Neurosyphilis Mimicking Herpes Simplex Encephalitis on Magnetic Resonance Imaging: A Case Report.

BACKGROUND Neurosyphilis is a central nervous system infection caused by Treponema pallidum, that can develop at any time after the initial infection. The clinical signs of neurosyphilis are very variable, as well as its radiological features, and it is a diagnostic challenge. Knowledge of clinical symptoms and correct laboratory diagnostics, combined with routine radiological examination and additional diagnostic tools, such as high-resolution, three-dimensional FLAIR sequence, T2-weighted, and T1-weighted contrast-enhanced magnetic resonance imaging (MRI) are key to making an accurate diagnosis of neurosyphilis. CASE REPORT We present the clinical case of a patient who presented a 1-year history of vague clinical symptoms and was misdiagnosed with herpes simplex virus (HSV) encephalitis. Initial head MRI revealed extensive cerebral white matter lesions with cortical contrast enhancement, mainly of anterior and medial parts of the left temporal lobe, as typically seen in HSV encephalitis. Empirical therapy with acyclovir was started until a diagnosis of syphilis was confirmed with laboratory findings. Later, the therapy was changed to penicillin G. The patient's condition improved after receiving targeted treatment. A control MRI scan was performed, and previously detected changes in the brain had decreased significantly. CONCLUSIONS MRI is the imaging of choice to support the diagnosis of neurosyphilis. Our findings suggest that neuroimaging can play an important role in indicating suspicion of syphilitic encephalitis. Enhancement of the anterior and medial parts of the temporal lobe is an atypical imaging finding, and it can simulate an infection with HSV. Early treatment is critical to a positive outcome.