Neurosyphilis presenting with unusual hippocampal abnormalities on magnetic resonance imaging and positron emission tomography scans: a case report.

INTRODUCTION: The incidence of neurosyphilis has declined markedly since the introduction of penicillin therapy. While there are a number of case reports in the literature of neurosyphilis causing focal decreased 18F-fluorodeoxyglucose uptake on positron emission tomography/computed tomography scans, to the best of our knowledge this is the first published report of neurosyphilis presenting with intensely increased 18F-fluorodeoxyglucose uptake in the hippocampus.

CASE PRESENTATION: A 55-year-old Caucasian man presented to our facility with acute collapse against a background of memory difficulties over the previous six months. The results of his initial physical examination were normal. He scored 24 out of 30 on the Montreal Cognitive Assessment test. A magnetic resonance imaging scan of his brain revealed high T2 signal intensity and atrophy within the right frontal area in addition to high T2 signal intensity in the bilateral mesial temporal areas. Blood and cerebrospinal fluid analysis revealed an active syphilis infection. An 18F-fluorodeoxyglucose positron emission tomography brain scan showed intensely increased 18F-fluorodeoxyglucose uptake limited to the head of the right hippocampus. He responded to penicillin treatment with an improvement in his cognition, which was further reflected in a complete resolution of the findings previously seen on magnetic resonance imaging and 18F-fluorodeoxyglucose positron emission tomography scans.

CONCLUSIONS: Diagnosis of neurosyphilis can be difficult, as many patients are either asymptomatic or present with non-specific symptoms such as memory disturbance or seizures. This report highlights the importance of considering neurosyphilis in the differential diagnosis when mesiotemporal changes are seen on magnetic resonance imaging or 18F-fluorodeoxyglucose positron emission tomography scans.