Neuropathy has dozens of possible causes, but diabetes is the single most common one. Beyond diabetes, the list includes alcohol use, vitamin deficiencies, chemotherapy, autoimmune diseases, infections, physical compression injuries, and inherited genetic conditions. In roughly 25% to 46% of cases, no cause is ever identified, a proportion that increases with age.
Diabetes and High Blood Sugar
Prolonged high blood sugar is the leading cause of peripheral neuropathy worldwide. The damage isn’t from a single mechanism but from a cascade of biochemical events that all trace back to too much glucose sitting in nerve tissue for too long.
One key pathway involves an enzyme that converts excess glucose into a sugar alcohol called sorbitol. Sorbitol accumulates inside nerve cells, disrupting their internal chemistry. It depletes the cell’s natural antioxidant defenses and reduces production of nitric oxide, a molecule that helps maintain healthy blood flow to nerves. At the same time, the cell loses its ability to efficiently produce energy, weakening the tiny pumps that keep nerve signals firing properly.
High blood sugar also floods the mitochondria (the cell’s power generators) with more fuel than they can handle. This creates a surge of free radicals, reactive molecules that damage cell structures and trigger programmed cell death. The combination of energy starvation and oxidative damage progressively destroys nerve fibers, typically starting in the longest nerves first. That’s why diabetic neuropathy almost always begins in the feet and works its way upward.
Alcohol Use
Heavy, long-term drinking causes neuropathy, and the primary culprit appears to be alcohol itself rather than the nutritional deficiencies that often accompany it. For years, the assumption was that alcohol-related neuropathy stemmed mainly from thiamine (vitamin B1) deficiency, since heavy drinkers tend to eat poorly. But clinical trials have failed to show that thiamine supplements reverse the condition, and a Cochrane review of 13 studies found insufficient evidence that B vitamins are effective treatments.
The strongest predictor of alcohol-related neuropathy is total lifetime dose of alcohol, not age, smoking, liver disease, or any other variable. Ethanol and its breakdown product acetaldehyde appear to directly damage nerve fibers by interfering with the internal transport systems that shuttle nutrients along the length of a nerve cell. Acetaldehyde also generates oxidative stress that compounds the injury. The result is a dying-back pattern where the tips of the longest nerves degrade first, causing numbness and burning pain in the feet and hands.
Vitamin B12 Deficiency
Vitamin B12 plays an essential role in building and maintaining myelin, the insulating sheath that wraps around nerve fibers and allows signals to travel quickly. Without enough B12, the body produces abnormal fatty acids that get incorporated into myelin, leading to faulty insulation or outright breakdown of the sheath. A systematic review of 32 studies found that neuropathy risk increases roughly 50% when B12 levels fall below about 205 ng/L.
B12 deficiency is especially common in older adults (who absorb it less efficiently), people on long-term acid-reducing medications, and those following strict vegan diets without supplementation. Unlike some causes of neuropathy, catching B12 deficiency early often allows partial or full recovery once levels are restored.
Chemotherapy and Other Medications
Chemotherapy-induced neuropathy is one of the most common and frustrating side effects of cancer treatment. The drugs most likely to cause it include platinum-based agents, taxanes, and several others used for blood cancers.
- Platinum drugs: About 40% of patients receiving cisplatin with a taxane develop neuropathy. Oxaliplatin causes an acute, cold-triggered tingling in nearly all patients (which is reversible), plus a longer-lasting neuropathy that becomes more likely at higher cumulative doses. When oxaliplatin is paired with other agents for gastrointestinal cancers, 92% of patients develop some degree of sensory neuropathy.
- Taxanes: Paclitaxel is slightly more neurotoxic than docetaxel. Both cause a dose-dependent neuropathy that typically presents as numbness and tingling in the hands and feet.
- Other agents: Bortezomib, used for multiple myeloma, causes neuropathy in about half of patients. Thalidomide affects 20% to 40%. Vincristine causes neuropathy in most patients once a certain cumulative dose is reached.
These drugs damage nerves through different mechanisms, but the common thread is that they are toxic to the long, vulnerable fibers of peripheral nerves. In many cases, the neuropathy improves after treatment ends, but for some patients it persists for months or years.
Autoimmune Conditions
The immune system can attack peripheral nerves directly, and it does so through at least two distinct patterns.
In Guillain-Barré syndrome (GBS), the immune system produces antibodies that mistake nerve components for foreign invaders, a process called molecular mimicry. These antibodies target specific fat molecules on nerve surfaces and activate a destructive cascade that punches holes in nerve membranes and displaces the sodium channels nerves need to conduct signals. GBS typically develops days to weeks after a viral or bacterial infection and progresses rapidly, often causing weakness that peaks within two to four weeks.
