Diabetes Affects Nervous System

Neuropathy due to excess blood sugar can cause pain and also disturb ability to feel pain

BENGALURU: A beautiful sunrise, the chirping of birds, the fragrance of flowers, the refreshing taste of morning tea, the cool morning air are sensations we enjoy every day, thanks to our nervous system. Each one of these — sight, sound, smell, taste and touch — are conveyed to our brain in the form of electrical signals by our nervous system. The brain interprets these signals to create the corresponding sensations.

The total length of all the nerves in our body is almost 45 miles! In order to process the vast number of nerve signals, the human brain has more than 1 billion nerve cells. But diabetes can bring this empire of communication to its knees.

How does diabetes affect the nerves?

Excess sugar in the blood damages the tiny blood vessels that supply the nerves with nutrients and oxygen. Starved of these, they slowly lose function. This condition is called diabetic neuropathy.

What are the factors that increase risk of diabetic neuropathy?

Based on currently available scientific research, the following factors have been identified:

•    Poor glucose control (higher HBA1c level)
•    Longer duration of diabetes (risk increases with disease duration)
•    Age (risk increases with age)

How common is diabetic neuropathy?

It is the most common complication of diabetes. The longer a person has diabetes, the higher the probability of having neuropathy. As early as 1 year after having diabetes, about 7 per cent will have neuropathy. But this goes up to 50 per cent for those with diabetes for over 25 years.

What are the symptoms?

The symptoms depend on the type of nerves that are affected. The body has three types of nerves:

• Sensory nerves: These nerves connect our sense organs (eyes, ears, nose, tongue, skin) to the brain. They receive sensory stimuli such as how an object appears and how it feels, or how it smells or tastes.
• Motor nerves: These nerves carry signals from the brain to muscles. This enables us to move our body parts, and perform various activities. Remember that these nerves are under our conscious control. That is, they cannot act on their own.
• Autonomic nerves: These nerves are not under our conscious control. They control the vital functions of our body such as breathing, heartbeat, blood pressure, digestion, sweating, pupil size. These vital functions happen on their own.

In addition to the above classification, nerves can be classified based on where they are located:

a) Cranial nerves: These 12 nerves are in the cranium or the skull

b) Peripheral nerves: These nerves are located throughout the body

Both the cranial and peripheral nerves have a combination of sensory, motor and autonomic nerve fibres, and can perform all three basic nerve functions — sensation, muscle control and autonomic.

Diabetes most commonly affects the peripheral nerves: more than 50 per cent of all cases of diabetic neuropathy involves these nerves.  Patients have:

• Numbness of feet and hands, which decreases the ability to feel pain, heat and cold. Patients often complain that they feel like they are “walking on cotton”
• Tingling and burning sensation in hands and feet
• Sharp pains in  hands and feet, which get worse at night
• Extreme sensitivity of skin to even light touch

Sometimes motor function of nerves can also be affected. When this happens, patient may complain of:

•    Weakness in the feet and legs
•   Feeling unsteady while standing or walking

Diabetic neuropathy is often known as “glove and stocking” neuropathy, since it commonly affects the hands and feet. When this is affected by diabetes, it results in a condition known as “autonomic neuropathy”.  This causes debilitating symptoms:

• Variations in the heart rate, ranging from a very rapid heart rate to a very slow heart
• Variations in blood pressure. This is a serious complication. Normally when we say a nerve function is autonomic, it refers to control of the vital functions of the body. When the person stands up, most of the blood tends to pool in the lower legs due to gravity. As a result, the amount of blood entering the heart decreases, and hence less blood is pumped out with each heartbeat. This can cause low blood pressure.

The human body counters this phenomenon, by automatically increasing the heart rate, and by compressing the blood vessels of the skin, legs and abdomen, so that the blood is diverted from the skin, legs and abdomen into the heart. But diabetes sabotages this wonderful mechanism. Therefore, diabetic patients with autonomic neuropathy can feel dizzy when they stand up

• Stomach muscles get paralysed, causing nausea, vomiting, bloating
• Bowel habits are affected, causing severe diarrhoea at night, or severe constipation
• Loss of control over the muscles of the anus and rectum, or lack of sensation in this abdominal pain. This may result in stool accidentally leaking out. This is known as faecal incontinence
• The bladder muscles get paralysed, and may not contract properly to empty the bladder completely
• Men may suffer from impotence (inability to obtain or maintain an erection)
• Excessive sweating while eating, even if the food is not hot or spicy
• The muscles controlling the bladder malfunctions and hence the bladder becomes full. As a result, urine may overflow. So a small amount of urine is left behind in the bladder, and this creates the urge to urinate again and again. Women may suffer from excessive vaginal dryness. Finally, diabetes can also affect the cranial nerves, or the nerves inside our skull, mostly the eyeball. This could result in patients often having diplopia or “double vision”, due to inability of the two eyeballs to focus on a single object.

What are the complications of diabetic neuropathy?

The most dreaded complication is a foot ulcer requiring foot or leg amputation.