Pigmented conjunctival cysts following tetracycline/minocycline therapy. Histochemical and electron microscopic observations.

Unpigmented and pigmented cystic epithelial inclusions were found bilaterally within the lower palpebral conjunctiva temporally of a 31-year-old man. He had a history of tetracycline/minocycline therapy for 14 years because of acne vulgaris. The cysts were studied by light and electron microscopy, histochemistry, and ultraviolet light. By light microscopy the unpigmented cysts contained faintly eosinophilic globular material that disclosed yellowish-green autofluorescence indicating the presence of tetracycline/minocycline. The pigmented cysts revealed laminated eosinophilic to brownish concretions that also showed yellowish-green autofluorescence. Autofluorescence, however, decreased with increasing brown pigmentation of the concretions. Histochemically, the pigment, which failed to show the staining characteristics of lipofuscin, melanin or iron, probably represented an oxidation product of tetracycline. By electron microscopy the cysts contained moderately electron dense amorphous material as well as degenerating epithelial cells. The epithelial cells lining the conjunctival cysts, did not contain membrane-bound, large, pigment granules within their cytoplasm as has been demonstrated in the colloid and follicular epithelium of the thyroid following minocycline therapy.