two other thoughts

Have you been tested for either celiac disease or vitamin E deficiency? Celiac disease is associated with neuropathy and diarrhea or intestinal problems and there can be a lot of weight loss. People with chronic diarrhea may not absorb vitamins–especially the fat soluable ones like vitamin E, D, K, and A– well due to malabsorption. Being low on vitamin E or vitamin K can cause purple spots on the skin from bleeding into the skin/fragility. Being low on vitamin E or D can cause neuropathy (as will vitamin B12 deficiency that also can occur with malabsorption). The good thing about vitamin deficiencies is that one can correct these and get BETTER especially if they can figure out what is causing you to be low to stop the loss, but with replacement anyway. Vitamin E is being given to protect from neuropathy caused by some kinds of chemotherapy. Simple blood tests can look at the levels of vitamin E, D, K, or to test for celiac disease. Celiac disease is not that rare and stopping eating wheat and some other grains (gluten) can help the intestinal part of it. Other forms of inflammatory bowel disease can cause diarrhea, weight loss, and malabsorption, but it would be expected that the colonoscopy would have seen them–but celiac disease can be hard to detect other than the anti-gliaden antibodies or small bowel biopsy (which is done going down from the mouth through the stomach not from below). Since you have impressive intestinal concerns and neuropathy, ask your doctor about celiac disease and about malabsorption caused vitamin deficiencies. Again, if it were any of these, the problem can be TREATED and there may be reversal of some of the problems in the gut and nerves.
WithHope for a cure of these diseases