Minocycline Pigmentation — SCE Dermatology MCQ

Correct answer: C — Iron chelation by Minocycline metabolites forming insoluble complexes with melanin and haemosiderin in the dermis

The correct answer is C, iron chelation by minocycline metabolites forming insoluble complexes with melanin and haemosiderin in the dermis. This patient shows both classic patterns of minocycline induced pigmentation: type I pigmentation (blue black discolouration within facial acne scars, where iron chelated minocycline metabolites accumulate in macrophages at sites of prior inflammation) and type II pigmentation (blue grey discolouration on the anterior shins in otherwise normal skin, caused by dermal deposition of minocycline degradation products complexed with iron and melanin, taken up by dermal macrophages). Long term minocycline use, as in this patient's two years of treatment, is the key risk factor because pigmentation risk rises with cumulative dose and duration of therapy. Histology with Perls (Prussian blue) staining of the affected dermis confirms iron positive granules, supporting a chelation based deposition mechanism rather than a purely melanotic or exogenous staining process.

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/skin-conditions