A rare presentation of neurosyphilis mimicking a unilateral Adie's tonic pupil.

We describe a case of a female patient who presented with anisocoria and was initially diagnosed with a right acute Adie's pupil on the basis of a right tonic pupil with absent oculomotor or neurological findings and hyper-responsiveness to dilute Pilocarpine. Two months later, the patient returned with bilateral tonic pupils and limitation of extraocular movement in the right eye. Subsequent laboratory testing revealed neurosyphilis. Our case, only the second ever reported, emphasizes the importance of considering the diagnosis of neurosyphilis in patients presenting with an isolated acute tonic pupil.