Background: Omeprazole has been associated with multiple adverse effects including skin reactions but, to date, cutaneous hyperpigmentation has not been described as an adverse effect of this drug.
Observations: We describe a case of a 52-year-old Caucasian woman who developed skin hyperpigmentation in the upper trunk, mimicking ashy dermatosis, 2 months after initiating omeprazole treatment. Histopathologic examination of a skin biopsy taken from a pigmented macule showed dermal macrophages containing golden-brown granules, which also displayed a sulphur peak on energy-dispersive X-ray microanalysis. High-performance liquid chromatography (HPLC) and mass spectrometry were also performed on the drug and on a biopsy specimen revealing the same chromatograms as well as the same mass spectra.
Conclusions: According to our results, omeprazole itself may induce cutaneous pigmentation and, to our knowledge, this is the first report of this finding.