Diabetic Peripheral Neuropathy

How diabetes damages the nerves

High blood glucose harms nerves in several ways. It injures the tiny blood vessels that feed them, causes chemical changes inside nerve cells, and triggers inflammation. The longest nerves, those running to the toes, are affected first because they have the most length exposed. As damage progresses, symptoms creep up the legs. When they reach mid-calf, the fingertips often start to be affected, producing the classic stocking-and-glove pattern.

Small nerve fibers (carrying pain and temperature) are often damaged early, causing burning and loss of temperature sense. Large fibers (carrying touch, vibration and position sense) are damaged later, causing numbness and poor balance.

Diabetic peripheral neuropathy is the most common type of diabetic neuropathy. Diabetes can also damage the nerves to internal organs (autonomic neuropathy), single nerves such as the median nerve in carpal tunnel syndrome, and nerve roots in the thigh (diabetic amyotrophy).

Symptoms

Symptoms are usually symmetrical, on both sides:

• Numbness in the feet, or feeling like you are wearing socks when you are not
• Tingling, pins and needles or a crawling feeling
• Burning feet, often worse at night
• Sharp, stabbing or electric-shock pains
• Extreme sensitivity, where even bedsheets hurt (allodynia)
• Loss of feeling for heat, cold or pain, so injuries go unnoticed
• Poor balance and falls, especially in the dark or with eyes closed
• Weak foot muscles, causing clawed toes and high pressure points under the foot

Around half of people with neuropathy have no pain at all. Painless numbness is in some ways more dangerous, because injuries go unnoticed.

Stages

There is no single official staging system, but neuropathy commonly progresses like this:

Risk factors

• Duration of diabetes and high HbA1c over years
• Type 2 diabetes with high blood pressure, high triglycerides and obesity
• Smoking and heavy alcohol use
• Older age and taller height
• Diabetic kidney or eye disease
• Long-term metformin use, which can lower vitamin B12, a separate cause of neuropathy

Diagnosis

Everyone with type 2 diabetes should be screened at diagnosis, and people with type 1 diabetes from 5 years after diagnosis, then at least once a year. The checks are quick and painless:

1. 10-g monofilament test: a nylon filament pressed on several points on the sole. Not feeling it means loss of protective sensation.
2. 128-Hz tuning fork on the big toe joint to test vibration.
3. Pinprick and temperature sensation.
4. Ankle reflexes.
5. Foot inspection: skin, nails, calluses, deformities and pulses.

Blood tests rule out other causes: vitamin B12, thyroid function, kidney function and sometimes protein electrophoresis. Nerve conduction studies are reserved for unusual features, such as weakness, one-sided symptoms or rapid progression.

Treatment

Slowing the damage

• Blood sugar control: strongly prevents neuropathy in type 1 diabetes and modestly slows it in type 2. Aim for the HbA1c target agreed with your care team. Large, rapid drops in HbA1c can briefly worsen pain (treatment-induced neuropathy), so changes should be steady.
• Blood pressure and cholesterol control, stopping smoking, limiting alcohol and regular exercise.

Treating nerve pain

Standard painkillers such as acetaminophen and ibuprofen rarely help neuropathic pain. Guidelines recommend prescription medicines from these groups, each of which helps about a third to half of people:

• Gabapentinoids: pregabalin or gabapentin
• SNRI antidepressants: duloxetine or venlafaxine
• Tricyclic antidepressants: amitriptyline or nortriptyline, often at night
• Sodium channel blockers in some cases

These work best when started low and increased slowly. If one fails, another or a combination is tried. Capsaicin 8% patches and spinal cord stimulation are options for severe pain that does not respond. Opioids are not recommended for long-term use.

Protecting the feet

• Look at your feet every day, including between the toes and the soles (use a mirror).
• Wash daily in lukewarm water. Test the temperature with your elbow, not your foot.
• Never walk barefoot, even at home.
• Wear well-fitting shoes, check inside them for stones, and get specialist footwear if you have deformity.
• Have nails, corns and calluses treated by a podiatrist.
• Never use heating pads, hot water bottles or corn-removal acids on numb feet.

Complications

• Diabetic foot ulcers: about 1 in 4 people with diabetes develop one in their lifetime.
• Infection of soft tissue and bone.
• Charcot foot: collapse of the foot bones in a numb foot, presenting as a hot, swollen foot. It needs urgent offloading in a cast.
• Amputation: most diabetic amputations start with an ulcer.
• Falls and fractures from poor balance.
• Disturbed sleep, low mood and reduced quality of life from chronic pain.

Outlook

Established nerve damage rarely reverses, although early painful symptoms often settle when blood sugar is controlled, and pain can fade as numbness increases. With yearly screening, daily foot checks and prompt treatment of wounds, most foot ulcers and amputations can be prevented.

Frequently asked questions

What are the first signs of diabetic neuropathy in the feet?

Early signs are tingling, pins and needles, burning or numbness in the toes and soles, often worse at night. Some people first notice they cannot feel hot water properly, or find a blister or cut they did not feel happen.

Can diabetic neuropathy be reversed?

Established nerve damage usually cannot be reversed. However, early symptoms can improve with good blood sugar control, and further damage can be slowed with blood sugar, blood pressure and cholesterol control, exercise, and not smoking. Pain can be eased with medicines.

What is the best treatment for diabetic nerve pain?

No single medicine works for everyone. Guidelines recommend pregabalin, gabapentin, duloxetine or a tricyclic antidepressant such as amitriptyline as first choices. If one does not help or causes side effects, another or a combination is tried. Over-the-counter painkillers rarely help.

Why is diabetic neuropathy worse at night?

At night there are fewer distractions, so pain signals are noticed more. Lying still, temperature changes and bedsheets touching sensitive skin can also trigger pain. Taking nerve-pain medicine in the evening and using a bed cradle to lift sheets can help.

Can diabetic neuropathy affect the hands?

Yes. Once neuropathy reaches the mid-calf, the fingertips are often affected, causing numbness or tingling in a glove pattern. People with diabetes are also more prone to carpal tunnel syndrome, which affects the thumb and first three fingers of one or both hands.