No abstract

A man in his 70s presented to the hospital with dark urine in the setting of increased acetaminophen use. Hours after receiving a computed tomography scan with iodine-based contrast, he developed a pruritic rash. A physical examination revealed scleral icterus, jaundice, and well-circumscribed, bright yellow papules and plaques on his lateral abdomen (Figure). Laboratory findings included an alkaline phosphatase level of 903 U/L (to convert to μkat/L, multiply by 0.0167), total bilirubin level of 13.3 mg/dL (to convert to μmol/L, multiply by 17.104), direct bilirubin level of 11.6 mg/dL, alanine transaminase level of 124 U/L, and aspartate transaminase level of 145 U/L. A biopsy of the liver revealed findings consistent with druginduced liver injury. His rash responded to treatment with antihistamines, and his transaminase levels improved with cessation of acetaminophen use.The clinical presentation of urticaria is of pruritic, migratory skincolored or pink plaques, which are often surrounded by a rim of erythema. Urticaria results from extravasation of plasma into the dermis owing to an idiopathic, immunological, infectious, or physical trigger. In a state of hyperbilirubinemia, urticaria appears yellow owing to the accumulation of bilirubin-rich fluid in the skin. Iodinebased contrast, the presumed culprit in this patient's case, may result in histamine release from mast cell and basophils because of an osmolality effect of the contrast material solution, nonspecific receptor binding of the contrast material, or via complement-kinin activation. 1 The differential diagnosis of yellow urticaria (YU) includes plane xanthomas, nodular amyloidosis, connective tissue nevi, necrobiotic xanthogranuloma, carotenemia, cutaneous mastocytosis, lipoid proteinosis, and pseudoxanthoma elasticum. The evanescent and pruritic nature of the plaques allow YU to be easily distinguished from other conditions in the differential diagnosis.Disease states that lead to hyperbilirubinemia should be ruled out in patients presenting with YU. Yellow urticaria has been reported in the setting of hepatitis, cirrhosis, acute liver failure, choledocholithiasis, antiretroviral therapy, 2 and metastatic disease to the liver. 3,4 Treatment with antihistamines is effective for relieving pruritus and edema. A yellow color may remain after the resolution of urticaria and hyperbilirubinemia because of the affinity of bilirubin for elastin. 4