Neurosyphilis and paraneoplastic limbic encephalitis: important differential diagnoses

Mimickers of autoimmune encephalitis: a literature review

Autoimmune encephalitis (AIE) is a rapid, progressive neurological disorder characterized by nervous system inflammation. While the Graus criteria are the best known criteria for AIE diagnosis, other differential diagnoses meeting the Graus criteria must be considered before management. This narrative review discusses the most common etiologies that resemble AIE. We suggest routine exclusion of mimickers meeting the Graus criteria before confirming an AIE diagnosis. We reviewed 28 studies including 356 patients. The main initial diagnosis was AIE, then paraneoplastic limbic encephalitis and anti-N-methyl-D-aspartate receptor encephalitis. Only 194 patients met the possible Graus criteria. The most frequent conditions among the total population were dementia, other neurodegenerative diseases, and psychiatric and functional neurological disorders. AIE is often misdiagnosed, leading to unnecessary treatment. Despite publication of the Graus criteria, medical cases mimicking this condition are being published. Many neurological diseases entering the differential diagnosis of AIE could be excluded through a detailed history, neurological examination, laboratory analysis, and other investigations, including cerebrospinal fluid and brain magnetic resonance imaging. However, some differential diagnoses complied with the possible Graus criteria, with some having concurrent antineuronal antibodies, which were considered true mimickers. AIE diagnosis suspicion is primarily clinical, but a definitive diagnosis requires various diagnostic tools.

Mimics of Autoimmune Encephalitis: Validation of the 2016 Clinical Autoimmune Encephalitis Criteria

BACKGROUND AND OBJECTIVES

The clinical criteria for autoimmune encephalitis (AE) were proposed by Graus et al. in 2016. In this study, the AE criteria were validated in the real world, and common AE mimics were described. In addition, criteria for probable anti-LGI1 encephalitis were proposed and validated.

METHODS

In this retrospective cohort study, patients referred to our national referral center with suspicion of AE and specific neuroinflammatory disorders with similar clinical presentations were included from July 2016 to December 2019. Exclusion criteria were pure cerebellar or peripheral nerve system disorders. All patients were evaluated according to the AE criteria.

RESULTS

In total, 239 patients were included (56% female; median age 42 years, range 1-85). AE was diagnosed in 104 patients (44%) and AE mimics in 109 patients (46%). The most common AE mimics and misdiagnoses were neuroinflammatory CNS disorders (26%), psychiatric disorders (19%), epilepsy with a noninflammatory cause (13%), CNS infections (7%), neurodegenerative diseases (7%), and CNS neoplasms (6%). Common confounding factors were mesiotemporal lesions on brain MRI (17%) and false-positive antibodies in serum (12%). Additional mesiotemporal features (involvement extralimbic structures, enhancement, diffusion restriction) were observed more frequently in AE mimics compared with AE (61% vs 24%; p = 0.005). AE criteria showed the following sensitivity and specificity: possible AE, 83% (95% CI 74-89) and 27% (95% CI 20-36); definite autoimmune limbic encephalitis (LE), 10% (95% CI 5-17) and 98% (95% CI 94-100); and probable anti-NMDAR encephalitis, 50% (95% CI 26-74) and 96% (95% CI 92-98), respectively. Specificity of the criteria for probable seronegative AE was 99% (95% CI 96-100). The newly proposed criteria for probable anti-LGI1 encephalitis showed a sensitivity of 66% (95% CI 47-81) and specificity of 96% (95% CI 93-98).

DISCUSSION

AE mimics occur frequently. Common pitfalls in AE misdiagnosis are mesiotemporal lesions (predominantly with atypical features) and false-positive serum antibodies. As expected, the specificity of the criteria for possible AE is low because these criteria represent the minimal requirements for entry in the diagnostic algorithm for AE. Criteria for probable AE (-LGI1, -NMDAR, seronegative) and definite autoimmune LE are applicable for decisions on immunotherapy in early disease stage, as specificity is high.

