Minocycline-related cutaneous hyperpigmentation as demonstrated by light microscopy, electron microscopy and X-ray energy spectroscopy.

A 70-year-old patient with a chronic cutaneous ulcer treated by minocycline hydrochloride developed hyperpigmentation of the forearms. Biopsy material was studied by light microscopy, electron microscopy and X-ray energy spectroscopy. Granular gold-brown pigment was found in dermal histiocytes and eccrine myoepithelial cells, which gave positive reaction with Prussian blue and Fontana-Masson stains. Electron microscopy revealed intracytoplasmic granules of dark, homogeneous material and small fine particles. X-ray energy spectroscopy showed iron and other elements in smaller amounts. The different types of minocycline-related hyperpigmentation and the possible pathomechanism are discussed with special regard to the importance of the diagnostic methods.