Peripheral polyneuropathy is damage to multiple nerves outside the brain and spinal cord, typically affecting the hands and feet first. It causes numbness, tingling, pain, or weakness that usually starts in the toes and fingers and gradually works its way inward. Between 20% and 50% of people with type 2 diabetes develop it, making diabetes the single most common cause, but dozens of other conditions, medications, and nutritional deficiencies can trigger it too.
How Nerve Damage Develops
Your peripheral nerves are long cables that carry signals between your brain, spinal cord, and the rest of your body. Each nerve fiber has two key parts: the axon (the inner wire that transmits the signal) and the myelin sheath (an insulating layer that speeds transmission along). Polyneuropathy damages one or both of these structures, and which one is affected shapes how the condition behaves.
In axonal damage, the nerve fiber itself breaks down. This typically follows a “dying-back” pattern: the farthest ends of the nerves deteriorate first because they sit the greatest distance from the nerve cell body that keeps them alive and nourished. That’s why symptoms almost always start in the feet before the hands. About 80% of polyneuropathy cases involve this type of symmetrical, length-dependent nerve loss. Diabetes, HIV, and hepatitis C all cause axonal damage.
In demyelinating damage, the insulating sheath breaks down while the inner nerve fiber stays intact. Because the insulation is what allows signals to travel quickly, the main effect is slowed nerve conduction rather than complete signal loss. The good news is that demyelinating neuropathy generally has a better outlook, because the body can rebuild myelin faster than it can regrow an entire nerve fiber.
Sensory, Motor, and Autonomic Symptoms
Peripheral nerves serve three distinct jobs, and polyneuropathy can affect any combination of them. Sensory nerves carry information about touch, temperature, and pain. Motor nerves tell your muscles to move. Autonomic nerves control involuntary functions like heart rate, digestion, and sweating. The mix of symptoms you experience depends on which nerve types are involved.
Sensory Symptoms
The most recognizable signs are numbness, tingling, burning, or a “pins and needles” sensation in the feet and hands. Some people describe a feeling of bugs crawling on the skin. Pain can range from a mild ache to sharp, stabbing episodes. Over time, you may lose the ability to detect light touch, temperature changes, or even injuries to your feet, which is why seemingly minor cuts or blisters can go unnoticed and develop into serious wounds.
Motor Symptoms
When motor nerves are involved, you may notice weakness, particularly in the feet and ankles. Difficulty lifting the front of the foot (called foot drop) is a hallmark sign. Muscles may shrink over time, and coordination problems can make walking feel unsteady. Fine motor tasks like buttoning a shirt can become harder as the hands are affected.
Autonomic Symptoms
Autonomic nerve damage is often the most surprising to people because the symptoms seem unrelated to the nervous system. They can include feeling lightheaded when standing up, a heart rate that suddenly speeds up or slows down, bloating, constipation or diarrhea (sometimes alternating), difficulty emptying the bladder, and erectile dysfunction in men or vaginal dryness in women. Sweating can become unpredictable: certain body parts may sweat excessively while others stay completely dry. Your eyes may also take longer to adjust to darkness, making nighttime driving harder.
One particularly dangerous autonomic effect in people with diabetes is losing the ability to feel the warning signs of low blood sugar, like dizziness, shakiness, or confusion. Without those internal alarms, blood sugar can drop to dangerous levels before you realize anything is wrong.
Common Causes
Diabetes accounts for the largest share of polyneuropathy cases, but the list of potential triggers is long. Causes generally fall into a few broad categories.
- Metabolic and hormonal: Diabetes is the leading cause. Kidney and liver disease can also allow toxins to build up in the blood that damage nerve tissue. Thyroid disorders and other hormonal imbalances can cause tissue swelling that compresses nerves.
- Nutritional deficiencies: Vitamin B12 deficiency is a well-established cause. Research on older adults found that people with poor B12 status had measurably slower nerve conduction speeds and reduced ability to feel light touch compared to those with adequate levels. Roughly 7% of older adults are B12-deficient, with another 10% in a borderline-low range. Chronic alcohol use compounds the problem by both damaging nerves directly and depleting B vitamins.
