Clinical and Dermoscopic characteristics of Exogenous ochronosis: Results of a multicenter study by the International Dermoscopy Society Task Force on "Imaging in Skin of Color".

Introduction: Exogenous ochronosis (EO) is an acquired pigmentary disorder characterized by blue-black or gray-blue skin discoloration due to prolonged use of topical hydroquinone (HQ). This study aimed to characterize the clinico-epidemiologic and dermoscopic features of EO in Fitzpatrick skin types III-VI.

Methodology: This retrospective study involved the International Dermoscopy Society Task Force on "Imaging in Skin of Color". Inclusion criteria included confirmed or suspected EO diagnosis in patients of skin of color, and availability of complete clinical history and high quality clinical and dermoscopic images. Cases were classified as definitive EO if histopathologically confirmed, and as probable EO based on characteristic clinical features in HQ users without histopathological confirmation.

Results: The study included 29 patients (93.1% female, mean age 40.04 years). EO was classified as definitive in 41.4% and probable in 58.6% of cases. The malar region was involved in all patients. The mean duration of HQ usage was 15.96 months. Common dermoscopic features observed included obliteration of follicular openings (86.2%), pigment dots (72.4%), and brown amorphous areas (72.4%). Additional features included telangiectasias (51.7%), accentuation of the pigment network (48.3%), arciform or comma-shaped structures (44.8%), white structureless areas (44.8%), and rimming of eccrine openings (31%). Histopathological findings in 12 patients confirmed EO, with banana bodies present in all.

Conclusion: Dermoscopy is a valuable non-invasive diagnostic tool in EO, with obliteration of follicular openings, brown amorphous areas and comma shaped structures being a key feature. Further research is needed to optimize dermoscopic diagnostic criteria and treatment strategies.