My Father Has A Upper Extremity Rash B/L Arms For

my father has a upper extremity rash B/L arms for months now. multiple treatments with no results. On multiple po ABT, prednisone for months now, multiple topical treatment also with help. What could it be? What would you recommend next? He has PMH of HTN, CABG, PCI, DM2, GI bleed, former smoker,