Imaging features of neurosyphilis

Syphilis is an infectious disease caused by the spirochete Treponema pallidum, subspecies pallidum. Although its incidence has declined after the widespread availability of penicillin, it has recently re-emerged, especially in men who have sex with men and in people living with human immunodeficiency virus (HIV). The neurological manifestations of syphilis, generally known as neurosyphilis, may appear at any time during the infection, including the initial years after the primary infection. Neurosyphilis can be asymptomatic, only with cerebrospinal fluid abnormalities, or symptomatic, characterized by several different clinical syndromes, such as meningitis, gumma, meningovascular, brain parenchyma involvement, meningomyelitis, tabes dorsalis, and peripheral nervous system involvement. However, these syndromes may simulate several other diseases, making the diagnosis often a challenge. In addition, syphilis can also be vertically transmitted from mother to child during pregnancy, leading to neurological manifestations. Neuroimaging is essential to demonstrate abnormal brain or spinal cord findings in patients with neurosyphilis, aiding in the diagnosis, treatment, and follow-up of these patients. This article aims to review the imaging features of neurosyphilis, including the early and late stages of the infection.

[A case of neurosyphilis presenting as sudden onset of limbic encephalitis]

A 52-year-old male was carried to hospital by ambulance, because of an abrupt abnormal behavior and impaired consciousness. Soon after the arrival, the patient started a generalized seizure. Although the seizure was stopped by Midazolam, amnesia were observed. With meningeal irritation signs, in addition to the clinical course, the patient was thought to develop limbic encephalitis. The cause of the encephalitis was diagnosed as neurosyphilis because of the positive serum and CSF syphilis reactions, and the patient was treated with penicillin G from the first admission day on. Steroid pulse therapy was also conducted, followed by acyclovir since herpes encephalitis could not be ruled out; the brain MRI showed left-side dominant T₂/FLAIR high intensity lesions in the bilateral temporal lobes and left hippocampus. With the treatment progression, the amnestic syndrome improved and the patient returned to work. Although neurosyphilis is a rare cause of acute onset limbic encephalitis, it is important to keep the possibility of this disease in mind in making a treatment plan.

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 autoimmune limbic encephalitis: A case report and literature review

RATIONALE

Neurosyphilis presenting as limbic encephalitis (LE) is an important differential diagnosis of autoimmune LE (ALE) defined by Graus in 2016. However, data on the clinical differences and similarities between neurosyphilis presenting as LE and ALE are limited. Herein, we report neurosyphilis presenting as ALE that fulfilled the main items of the Graus ALE criteria. Moreover, a literature review of neurosyphilis presenting as LE was performed.

PATIENT CONCERNS

A 66-year-old Japanese man developed nonconvulsive status epilepticus. He presented with progressive personality change and working memory deficits within 3 months prior to admission. A hyperintense lesion localized in the bilateral medial temporal area was observed on T2-weighted fluid-attenuated inversion recovery brain magnetic resonance imaging. Cerebrospinal fluid analysis showed mild pleocytosis and the presence of oligoclonal band. However, in-house assays did not detect antineuronal antibodies. Electroencephalogram showed lateralized rhythmic delta activity in the right temporal area. The serum and cerebrospinal fluid serological and antigen tests for syphilis had positive results.

DIAGNOSIS

ALE was initially suspected based on the patient's symptoms and ancillary test findings that fulfilled the Graus ALE criteria. However, based on the positive confirmatory test results for syphilis, a diagnosis of neurosyphilis was eventually made.

INTERVENTION

The patient received intravenous midazolam, oral levetiracetam, and lacosamide to control nonconvulsive status epilepticus. In addition, he was treated with intravenous benzylpenicillin at a dose of 24 million units/day for 14 days.

OUTCOMES

The patient's cognitive function relatively improved after antibiotic treatment. However, he presented with persistent mild working memory deficit, which was evaluated with the Wechsler Adult Intelligence Scale, 3rd edition. Therefore, on day 103 of hospitalization, he was transferred to another hospital for rehabilitation and long-term care due to limitations in performing activities of daily living.

LESSONS

The present case was diagnosed with neurosyphilis presenting as ALE, but meanwhile, in most case, neurosyphilis presenting as LE developed at a slower progressive rate, and it had a broader or restricted involvement on brain MRI than ALE based on the literature review. Therefore, an appropriate differential diagnosis of LE can be obtained by identifying clinical differences between the 2 conditions.

