Minocycline hyperpigmentation: model for in situ phagocytic activity of factor XIIIa positive dermal dendrocytes

Pigmentary disorders resulting from the prolonged use of the semisynthetic tetracycline derivative antibiotic, minocycline, are rare but well recognized sequelae of ingestion of this drug. We present two cases of women with bullous pemphigoid who developed blue-black pigmentation in areas of scarring on the legs after oral minocycline therapy. On histologic examination, the deposited pigment was localized within dendritic cells limited to the upper dermis. Immunohistochemical analysis revealed these cells to be factor XIIIa positive dermal dendrocytes which was confirmed by transmission electron microscopy. We believe these cases demonstrate, in-situ, the phagocytic capabilities of this recently described cell population.