Hi Hank,
My Addison's is a result of the surgical removal of my left adrenal gland that had a tumor (pheochromocytoma) when I was 9 years old. The tumor was caused by a mutation in my SDHB gene which I likely inherited from one of my parents. My remaining adrenal is only able to partially compensate for the missing one, resulting in decreased adrenal hormones. My Addison's was not diagnosed until age 42.
Addison's can be caused by a genetic mutation, tuberculosis, an autoimmune disease (the most common cause), etc., but I am not aware that it is caused by neuropathy. As you know, neuropathy can be caused by hundreds of different disorders. In my case, I believe it's caused by marginal cortisol deficiency resulting in an overactive immune system and resulting inflammation in my feet.
Your brother could, if he hasn't already, see an endocrinologist and ask for tests that measure his adrenal hormone levels, and if they're low, get a prescription for what he's missing. He could also get an anti-nuclear antibody test to find out if it's autoimmune. Best of luck to him.
Margaret
@margaret10 Thank-you for the info that my brother might be able to have his levels improved by a prescription. I will pass that on to him in case he does not know. He has been under a doctor's care for years so he may already know his options. Like @sunnyflower he takes a steroid dose each morning. It's unpleasant as he usually gets a bit nauseous right after taking it and sometimes throws up, but he seems to do okay other than that. Thanks again, Hank