What causes neuropathy in feet? The answer my cousin's doctor never gave her, after three years of "we may never know"

What causes neuropathy in feet when every test comes back normal? That was the question my cousin Marlene asked at four different appointments over three years, and the only answer she ever got was one long word: idiopathic. She looked it up in the car afterward. It means, more or less, "we don't know."

Marlene is 71. She was the secretary at the same elementary school for twenty-nine years, which means she has spent most of her life being the one person in the building who knows where everything is. Not knowing is not something she does well. And for three years, the thing she didn't know was why her own feet were burning.

It started the way it starts for a lot of us. A little tingle in the big toe on the left side, at night, the summer after she retired. Then both feet. Then the soles, as if she'd walked across hot pavement barefoot, every evening, right when she sat down with her book. By the second winter she was sleeping with her feet outside the covers and a bag of frozen peas on the floor by the bed.

The list they check, and why hers came back clean

If you've asked a doctor what causes neuropathy in feet, you've probably heard the list. It's a good list, and it matters. High blood sugar is the big one. Then low B12, an underactive thyroid, heavy drinking, certain chemotherapy drugs, kidney trouble, and a handful of rarer things. Your doctor runs the blood work, and if one of those lights up, you have a reason and something to work on.

Marlene's lit up nothing. Her A1c was 5.4. Her B12 was fine, her thyroid was fine, her kidneys were fine. She had a nerve conduction test that confirmed the nerves in her feet were in fact damaged, which she said was the most expensive way anyone had ever told her something she already knew.

And that is where a lot of people get stuck. The neurology journals have said for years that somewhere around a quarter to a third of people with this kind of nerve trouble in the feet never get a cause on paper. Not because nothing is happening. Because the list only checks for what usually starts the damage, not for what keeps it going once it has started.

The wire, and the coating on the wire

Here is the part nobody drew for Marlene, so I'll draw it the way my late father, who was an electrician, drew it for me on a napkin once.

Every nerve running down into your feet is like a long wire, and every wire is wrapped in a coating. The medical name is myelin, and it does the same job as the plastic on a lamp cord. It keeps the signal inside, moving fast and quiet. When the coating is whole, you feel the floor, the sheet, the warm water, and nothing else.

When the coating wears thin, the signal starts to leak. Some messages come through too weak, which is the numbness. Some come through too loud, which is the burning and the pins and needles. And the wires that run the farthest, the ones that go all the way to your toes, are the ones that show it first. That is why it nearly always starts in the feet.

So the honest question isn't only "what started it." It's "what is wearing the coating away, night after night, even with normal blood work?"

What she'd already tried

Marlene did everything a sensible person does.

• The prescription. Her doctor started her on a nerve pain medicine. It took the edge off the burning, some nights. It also made her so foggy that she missed the turn into her own church parking lot, and she stopped driving at night.
• The vitamin aisle. A B-complex, then a "nerve formula" from the pharmacy with a picture of a foot on the label. Four months each. Her feet didn't notice.
• The kitchen. Epsom soaks, peppermint oil, a turmeric paste her neighbor swore by. The soaks felt wonderful for twenty minutes.

Every one of those may help somebody, and I would never tell anyone to stop something their doctor gave them. But Marlene finally said it herself at my brother's table that Fourth of July: "All of it turns the volume down. None of it fixes the speaker."

The question my sister-in-law asked

My sister-in-law Joanne was a surgical nurse for most of her life, and she doesn't make small talk at dinner. She listened to all of it and asked Marlene one thing: "Has anybody ever asked you what's eating the coating?"

Nobody had.

Joanne had been reading about a doctor who treated nerve patients for close to three decades and came to a view that isn't on the standard list. In his view, there's a natural process around the nerve that, when it falls out of balance, starts working on the coating slowly, the way rust works on a car you park outside, and it leaves behind a kind of buildup he has his own name for. Sugar can speed it up. Age can speed it up. But in his view it can be at work in people whose blood work is perfectly normal, which would explain a lot of "idiopathic."

I want to be careful here, because I'm a retired bookkeeper and not a neurologist. That is one doctor's view, not a settled fact, and I'm not going to pretend I can explain his whole argument at a dinner table. What I can tell you is that it was the first explanation Marlene had heard in three years that fit what she was feeling, and that it pointed somewhere besides the volume knob.

