I hope your grandson has access to specialists in Dermatology and rare disease treatment. My husband had erathema multiforme 3 times. We were fortunate to discover the trigger the first two times. First was a prescription for a statin; next was a viramin supplement; and the last may have been other medical conditions. He was treated by his internist the first time; by his regular dermatologist the second; and referred to the special wound treatment department of a local hospital for the third—which was the most serious. We were able to get home health care for this treatment since I was recovering from hip replacement. That was over three years ago and he’s had additional major surgery since then with no recurrence. I hope your grandson gets relief soon