An Infant with Bilateral Keratitis: From Infectious to Genetic Diagnosis

Objective: Challenging differential diagnosisBackground: Tyrosinemia Type II (TYRII) is a rare autosomal recessive inborn error of metabolism caused by deficiency of tyrosine aminotransferase (TAT), leading to hypertyrosinemia. TYRII patients often present in the first year of life with ocular and cutaneous findings, including corneal ulcers, pseudodendritic keratitis, and palmoplantar hyperkeratosis. The corneal involvement is often mistaken for herpes simplex virus (HSV) keratitis, which is a much commoner condition.Case Report: A previously healthy 10-month-old male infant was referred to Ophthalmology for acute onset photophobia. Bilateral dendritiform corneal lesions raised the suspicion for herpetic keratitis. Additionally, a papular, crust-ed lesion was found on his thumb after a few days of hospitalization, also raising concerns about HSV. The patient's clinical condition seemed to improve under intravenous acyclovir and supportive treatment. A con-junctival swab and crusted lesion on the thumb were tested for HSV using a polymerase chain reaction (PCR) technique, and both were negative. Nevertheless, given the clinical presentation and the favorable course of signs and symptoms, hospital discharge was planned with oral acyclovir. It was halted by an alternative diag-nosis of autosomal recessive inborn error of metabolism, tyrosinemia type II, confirmed by elevated plasma ty-rosine level and later by molecular analysis requested as a confirmatory investigation by the genetics medical team.Conclusions: The corneal involvement in TYRII is often mistaken for HSV keratitis, and clinical course alone should not halt further investigations to rule out TYRII. Clinicians should suspect TYRII clinically when its characteristic ocular dendritiform lesions are present, namely in infancy or early childhood, and even in the absence of its typical cutaneous palmoplantar hyperkeratosis plaques.