, 1 and 2 (juvenile onset and adult) have been associated with reduced performance at numerous components of cognitive function. But the exact mechanism explaining the development of this malfunction in thinking abilities is not completely understood. Many studies suggest that changes in brain structure and function are primarily related to hyperglycemia-induced end organ damage, meaning excessive blood sugar levels produce destructive changes. Other theories lay the blame on the vascular disease, altering how well our blood vessels allow the transportation of oxygen and nutrients into the tissues composing our nervous system.

Some of the symptoms of these changes include forgetting things frequently, like missing appointments or scheduled events. Cognitive dysfunction may cause someone to lose their train of thought. They may have trouble following a conversation, or have difficulty making decisions. Reductions in brain function make it hard to finish a task or follow instructions. Someone with diabetes may develop trouble finding their way around places they previously knew well.

People with diabetes are much more likely to have depression than people without. And only about a third of people with diabetes who have depression get diagnosed and treated. This is unfortunate since treatment, whether it’s therapy, medicine, or both, is usually fairly effective. Sadly, “diabetic depression” often gets worse, not better, without treatment.

Various terms have been used to describe this phenomenon, demonstrating the uncertainty regarding this effect of diabetes to cognition. A new but popular term is central neuropathy, used currently in various peer-reviewed studies. Another proposed label is ‘diabetes-associated cognitive decline’ (DACD) to describe the mild to moderate reductions in cognitive function seen with diabetes.

Diabetes has many consequences to health and well-being, as you are now aware. The changes to the nerves in the feet secondary to diabetes is an old problem, recognized and discussed for centuries. But discovering the consequences to the mind and one’s thinking is relatively new. Evidence suggests that cognitive dysfunction should be listed as one of the many complications of diabetes, along with vision, nerve changes in the feet, kidney disease, and heart/artery problems. To those living with someone with diabetes, it may help to know these changes occur and may explain some unusual aspects of their behavior. Chalk this one up as another less than desirable consequence to the very prevalent disease that is diabetes mellitus.

EDITORS NOTE: Dr. Conway McLean is a podiatric physician now practicing foot and ankle medicine in the Upper Peninsula, having assumed the practice of Dr. Ken Tabor. McLean has lectured internationally on surgery and wound care, and is board certified in both, with a sub-specialty in foot orthotic therapy. Dr. McLean welcomes questions, comments and suggestions at drcmclean@penmed.com.