is metabolic in nature.

Low thyroid function deposits a substance under the tendons that pinches off the carpal and tarsal tunnels giving the symptoms.

Fluid retention can also cause this. I have found that P5P..a special B6 is very useful for this. Also one gets fluid retention with thiamine problems.
Thiamine 200-300mg a day may help. Or the newer Benfotiamine 150 - 300mg a day (which I switched to recently), is also good. It in fact seems better to me for this edema/fluid issue. Benfotiamine is a special form of thiamine, and also over the counter. You will most likely have to get it online, I have never seen it in stores.
It has just become more affordable too. I get mine at iherb.com

Also hormones will cause carpal tunnel. When I was pregnant I had a terrible time and lost both hands, and couldn't even sign my name. Much of it resolved after delivery, but it returned as just irritating.(instead of debilitating).
So if you take birth control pills or estrogen, you might see carpal tunnel.
This is rather like the pregnancy effects.

If you are gluten sensitive or have other food intolerances, you may see carpal tunnel effects too. Right now I am reacting to nightshades dramatically. (potatoes give me burning). Eliminating a suspected culprit... for 2 weeks and reintroducing it, and getting symptoms is the telling sign.
I would start with gluten first, since it is most common. Then move on to others if you don't react to gluten. Nightshades (tomato peppers potato), Lily family (garlic onion), Corn, dairy, soy are the most common others.

I think, along with some scientists that carpal tunnel is a symptom that something in your metabolic profile is not working right. I think you have to be a detective to target it.

Some other things: If you take drugs for your other issues, some of them may be depleting you of nutrients.
This might show up as carpal tunnel.
And also, eating MSG contain foods (monosodium glutamate) stimulates the nervous system in a negative way.
So check your labels. Restaurant food typically adds this heavily...so anything that tastes really good and seductive
when you eat out can be loaded with this additive. Soups especially or seasoned fries, etc.