The nervous system can be affected by diabetes mellitus, both directly and indirectly. Examples of direct effects are when blood glucose levels get very high or very low, both of which can cause the brain to not function normally. Examples of indirect cause would be atherosclerosis. Atherosclerosis is accelerated due to diabetes mellitus, and therefore the risk of stroke is increased.
The brain's only source of fuel under normal conditions is glucose, and it likes it in just the right amounts. It actually can tolerate high glucose levels, much better than low. The blood sugar four times normal, for example although not good to have, will not damage the brain. A blood sugar level 1/4 of normal, however, can be life-threatening, leading to seizures, coma or death. The body is very good at giving warning signs of low sugar with symptoms such as sweating, palpitations, anxiety, nausea and tremor. But these are not always completely fail-safe. When glucose gets extremely high, such as over 600 (or is associated with ketosis) then lethargy, and even coma can occur. Often there are precipitating factors that set off these high glucose states such as infection, trauma, stroke, myocardial infarction, pregnancy, or not taking one's insulin. Sometimes it is the initial presentation of diabetes mellitus.
The other direct effect of diabetes is neuropathy. Neuropathy is when the nerve endings furthest from the body; often starting in the feet, do not function normally; producing symptoms such as numbness, tingling, pain, burning, lack of feeling and imbalance. Diabetes is one of the most common causes of this condition. Although there are competing theories as to its cause, nerves work optimally when glucose and insulin are at the correct levels. High glucose levels, metabolites of glucose, or circulation impairment on a microscopic level may be causes of neuropathy. Whatever the cause of neuropathy, it has been shown that the better the glucose is controlled, the less prominent and slower the progression of the symptoms.
Diabetes mellitus can accelerate atherosclerosis as noted above. This can affect different sized arteries, and when a blockage occurs, the part of the body "downstream" from that blockage gets an inadequate blood supply. In the heart, angina or a myocardial infarction can occur; in the legs peripheral vascular disease results; and in the brain, a stroke can occur. Symptoms of stroke vary greatly depending on the area of the brain involved. Weakness or numbness of one side of the body, slurred speech, sudden visual changes, or sudden unsteadiness are common signs. If symptoms resolve within 24 hours this is called a TIA or transient ischemic attack. Sometimes this is called a mini stroke. By this term people can be referring to either symptoms that resolve within 24 hours or symptoms that persist longer than 24 hours, but are minor. Either way, a TIA can be a warning sign and should prompt investigation into its cause and correct as much as possible the risk factors for stroke. These include smoking, hypertension and diabetes, all of which are treatable.
Restless leg syndrome has been shown to occur more frequently in type II diabetes mellitus. This syndrome is an uncomfortable feeling more often in the legs, but can involve the arms as well. It occurs when one is trying to rest or go to sleep. This feeling prompts people to stretch, wiggle or massage their legs or get up and walk. This can occur with or without neuropathy.
Avoiding, minimizing, and delaying complications of diabetes mellitus, neurologic and otherwise, is one of the main goals of diabetes control.
Questions or comments can be addressed to Stuart N. Kieran, MD, c/o Bitterroot Neurology, 1019 West Main Street, Hamilton, MT 59840.