• Ian Straehley, Neilmegh Varada, Ingmar Prokop, and Cassandra Muxen.
• Oregon Health and Science University, 3831, SW Sam Jackson Park Rd, Portland, OR, USA.
• Am J Ophthalmol Case Rep. 2020 Jun 1; 18: 100679.

PurposeThis case report describes a case of Horner syndrome resulting from central nervous system (CNS) toxoplasmosis in an immunocompromised patient. Horner Syndrome is a neurological condition characterized by unilateral miosis, ptosis with apparent enophthalmos, and anhidrosis due to inhibition of the sympathetic pathway. The ocular sympathetic pathway runs from the posterolateral hypothalamus to the ophthalmic branch of the trigeminal nerve (cranial nerve V1). Central nervous system (CNS) toxoplasmosis infection is typically only seen in immunocompromised patients. To our knowledge, toxoplasmosis has never been reported as a cause of Horner syndrome.ObservationsA forty-four-year-old Caucasian male was admitted to the hospital for left upper extremity paresthesias, gait instability, and painful vesicular skin lesions, and Horner syndrome. Upon review, he had an 18-year history of HIV initially controlled on anti-retrovirals but had been lost to follow-up for several years until he developed severe headaches determined to be caused by Toxoplasmosis lesions in his brain. Over several months he was treated for the Toxoplasmosis but had poor adherence to medications. After subsequent admission and workup, we found multi-focal ring enhancing lesions on MRI in the basal ganglia, hypothalamus, thalamus, and internal capsule. We postulated that the hypothalamic lesion was the cause of his Horner syndrome. After treatment for both toxoplasmosis and HSV his Horner syndrome and other neurologic symptoms resolved.Conclusions And ImportanceThis is the first reported case of Horner syndrome resulting from CNS toxoplasmosis. This case report and the accompanying questions provide an opportunity to review and explore the neuroanatomy and subtle symptomatic differences between various etiologies of Horner syndrome (primary, secondary, tertiary) in the context of a novel presentation. In conclusion, toxoplasmosis should be considered when investigating Horner syndrome in immunocompromised patients.© 2020 Published by Elsevier Inc.

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