Supplementary Material for: Association of Hydroquinone with Nail Discoloration: A Case Report

Introduction: Hydroquinone is topical depigmenting agent that is frequently used to treat hyperpigmentation disorders. Prolonged contact exposure can lead to asymptomatic, reversible orange discoloration of the nail plate. Case Presentation: A 52-year-old woman of Hispanic ethnicity presented to our dermatology clinic for follow up of melasma, two months after initiating hydroquinone therapy. She also was taking isoniazid and rifampin therapies for reactivated tuberculosis. On physical examination, she had sharply demarcated, non-blanching, orange-brown areas of discoloration affecting the distal fingernails. Nail clipping histopathology and serologic testing for vitamin deficiencies, complete cell blood count, and liver and renal functioning were unremarkable. After ruling out alternative etiologies and considering causes such as anti-tuberculosis treatment, a diagnosis of orange nail discoloration secondary to topical hydroquinone use was rendered. Conclusion: The differential diagnosis for orange chromonychia is broad and requires a thorough work up to rule out autoimmune diseases, organ failure (cardiac, hepatic, renal), and vitamin or mineral deficiencies. It is important to consider comorbidities, medications, and contact and exogenous exposures into consideration. Awareness and patient education of this rare side effect may prevent unnecessary distress and, in some cases, avoid unnecessary testing.