Case Presentation: Syphilis is known as the “Great Imitator” for good reason. With its insidious onset and nonspecific presentation, it is often mistaken for other diagnoses or overlooked altogether. Here, we describe a case of an isolated facial nerve palsy as a rare manifestation of neurosyphilis.

A 53-year-old man presented to urgent care with acute-onset right facial droop preceded by four days of right eye dryness. He was prescribed prednisone and valacyclovir for presumed Bell’s palsy. However, serological testing drawn in clinic later revealed a reactive rapid plasma reagin (RPR) with a titer of 1:64 and a positive fluorescent treponemal antibody absorption (FTA-ABS). Thus, he was referred to our medical center for further evaluation.

The patient denied fevers, chills, headaches, neck stiffness, or skin lesions. He additionally denied recent travel, outdoor activities, tick bites, or known history of sexually transmitted infections. He had formerly been in a monogamous relationship with a male partner, who had been treated for syphilis over 20 years ago, but had otherwise abstained from sex for the past two years.

On exam, the patient was afebrile with no signs of meningismus. Neurological examination demonstrated an isolated right facial nerve palsy. CSF analysis revealed an elevated leukocyte count (47 leukocytes/mcL), elevated protein level (89 mg/dL), and normal glucose level (62 mg/dL). CSF gram stain and culture were negative. Herpes simplex virus (HSV) IgG antibodies and Varicella zoster virus (VZV) IgM antibodies were detected in CSF, but polymerase chain reaction (PCR) identified 0 copies of HSV or VZV DNA. No antibodies to West Nile virus, measles, mumps, or cryptococcus were detected in CSF. Additionally, serologic tests were negative for HIV, Hepatitis C virus, West Nile virus, and cryptococcus. Testing for Lyme disease was not performed, as there was low suspicion based on clinical history. Repeat RPR was reactive with a titer of 1:64 and FTA-ABS was positive. CSF VDRL was positive with a titer of 1:32, confirming the diagnosis of neurosyphilis.

On admission, empiric treatment for neurosyphilis was initiated with intravenous penicillin G (24 million units), and he had marked improvement in facial nerve function on this regimen. He was discharged home on a 14-day course of intravenous penicillin.  

Discussion: This case illustrates a rare presentation of neurosyphilis as unilateral facial nerve palsy. While facial nerve palsy is frequently idiopathic, infectious causes should be considered, including neurosyphilis, HSV, VZV, and Lyme disease. Although incidence of neurosyphilis is low, it is easily diagnosed and treatable.

Conclusions: Neurosyphilis, a great imitator, can be considered on the differential for cranial nerve palsies.