- Toxic exposures: Chemotherapy is one of the most common medication-related causes. Six major classes of cancer drugs are known to damage peripheral nerves, with rates of nerve injury ranging from 19% to over 85% depending on the drug. Platinum-based drugs carry the highest risk (70% to 100% of patients), followed by taxanes (11% to 87%). Other medications used for HIV, heart conditions, seizures, and autoimmune diseases can also cause neuropathy as a side effect.
- Autoimmune and inflammatory: Conditions where the immune system mistakenly attacks the body’s own nerve tissue, including Guillain-Barré syndrome, can cause rapid or progressive nerve damage.
- Infections: HIV, hepatitis C, Lyme disease, and other infections can directly attack nerve tissue.
- Physical injury: Trauma from accidents, falls, or even repetitive stress can damage peripheral nerves, though this more commonly affects individual nerves rather than causing widespread polyneuropathy.
- Genetic conditions: Inherited forms like Charcot-Marie-Tooth disease exist but are relatively rare compared to acquired causes.
In some cases, no clear cause is ever identified. This is called idiopathic polyneuropathy, and it’s more common than you might expect.
How It’s Diagnosed
Diagnosis typically combines a clinical exam with electrical testing of your nerves. During a nerve conduction study, small electrical impulses are sent through your nerves while sensors measure how fast the signals travel and how strong they are. The test evaluates both motor nerves (by measuring compound muscle action potentials and motor conduction velocity) and sensory nerves (by measuring sensory nerve action potentials and sensory conduction velocity) in the arms and legs.
Slowed conduction speeds point toward demyelinating damage, while reduced signal strength with relatively preserved speed suggests axonal damage. These distinctions matter because they help narrow down the underlying cause. The American Academy of Neurology recommends basing the diagnosis on a combination of symptoms, physical exam findings, and these electrodiagnostic results.
Blood work is usually ordered to check for diabetes, vitamin deficiencies, thyroid problems, kidney and liver function, and markers of autoimmune disease. If a genetic condition is suspected, genetic testing may follow.
Treatment and Pain Management
The most important step in treatment is addressing whatever is causing the nerve damage. For people with diabetes, tighter blood sugar control can slow progression. For B12 deficiency, supplementation can improve nerve function if caught early enough. If a medication is the culprit, switching drugs or adjusting the dose may help.
For neuropathic pain specifically, four options are FDA-approved for painful diabetic neuropathy: duloxetine and pregabalin (both oral medications), tapentadol extended-release (an oral pain reliever), and a high-concentration capsaicin patch applied to the skin. In practice, doctors also prescribe other medications off-label, including older antidepressants, other nerve-calming drugs in the gabapentin family, and certain sodium channel blockers. Finding the right combination often takes some trial and error, since people respond differently to each option.
Physical therapy can help maintain strength, balance, and mobility, especially when motor nerves are involved. Assistive devices like ankle braces may be recommended for foot drop.
Protecting Your Feet
When you can’t fully feel your feet, small problems can escalate quickly. A blister, ingrown toenail, or minor cut that you’d normally notice and treat can go undetected, leading to infections or ulcers that are difficult to heal. Daily foot checks are one of the simplest and most effective habits you can build.
Look for redness, swelling, puncture wounds, calluses, toenail changes, or any shift in foot shape. Wear shoes that fit well and provide protection. A comprehensive foot exam at least once a year, covering sensation, blood flow, structure, and nail health, helps catch problems early. If you have difficulty managing blood sugar or blood pressure, more frequent checks every three to six months are recommended. Any new foot issue warrants a call to your doctor rather than home treatment.
What Recovery Looks Like
Whether nerve damage can be reversed depends largely on the type and cause. Demyelinating neuropathy tends to recover more readily because the body can rebuild the myelin sheath while the underlying nerve fiber remains intact. Axonal damage is slower to heal and, in many cases, only partially reversible, because the nerve fiber itself must regrow from the point of injury back toward the affected area.
Early detection makes a significant difference. Nerve damage caused by a treatable condition, like a vitamin deficiency or a removable toxic exposure, has the best chance of meaningful recovery. When the underlying cause is chronic and progressive, like diabetes, the realistic goal shifts toward slowing further damage, managing pain, and preventing complications. Even in those cases, consistent management can preserve function and quality of life for years.