There is one test that you should have done if not already--Vitimin D blood level. This is among the most overlooked things in modern medicine, and not many physicians are aware of its importance. The latest school of thought is that your blood level should be 50. Anything less than 30 and your risk factors for a host of maladies increases dramatically. I can attest to this from my personal experience.
As a musical entertainer who plays arranger keyboard and sings, there are two aspects of my health that I religiously guard--my hands and my voice. I've always been blessed with a quality singing and speaking voice. and until about 6 years ago my hands were in perfect physical condition. It was then that I began developing splits and cracks along the edges of the nails, which later involved larger areas that would not heal. Similar problems also developed on my legs and buttocks. After visiting several highly rated dermatologists and two years of steroidal treatments, I was referred to internists, infectious disease specialists, and finally a hand surgeon. The hand surgeon said if the problems persisted and the condition of my fingertips worsened, he would likely have to amputate the ends of at least four fingers. It was a pretty scary situation. I would have lost much of my ability to earn a living and my income would drop like a stone.
After 14 doctors, more than $7,000 out of pocket expense that was not covered by insurance, medicare, etc.., I was at my wits end. Then, one night, while performing at a retirement community near my home, one of the residents asked why I was wearing a white cotton glove on my right hand. At the time there was blood seeping through the glove. I told him what I was going though, and he asked to look at my hand. When I showed him he said "My wife had a similar situation, she took vitamin D and within three to four weeks her hands were healed.
We've all heard stories like his, and usually pay no attention to them, figuring it was coincidental. My loving wife of nearly a half-century finally convinced my to give it a try. I began by taking 3,000 IU daily and within three weeks my hands were nearly healed. I had my blood levels tested and the results were astounding. Even after taking 3,000 IU daily, the level was only 32. I increased the dosage to 5,000 IU daily and the level is now 49. That was a year ago and my hands have been clear ever since. Additionally, all of the other lesions are gone as well. Ironically, two of the physicians that were treating me with increasingly higher levels of steroids DO NOT believe that vitamin D played any role in the cure.
A bit of internet research revealed that most of do not have adequate levels of vitamin D in our system. In most instances we try to protect ourself from any and all sun exposure, fearing various skin cancers. In reality, unless you are burnt and blistered your chances of contracting skin cancer from sunlight exposure are pretty slim.
The next thing I discovered is that even with lots of sunlight exposure, as we age we tend to loose our ability to absorb vitamin D from sunlight. Our skin fails to process sunlight the way it did when we were young and active. If you have not done so, I would have that vitamin D level checked ASAP. If it's low, pick up some 5,000 IU gel-caps and begin a daily regiment for at least three months, then have the blood level checked again. In your case, sunlight exposure is something you must avoid as much as possible, so this simple blood test could be extremely important.