Clinical and dermoscopic characteristics of exogenous ochronosis: Results of a multicentre study by the International Dermoscopy Society Dermoscopy in Skin of Color Task Force

Background Exogenous ochronosis (EO) is an acquired pigmentary disorder usually characterized by blue-black or grey-blue skin discoloration owing to prolonged use of topical hydroquinone (HQ). Objectives To characterize the clinicoepidemiological and dermoscopic features of EO in Fitzpatrick skin types III-VI. Methods This retrospective study involved the Dermoscopy in Skin of Color Task Force of the International Dermoscopy Society. Inclusion criteria included confirmed or suspected EO diagnosis in patients with skin of colour and availability of complete clinical history and high-quality clinical and dermoscopic images. Patients' cases were classified as definitive EO if histopathologically confirmed and as probable EO based on characteristic clinical features in users of HQ without histopathological confirmation. Results The study included 29 patients (93%, 27/29 women, mean age 40.04 years, SD 9.74). EO was classified as definitive in 41% (12/29) and probable in 59% (17/29) of patient cases. The malar region was involved in all patients. The mean duration of HQ usage was 15.96 months (SD 19.67). Common dermoscopic features observed included obliteration of follicular openings (86%, 25/29), pigment dots (72%, 21/29) and brown amorphous areas (72%, 21/29). Additional features included telangiectasias (52%, 15/29), accentuation of the pigment network (48%, 14/29), arciform or comma-shaped structures (45%, 13/29), white structureless areas (45%, 13/29) and rimming of eccrine openings (31%, 9/29). Histopathological findings in 12 patients confirmed EO, with banana bodies present in all. Conclusions Dermoscopy is a valuable noninvasive diagnostic tool in EO, with obliteration of follicular openings, brown amorphous areas and comma-shaped structures a key feature. Further research is needed to optimize dermoscopic diagnostic criteria and treatment strategies.