Cicatricial alopecia of the scalp as a manifestation of IgG4-related disease mimicking acne keloidalis nuchae

Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder characterized by tumefactive lesions, storiform fibrosis, and a dense lymphoplasmacytic infiltrate enriched in IgG4-positive plasma cells.¹ Cutaneous involvement is uncommon (approximately 4-6%) and typically presents as erythematous plaques or subcutaneous nodules on the head and neck.¹,² Reports of scarring alopecia associated with IgG4-RD are limited. We herein describe a young Japanese man with scalp IgG4-RD clinically mimicking acne keloidalis nuchae (AKN), in whom alopecia was caused by dermal fibrosis rather than follicular inflammation.A 23-year-old Japanese man first noticed a small papule on his occipital scalp in his late teens, which gradually enlarged over several years. At presentation, he had a 5×3 cm indurated erythematous plaque with scarring and alopecia on the occipital scalp (Fig. 1a,b). The lesion was non-pruritic, non-painful, and showed no pustules or purulent discharge. He had no significant medical history. Laboratory testing showed an elevated serum IgG4 level (153 mg/dL; normal