Neuropathology of the temporal lobe

Neuropathological examination of the temporal lobe provides a better understanding and management of a wide spectrum of diseases. We focused on inflammatory diseases, epilepsy, and neurodegenerative diseases, and highlighted how the temporal lobe is particularly involved in those conditions. Although all these diseases are not specific or restricted to the temporal lobe, the temporal lobe is a key structure to understand their pathophysiology. The main histological lesions, immunohistochemical markers, and molecular alterations relevant for the neuropathological diagnostic reasoning are presented in relation to epidemiology, clinical presentation, and radiological findings. The inflammatory diseases section addressed infectious encephalitides and auto-immune encephalitides. The epilepsy section addressed (i) susceptibility of the temporal lobe to epileptogenesis, (ii) epilepsy-associated hippocampal sclerosis, (iii) malformations of cortical development, (iv) changes secondary to epilepsy, (v) long-term epilepsy-associated tumors, (vi) vascular malformations, and (vii) the absence of histological lesion in some epilepsy surgery samples. The neurodegenerative diseases section addressed (i) Alzheimer's disease, (ii) the spectrum of frontotemporal lobar degeneration, (iii) limbic-predominant age-related TDP-43 encephalopathy, and (iv) α-synucleinopathies. Finally, inflammatory diseases, epilepsy, and neurodegenerative diseases are considered as interdependent as some pathophysiological processes cross the boundaries of this classification.

Imaging Characteristics of Brain SPECT, PET, and MRI in Neurosyphilis

The incidence of neurosyphilis has declined since effective penicillin therapy against Treponema pallidum was introduced. However, the diagnosis of neurosyphilis early in the disease course is very important in order to select appropriate antibiotic therapy. We report brain MRI, SPECT with Tc-99m ECD, and PET with F-18 FDG findings before antibiotic therapy in a neurosyphilis patient with neurological symptoms. The cerebral cortices showed hypoperfusion with a patchy distribution on SPECT and foci with high signal intensity on MRI, suggesting ischemia. Brain PET showed areas with hypometabolism in the temporoparietal lobes bilaterally.

Neurosyphilis Mimicking Autoimmune Encephalitis: A Case Report and Review of the Literature

Neurosyphilis may imitate a wide range of neurological and psychiatric diseases, including autoimmune encephalitis. To avoid further cognitive decline and morbidity, early recognition and adequate treatment are of particular importance in both neurosyphilis and autoimmune encephalitis. In case of a strong clinical suspicion of a diagnosis of autoimmune encephalitis, guidelines recommend initiating immunotherapy even in the absence of immunological confirmation. Here, a case of neurosyphilis is reported in which the potential overlap in clinical presentation of autoimmune encephalitis and parenchymatous neurosyphilis is discussed. The here reported data suggest that, in cases presenting with new onset focal epilepsy, slowing of electroencephalographic activity over the temporal regions and magnetic resonance imaging suggestive of swelling of the amygdala, neurosyphilis should be excluded prior to initiation of immunotherapy for suspected autoimmune encephalitis.

Usefulness of Positron Emission Tomography in Patients with Syphilis: A Systematic Review of Observational Studies

Background:

Diagnosis of syphilis is difficult. Follow-up and therapy evaluation of syphilitic patients are poor. Little is known about positron emission tomography (PET) in syphilis. This review was to systematically review usefulness of PET for diagnosis, disease extent evaluation, follow-up, and treatment response assessment in patients with syphilis.

Methods:

We searched PubMed, EMBASE, SCOPUS, Cochrane Library, Web of Science, ClinicalTrials.gov, and three Chinese databases (SinoMed, Wanfang, and CNKI) for English and Chinese language articles from inception to September 2016. We also collected potentially relevant studies and reviews using a manual search. The search keywords included the combined text and MeSH terms “syphilis” and “positron emission tomography”. We included studies that reporting syphilis with a PET scan before and/or after antibiotic treatment. The diagnosis of syphilis was based on serological criteria or dark field microscopy. Outcomes include pre- and post-treatment PET scan, pre- and post-treatment computed tomography, and pre- and post-treatment magnetic resonance imaging. We excluded the articles not published in English or Chinese or not involving humans.

