Neurosyphilis Diagnosed on the Basis of Pupillary Abnormalities: A Case Report

Neurosyphilis is a condition in which <i>Treponema pallidum</i> invades the central nervous system and may occur at any stage of syphilis. Early diagnosis and treatment are crucial, as advanced disease can result in locomotor ataxia and progressive paralysis. We report a case of neurosyphilis identified on the basis of pupillary abnormalities. A man in his 20s was referred to our hospital with difficulty with near vision in the right eye, after bilateral pupillary dilation had been detected during an eye examination for contact lens prescription at another clinic. Brain MRI revealed no abnormalities, but ocular deviation and motility disturbance developed concurrently. On presentation, visual acuity was 20/20 in the right eye and 20/13 in the left eye. Pupil diameters were 7.5 mm (right) and 6.9 mm (left), with weak direct, indirect, and near reflexes. Right eyelid ptosis was present, with a levator function of 7.5 mm in the right eyelid and 10 mm in the left. The right eye showed limitations in upward, downward, and medial gazes, along with external strabismus. Blood tests for <i>Treponema pallidum</i> antibody and rapid plasma reagin were positive. Contrast-enhanced MRI demonstrated swelling and enhancement of the right oculomotor nerve. Both pupils exhibited mild constriction after 0.1% pilocarpine. The patient was treated with high-dose intravenous penicillin G and three courses of methylprednisolone pulse therapy, resulting in improvement of ocular alignment and motility and partial recovery of pupillary function. This case illustrates that neurosyphilis can present with pupillary abnormalities and oculomotor nerve involvement, even at an early stage. Neurosyphilis should be considered in the differential diagnosis of unexplained pupillary changes.