Neurosyphilis Masquerading as an Acute Adie's Tonic Pupil: Report of a Case.

We describe the case of a male patient who presented with anisocoria, and was initially diagnosed with an acute Adie's tonic pupil. On subsequent laboratory testing, he was found to have neurosyphilis. Magnetic resonance imaging demonstrated enhancement of the right oculomotor nerve. This case underscores the importance of considering this diagnosis in patients with acute onset internal ophthalmoplegia and hypersensitivity to dilute pilocarpine, even in the absence of other oculomotor nerve findings.