Neurosyphilis Exhibiting MRI Abnormalities Mimicking Limbic Encephalitis

Introduction

Neurosyphilis is treatable with antibiotics. Therefore early diagnosis and treatment is important. Making the diagnosis of neurosyphilis is often difficult, because most patients of neurosyphilis present with various symptoms, such as dementia, personality change, confusion, headache, seizures, and visual disorder. We report a case of neurosyphilis was taken to our hospital because of generalized seizures, and revealed MRI abnormalities mimicking limbic encephalitis.

Case report

A 48–year–old man was brought to our hospital emergency room by ambulance because of generalized seizures. He did not have any previous history of seizures or epileptic attacks. Despite intravenous diazepam and a continuous infusion of phenytoin with a loading dose of 750 mg, the seizures continued. Lumber puncture was performed and moderately high cell count and protein were demonstrated, with normal glucose level: 32 cells⁄L, 55 mg⁄dL and 113 mg⁄dL, respectively. Magnetic resonance imaging (MRI) of the brain revealed a high intensity area in the left mesiotemporal lobe on diffusion–weighted images (DWI), T2–weighted images (T2WI) and fluid–attenuated inversion recovery (FLAIR) (Figure 1). We tentatively diagnosed status epilepticus caused by limbic encephalitis and empirically started acyclovir 1500 mg⁄day for 14 days. The seizures completely ceased within 6 hours after admission but dysmnesia and a psychomotor disturbance remained. A Herpes simplex PCR test of cerebrospinal fluid (CSF) on admission was reported as negative, but steroid pulse therapy was started based on the tentative diagnosis of non–herpetic acute limbic encephalitis. However, the follow–up laboratory tests demonstrated an elevation of the serum Treponema pallidum hemagglutination assay (TPHA) to 11800 U⁄ml. A serum test for antibodies against human immunodeficiency virus (HIV) was negative. Further CSF tests were positive for fluorescent treponemal antibodyabsorption test (FTA–ABS) and TPHA. He was diagnosed with neu–rosyphilis and we obtained his past history of treatment for syphilis 20 years previously. After penicillin treatment (24 million unit IV per day for 14 days), the intensity of the initial lesion on the FLAIR images gradually decreased but remained on the follow–up images 35 days after admission, suggesting that this MRI abnormality was not caused by status epilepticus (Figure 1)[1].

Figure 1:  Follow-up MR images on admission and 35 days after admission. FLAIR images (A,C) and diffusion-weighted images (B,D) are shown. An area of high intensity is demonstrated in the left mesiotemporal lobe on diffusionweighted (B) and FLAIR images (A) on admission. This lesion was also observed on FLAIR image (C) as a high intensity area 35 days after penicillin treatment. The high intensity of DWI disappeared (D).