Chronic inflammatory demyelinating polyneuropathy (CIDP) is a slower-burning version. Immune cells infiltrate nerve tissue directly, and specialized cells called macrophages strip myelin from nerve fibers through a process of engulfment and digestion. Antibodies may also deposit on the surface of the cells that produce myelin, compounding the damage. CIDP develops over months rather than days and follows a relapsing or steadily progressive course.
Other autoimmune conditions like lupus and rheumatoid arthritis can also cause neuropathy, though through less well-defined mechanisms that may involve blood vessel inflammation cutting off nerve blood supply.
Infections
Several infections can damage peripheral nerves, either through direct invasion or by triggering an overactive immune response.
Shingles, caused by reactivation of the varicella-zoster virus that lies dormant in nerve cell clusters after chickenpox, is one of the most common infectious causes. The virus reactivates primarily in older adults and immunocompromised people, causing a painful rash along a single nerve’s territory. The most feared complication is postherpetic neuralgia, persistent nerve pain that lingers after the rash clears. Whether this pain results from ongoing viral activity or from permanent damage to sensory nerve cells remains unclear.
Lyme disease, caused by bacteria transmitted through tick bites, frequently affects the peripheral nervous system. Cranial nerve problems (especially facial weakness) and painful nerve root inflammation are the most common manifestations, typically appearing within the first one to two months of infection. In Europe, a specific pattern called Bannwarth syndrome combines painful nerve inflammation with signs of meningitis.
HIV can cause neuropathy both through direct viral effects and as a side effect of certain antiretroviral medications, making it a dual-mechanism problem for affected patients.
Physical Compression and Trauma
Nerves that pass through tight spaces are vulnerable to compression injuries. Carpal tunnel syndrome is the most familiar example: the median nerve runs through a narrow channel in the wrist where normal pressure sits between 2 and 10 mmHg, but simply flexing or extending the wrist can spike that pressure 8 to 10 times higher.
When a nerve is compressed repeatedly, the sequence of damage follows a predictable pattern. First, blood flow to the tiny vessels inside the nerve gets blocked, causing swelling within the nerve itself. That swelling further increases pressure, creating a self-reinforcing cycle. Over time, the myelin insulation breaks down at the compression site, slowing signal transmission. If the compression continues, the nerve fibers themselves begin to degrade. Repetitive wrist movements and sustained awkward positions accelerate this cycle, which is why occupations involving vibrating tools, assembly work, or prolonged keyboard use carry higher risk.
Inherited Neuropathy
Charcot-Marie-Tooth disease (CMT) is the most common inherited form of neuropathy, affecting an estimated 150,000 people in the United States. It’s actually a group of related disorders caused by mutations in genes responsible for building and maintaining either the myelin sheath or the nerve fiber itself.
The most common subtype, CMT1, involves defective myelin. Between 70% and 80% of CMT1 cases trace back to mutations in a single gene called PMP22, which provides instructions for a protein critical to myelin structure. Another 10% to 12% involve the MPZ gene. CMT2 affects the nerve fiber directly rather than its insulation, with mutations in the MFN2 gene accounting for about 20% of cases. Dozens of other genes have been linked to rarer forms.
CMT typically causes slowly progressive weakness and sensory loss that begins in the feet and lower legs during adolescence or early adulthood, though onset and severity vary widely depending on the specific mutation involved.
How Neuropathy Is Diagnosed
When the cause isn’t obvious from your medical history, two electrodiagnostic tests help pin down what’s happening inside the nerve. Nerve conduction studies send small electrical pulses along a nerve and measure how fast the signal travels and how strong it is when it arrives. If the myelin sheath is damaged, the signal slows down. If the nerve fiber itself is degenerating, the signal’s strength drops while its speed stays relatively normal. A difference of more than 50% in signal strength compared to the same nerve on the opposite side is considered abnormal.
Electromyography (EMG) complements this by inserting a thin needle into muscles to listen for abnormal electrical activity. Healthy muscle at rest is electrically silent. When nerve fibers have died and disconnected from muscle, the muscle produces small spontaneous bursts of activity called fibrillations. In chronic, slowly progressive neuropathies like inherited forms, the remaining healthy nerve fibers compensate by taking over orphaned muscle fibers, producing signals 5 to 10 times larger than normal. The pattern of these abnormalities helps distinguish between acute and chronic nerve damage, and between conditions that attack myelin versus the nerve fiber itself.
Blood tests typically accompany these studies to check for diabetes, B12 levels, thyroid dysfunction, inflammatory markers, and other treatable causes. Since up to 46% of cases remain unexplained even after a thorough workup, the diagnostic process sometimes becomes one of ruling out reversible causes rather than arriving at a definitive answer.