We have presented a case of active neurosyphilis with dementia, behavior changes and rare bilateral hippocampal atrophy mimicking EOAD.
A few reports have described the mesiotemporal involvement in neurosyphilis. Several reports have documented unilateral or bilateral asymmetrical mesiotemporal T2 hyperintense lesions on MRI images of the brain in neurosyphilis. This is especially important considering that the clinical presentation of neurosyphilis may also seemingly mimic that of herpes simplex encephalitis or paraneoplastic limbic encephalitis [5, 7–10].
The cause of the mesial temporal T2-weighted hyperintensity is not clear. To our knowledge, there is no pathological study on mesial temporal hyperintensity on T2 weighted images in patients with neurosyphilis. It is suggested that the signal changes represent a combination of edema and gliosis. There are most likely multiple causes for the edema component itself. In meningitis, there are changes in the meningeal and cerebral capillaries, which may increase permeability of the blood–brain barrier, leading to a vasogenic edema component. There may also be some cytotoxic edema and an interstitial edema component, inflammation, meningovasculitis, or microglial hypertrophy [5, 7].
There is no reliable marker to predict the outcome in patients with neurosyphilis following treatment. The duration the illness takes to become symptomatic and the delay in therapeutic intervention are important factors for preventing further progression of the disease. Cases with reversible high signal T2 lesions in the mesial temporal region have been reported [11–13]. The presence of edema is further suggested by the imaging improvement which was found consequent to antibiotic therapy. The residual T2 hyperintense lesion may have a vasculitic origin. The presence of gliosis may be secondary to infection-induced small-vessel ischemic changes.
In our patient, the cognitive and behavioral symptoms, neuropsychological profile, MRI data, and the early age at onset, were compatible with a diagnosis of probable EOAD. Moreover, focal neurological abnormalities have been reported in a rare case of EOAD . However, the serological tests were performed because of the young age and focal neurological abnormalities.
Neurosyphilis is associated with cognitive decline and progressive dementia. A small number of cases have been described mimicking Alzheimer’s disease radiologically. In one of the four cases reported by Zifko et al., MRI of the brain showed atrophy and gliosis over bilateral hippocampi . Another patient reported by Van Eijsden et al.  presented with cognitive and behavioral symptoms. On the MRI brain scan there was medial temporal lobe atrophy which was equivalent to the highest degree of atrophy on a visual rating scale, mimicking EOAD. Our patient showed similar neuropsychological and neuroimaging features with the case described above. Both cases had AD like neuropsychological profiles and a high degree of medial temporal atrophy. Additionally, our patient had focal neurological signs (pyramidal and extrapyramidal signs). CSF abnormalities in both cases showed pleocytosis and elevated protein levels. The follow-up examination showed improvement in neuropsychological results after treatment in both cases.
It is not clear why atrophy occurs in the medial temporal regions. One explanation is that initial infection causes inflammatory T2 hyperintensity which, with no treatment, may disappear at a later stage when the tissues undergo irreversible atrophy . Another explanation may be the emergence of secondary atrophy due to dysfunction in the diffuse cerebral cortex; the medial temporal regions have connections with the cerebral association areas, including the frontal, temporal, and parietal lobes.
This is the first case report of a Bulgarian patient with neurosyphilis, showing progressive cognitive and behavioral changes with bilateral cortical and hippocampal atrophy mimicking EOAD.