Diabetic Neuropathy: Types, Symptoms, Diagnosis and Treatment

What diabetic neuropathy is

Diabetic neuropathy is damage to nerves caused by prolonged high blood glucose, together with the abnormal blood fats, high blood pressure and inflammation that often accompany type 2 diabetes. It is the most common complication of diabetes: about half of people with diabetes develop it, and a proportion already have it when diabetes is diagnosed, reflecting years of undetected high glucose. It also occurs in a milder form in some people with prediabetes.

The mechanism — metabolic injury to nerve fibres plus damage to the small vessels that feed them — is explained in blood sugar and nerve health. This page covers the condition itself: its forms, how it presents, how it is diagnosed and what is done about it.

The four types

Peripheral neuropathy

The most common type, affecting sensation and later movement in the limbs. Because the longest nerve fibres are damaged first, it begins in the toes and feet and progresses upward in a "stocking" distribution, reaching the hands ("glove") only when the legs are affected to around the knee. It is usually symmetrical.

Symptoms fall into two groups:

• Positive symptoms (the nerve misfires): tingling, pins and needles, burning, electric or shooting pain, cramps, heightened sensitivity so that bedsheets are uncomfortable. Often worse at night.
• Negative symptoms (the nerve stops working): numbness, loss of pain and temperature sensation, loss of vibration and position sense, unsteadiness, and in advanced cases weakness and muscle wasting in the feet.

Some people have only pain, some only numbness, many both. Painless neuropathy is the more dangerous because injuries go unnoticed.

Autonomic neuropathy

Damage to the nerves that regulate internal organs. It can affect:

• Digestion — slow stomach emptying (gastroparesis) causing bloating, nausea, early fullness and erratic glucose; constipation, diarrhoea, or both alternating.
• Bladder — incomplete emptying, retention and recurrent infections.
• Blood pressure and heart rate — dizziness or fainting on standing, a resting heart rate that stays high and does not vary, and a blunted response to exercise. Cardiac autonomic neuropathy is associated with increased mortality.
• Sweating — reduced sweating in the feet (dry, cracked skin) and sometimes excessive sweating of the trunk and face, especially when eating.
• Sexual function — erectile dysfunction in men, vaginal dryness and reduced arousal in women.
• Awareness of low blood sugar — the adrenaline symptoms that normally warn of hypoglycemia (shaking, sweating, palpitations) are lost, which is dangerous for people on insulin.

Focal neuropathies

Damage to a single nerve, often sudden. Examples: carpal tunnel syndrome (more common in diabetes), ulnar neuropathy at the elbow, foot drop from peroneal nerve damage, and cranial neuropathies causing double vision or a drooping eyelid. Many focal neuropathies improve over weeks to months.

Proximal neuropathy

Also called diabetic amyotrophy or lumbosacral radiculoplexus neuropathy. Causes severe pain in the hip, buttock or thigh, usually on one side, followed by weakness and wasting of the thigh muscles and difficulty standing from a chair. It mostly affects older men with type 2 diabetes, is often accompanied by weight loss, and usually improves slowly over one to two years.

Risk factors

The duration of diabetes and the level of glucose over that time are the dominant factors. Others that raise risk independently: high triglycerides, obesity, smoking, high blood pressure, tall height (longer nerves), age, kidney disease, and heavy alcohol use. Vitamin B12 deficiency — more common in people on long-term metformin — causes a neuropathy of its own that can compound diabetic neuropathy.

How it is diagnosed

Diagnosis is mostly clinical. Your doctor will ask about symptoms and examine the feet and legs for:

• Pressure sensation with a 10-gram monofilament pressed against the sole — inability to feel it indicates loss of protective sensation.
• Vibration sense with a 128 Hz tuning fork on the big toe.
• Pinprick and temperature sensation.
• Ankle reflexes, which are often reduced or absent.
• Foot inspection for dry skin, calluses, deformity, ulcers and pulses.

Screening is recommended at diagnosis of type 2 diabetes and every year thereafter. Nerve conduction studies are not needed for typical neuropathy; they are used when the picture is atypical. Blood tests for B12, thyroid function and other causes of neuropathy are reasonable, because diabetes is not the only cause and people with diabetes can have another.

Autonomic neuropathy is assessed with heart rate variability tests, lying-and-standing blood pressure, and — for gastroparesis — a gastric emptying study.

Treatment

Slowing progression

Glucose control is the only intervention shown to prevent neuropathy or slow its progression. In type 1 diabetes, intensive control reduced neuropathy by about 60% in the DCCT trial; in type 2 the effect is smaller but present, and it comes with the reduction in other microvascular complications seen in the UKPDS. Managing blood pressure, triglycerides and weight, stopping smoking and limiting alcohol all help. Exercise improves nerve function measures in trials.

Treating pain

Neuropathic pain does not respond well to ordinary painkillers. First-line options with good trial evidence are:

• Duloxetine (a serotonin–noradrenaline reuptake inhibitor)
• Pregabalin and gabapentin (anticonvulsants that act on nerve signalling)
• Amitriptyline or nortriptyline (tricyclic antidepressants, effective but with more side effects in older people)

If one does not help or is not tolerated, another is tried, and combinations are sometimes used. Topical options — capsaicin cream or 8% patches, lidocaine patches — help some people with localized pain. Opioids are avoided where possible because of limited long-term benefit and dependence risk. Alpha-lipoic acid, discussed below, has modest supporting evidence.

Treating autonomic symptoms

Each problem is managed on its own terms: small frequent low-fat meals and sometimes medication for gastroparesis; fibre, fluids and laxatives or antidiarrhoeals for bowel symptoms; scheduled voiding for bladder problems; compression, fluids, salt and sometimes medication for dizziness on standing; PDE5 inhibitors for erectile dysfunction.

Protecting the feet

For anyone with reduced sensation, foot care is a daily task:

• inspect the feet every day, including the soles (use a mirror) and between the toes
• wash and dry carefully; moisturise dry skin but not between the toes
• never walk barefoot, indoors or out
• wear well-fitting shoes and check inside them before putting them on
• cut nails straight across; have calluses treated by a podiatrist rather than at home
• check bath water temperature with a hand or elbow, not a foot
• see a doctor or podiatrist promptly for any cut, blister, colour change or swelling

An annual foot examination is part of diabetes care; people with loss of sensation or deformity need more frequent podiatry review.

Supplements and neuropathy

Alpha-lipoic acid at 600 mg a day has reduced neuropathic symptoms in several trials and is prescribed for diabetic neuropathy in some countries; the effect is modest and clearest with intravenous use. Evidence for benfotiamine (a vitamin B1 derivative) and acetyl-L-carnitine is weaker. Correcting a documented vitamin B12 deficiency is important and different in kind — it treats a separate cause of neuropathy. No supplement repairs damaged nerves, and none replaces glucose control; any should be discussed with the prescriber managing your diabetes.

When to contact a doctor

Report any new tingling, numbness, burning or pain in the feet at your next diabetes review, and sooner if it is progressing quickly, affects one side only, involves weakness, or starts in the hands. See a doctor or podiatrist within a day for any foot wound that is not healing, and the same day for a foot that is red, hot, swollen or painful — with or without a visible wound — as this can signal a deep infection or a Charcot joint. Dizziness on standing, persistent vomiting or bloating after meals, or difficulty passing urine also warrant assessment.

Frequently asked questions

References