The lack of clinical features for bullous pemphigoid (bullae), Henoch-Schönlein (purpura and remnant discoloration), IgM/IgG immune complex vasculitis (purpura), tumid lupus erythematosus (differential distribution of lesions to sun exposed areas), Well’s syndrome (edematous patches), erythema multiforme (bullous or necrotic lesions), cutaneous mastocytosis (macules or papules), cryopyrin-associated periodic syndrome (cold urticaria, fever) further limit diagnosis to idiopathic urticaria. Here, CD40LG is linked to erythema multiforme.