Neurosyphilis: An underdiagnosed entity

Alzheimer's Disease and Neurosyphilis: Meaningful Commonalities and Differences of Clinical Phenotype and Pathophysiological Biomarkers

BACKGROUND

Neurosyphilis-associated cognitive and behavioral impairment- historically coined as "general paralysis of the insane"- share clinical and neuroradiological features with the neurodegenerative disease spectrum, in particular Alzheimer's disease (AD). Anatomopathological similarities have been extensively documented, i.e., neuronal loss, fibrillary alterations, and local amyloid-β deposition. Consequently, accurate classification and timely differential diagnosis may be challenging.

OBJECTIVE

To describe clinical, bio-humoral, brain MRI, FDG-PET, and amyloid-PET features in cases of neurosyphilis with an AD-like phenotypical presentation, as well as clinical outcome in terms of response to antibiotic therapy.

METHODS

We selected the studies comparing patients with AD and with neurosyphilis associated cognitive impairment, to investigate candidate biomarkers classifying the two neurological diseases.

RESULTS

The neuropsychological phenotype of general paralysis, characterized by episodic memory impairment and executive disfunction, substantially mimics clinical AD features. Neuroimaging often shows diffuse or medial temporal cortical atrophy, thus contributing to a high rate of misdiagnosis. Cerebrospinal fluid (CSF)-based analysis may provide supportive diagnostic value, since increased proteins or cells are often found in neurosyphilis, while published data on pathophysiological AD candidate biomarkers are controversial. Finally, psychometric testing using cross-domain cognitive tests, may highlight a wider range of compromised functions in neurosyphilis, involving language, attention, executive function, and spatial ability, which are atypical for AD.

CONCLUSION

Neurosyphilis should be considered a potential etiological differential diagnosis of cognitive impairment whenever imaging, neuropsychological or CSF features are atypical for AD, in order to promptly start antibiotic therapy and delay or halt cognitive decline and disease progression.

Neurosyphilis Presenting as an Atypical Case of Posterior Placoid Chorioretinitis in a Young, HIV-Negative Male

Ocular syphilis can occur at any time after initial infection and most commonly presents as posterior uveitis or panuveitis, although many other ocular findings have been documented. We present the case of a young, otherwise healthy Caucasian HIV-negative male who presented with acute onset of photopsias, floaters, and a rapidly progressive unilateral scotoma who was originally diagnosed with acute zonal occult outer retinopathy (AZOOR) and started on a high dose prednisone taper. Although his clinical symptoms improved on corticosteroids, he was later switched to Penicillin G treatment when his blood and cerebrospinal fluid (CSF) testing demonstrated syphilis as his underlying diagnosis. Given his ocular findings on the exam and reactive syphilitic testing, he was ultimately diagnosed with acute syphilitic posterior placoid chorioretinitis (ASPPC). Our patient's clinical improvement after a high-dose prednisone trial offers further evidence of an autoimmune component to the pathophysiology of ASPPC.