What Joanne sent her home with

Joanne had been taking something for her own feet, quietly, for most of a year, because nurses are the worst patients there are. She texted Marlene a photo of the bottle that night. It was called NervoLyn. Marlene called me the next morning at six, of course, and read the label to me over the phone, slowly, the way she used to read the lunch menu over the school intercom.

• Alpha lipoic acid, which the company calls one of the most studied antioxidants for the nerves of the hands and feet, there to help protect nerve tissue from the slow, everyday wear. "That's the rust," she said.
• Turmeric extract standardized to 95% curcuminoids, for the body's normal inflammation response around stressed nerves. "Not my neighbor's paste, then."
• Butcher's broom, an old herb for circulation, to keep blood moving all the way down into the legs and feet.
• L-carnitine and Coenzyme Q10, both about energy inside the cells, the fuel a nerve needs to keep up its own repairs.
• Magnesium glycinate, 80 mg, a gentle form of magnesium the company ties to calm nerve signaling and sleep.

"It's not one thing," she said after a minute. "It's somebody who looked at the whole wire." She took the label to her doctor at her next visit. He read it, said it wouldn't interfere with anything she was on, and told her to keep her appointments, which she does. It's one capsule a day, which after her cabinet felt like a vacation. And the company offers a 60-day money-back guarantee, so the worst that could happen was an email.

What she noticed, and the week she wanted to stop

She takes hers at breakfast, with the crossword. This is how it went, from our six a.m. calls.

• Week 1. Nothing. "Same feet, same peas."
• Weeks 2 and 3. A new tingling in the balls of both feet that she didn't like one bit. She almost quit. I'd read that some people notice tingling in a numb area before more normal feeling comes back, and I told her nobody could promise her that's what it was. She kept going because she'd already paid for it, which is how Marlene makes most decisions.
• Month 1. The first night she pulled her feet back under the covers on her own. She didn't notice until morning. She called me before the coffee finished brewing.
• Months 2 and 3. The burning still comes some evenings, usually after a long day on her feet, but shorter, and duller. The peas went back in the freezer for actual dinner. She's driving to Wednesday night choir again.

Why so slow? Because none of it covers anything up. If the coating has been wearing thin for years, the body does its own patching on its own schedule, and the longest wires, the ones to your toes, are the last to get their signal back. The company itself says most people notice early changes around three to four weeks, with fuller results building over eight to twelve weeks of daily use. That's why Marlene, who hates running out of anything, went to the bigger supply after her first bottle.

Who this is for, and who it isn't

It may be worth a look if you're over 50, the burning, tingling or numbness started in your toes and has been climbing, your doctor has checked the basics, and the prescription, the vitamins and the soaks have only turned the volume down.

It is not for you if the numbness came on suddenly, is on one side of your body, comes with leg weakness, a drooping face or trouble speaking, or you have a sore on your foot that isn't healing. Those need a doctor today. If you've never had your blood sugar, B12 and thyroid checked, do that first; it matters. And if you're pregnant or nursing, or take medicine for blood sugar, blood pressure, blood thinning or nerve pain, show your doctor the label before you start.

Why a woman who reads every label said yes

It came down to the guarantee. NervoLyn's own page promises your money back within 60 days if you aren't happy. It's a one-time order, nothing renews on its own, and it's made in the United States in a GMP-certified plant. Marlene had spent three years and more co-pays than she wants to count hearing "we may never know." Two months of one capsule with her crossword, with her money back if nothing changed, was the first bet in a long time that she could actually lose and be fine.

Where she is now

Results vary, and hers are hers. Nobody has told Marlene her nerves are healed, and if they did she'd want it in writing. She still sees her doctor and still checks her feet every night. But she stopped asking what causes neuropathy in feet like hers as if it were a riddle with no answer. "I don't need the long word anymore," she told me. "I needed somebody to look at the wire."

P.S. Last Tuesday she called at six again, and I braced myself. She just wanted to tell me she'd slept with the window open and the covers all the way up, like a normal person. If you're the one at the end of the table with your shoes off underneath it, here's the bottle Joanne texted her that night. And if your toes have gone quiet rather than hot, my brother-in-law's story about the tack in his shoe is the other side of this one.

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