Unilateral mydriasis as the primary sign of neurosyphilis.

Syphilis can mimic most ocular disorders, and there is no characteristic to distinguish ocular syphilis from other eye diseases. We report a rare case of a 41-year-old man who presented with an Adie's-like pupil as the only feature of neurosyphilis. The patient met the criteria for the diagnosis of neurosyphilis by the finding of positive cerebrospinal fluid-Venereal Disease Research Laboratory (CSF-VDRL) and CSF-Treponema pallidum particle agglutination tests. The patient was then treated with 2 g intravenous ceftriaxone per day for 15 days because of penicillin allergy. Nine months after anti-syphilitic treatment alone, the diameter of the patient's left pupil reduced from 10 to 5 mm. The CSF-VDRL test was negative. It is highly recommended that any patients with ocular disease that does not respond to the routine treatment should undergo syphilis evaluation to avoid misdiagnosis.