I am sorry, but I could not find anything on the internet that addressed this either. The closest I found was "dry gangerine" which can occur in people with auto-immune diseases. Here is a bit of information about that condition:
More common in people with diabetes
and autoimmune diseases
, dry gangrene usually affects the hands and feet
. It develops when blood flow to the affected area is impaired, usually as a result of poor circulation. Unlike other types of gangrene, infection is typically not present in dry gangrene. However, dry gangrene can lead to wet gangrene if it becomes infected.
I wish that I could be of more help. Please do have your doctor look at this as, regardless of what it is, it sounds as if it is something to take seriously and get treatment for asap. Best of luck to you.
Peace and Blessings