Results:

Of 258 identified articles, 34 observational studies were included. Thirty-three studies were single-patient case reports and one study was a small case series. All patients were adults. The mean age of patients was 48.3 ± 12.1 years. In primary syphilis, increased fluorodeoxyglucose (FDG) accumulation could be seen at the site of inoculation or in the regional lymph nodes. In secondary syphilis with lung, bone, gastrointestinal involvement, or generalized lymphadenopathy, increased FDG uptake was the most commonly detected changes. In tertiary syphilis, increased glucose metabolic activity, hypometabolic lesions, or normal glucose uptake might be seen on PET. There were five types of PET scans in neurosyphilis. A repeated PET scan after treatment revealed apparent or complete resolution of the asymmetry of radiotracer uptake.

Conclusion:

PET is helpful in targeting diagnostic interventions, characterizing disease extent, assessing nodal involvement, and treatment efficacy for syphilis.

Autoimmune encephalopathies

Over the past 10 years, the continual discovery of novel forms of encephalitis associated with antibodies to cell-surface or synaptic proteins has changed the paradigms for diagnosing and treating disorders that were previously unknown or mischaracterized. We review here the process of discovery, the symptoms, and the target antigens of 11 autoimmune encephalitic disorders, grouped by syndromes and approached from a clinical perspective. Anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis, several subtypes of limbic encephalitis, stiff-person spectrum disorders, and other autoimmune encephalitides that result in psychosis, seizures, or abnormal movements are described in detail. We include a novel encephalopathy with prominent sleep dysfunction that provides an intriguing link between chronic neurodegeneration and cell-surface autoimmunity (IgLON5). Some of the caveats of limited serum testing are outlined. In addition, we review the underlying cellular and synaptic mechanisms that for some disorders confirm the antibody pathogenicity. The multidisciplinary impact of autoimmune encephalitis has been expanded recently by the discovery that herpes simplex encephalitis is a robust trigger of synaptic autoimmunity, and that some patients may develop overlapping syndromes, including anti-NMDAR encephalitis and neuromyelitis optica or other demyelinating diseases.

Mesiotemporal changes on magnetic resonance imaging in neurosyphilis

We report a case of neurosyphilis with magnetic resonance imaging (MRI) brain scan findings compatible with a diagnosis of herpes simplex encephalitis with negative testing for herpes simplex virus in the cerebral spinal fluid. An extensive review of the literature has been undertaken revealing 24 cases worldwide where there are mesiotemporal changes on MRI concurrent with a diagnosis of neurosyphilis. Therefore, it is now well established that neurosyphilis, 'the great imitator', should be considered in the differential diagnosis in all patients demonstrating mesiotemporal changes on MRI, changes usually seen in herpes simplex encephalitis.

Neurosyphilis

No portion of the central nervous system is immune to the ravages of syphilis. Infection by Treponema pallidum can affect the meninges, brain, brainstem, spinal cord, nerve roots, and cerebral and spinal blood vessels. As a consequence, the disease may present in diverse and, at times, diagnostically challenging fashions. Neurologic manifestations of syphilis may develop within months of the initial infection or, alternatively, take decades to appear. Although approximately one-third of individuals infected by T. pallidum display cerebrospinal fluid abnormalities suggestive of invasion of the central nervous system by the organism, only a fraction of these develop clinically significant neurologic manifestations. The features of neurosyphilis may be modified by the concomitant presence of immunosuppressive agents or conditions such as HIV/AIDS. The epidemiology of neurosyphilis has largely paralleled that of syphilis in general. A dramatic decline occurred by the early 1950s as a consequence of public health measures and the widespread use of antibiotics. The incidence had increased by the onset of the AIDS pandemic and has since corresponded with the adoption of safe sex practices. The CSF Venereal Disease Research Laboratory (VDRL) test remains the "gold standard" for diagnosis, but is not invariably positive. Penicillin remains the most effective and recommended therapy.

Syphilitic limbic encephalitis revealed by status epilepticus

Limbic encephalitis (LE) is an inflammatory disorder of the limbic system; the clinical features are diverse, characterised by the development of neuropsychiatric symptoms, its aetiologies are various; syphilis is a rare entity. We report the case of a 50-year-old-man with syphilitic LE revealed by an inaugural status epilepticus. Diagnosis was made considering clinical, biological and radiological arguments. The patient received specific treatment for neurosyphilis. Evolution was marked by improved neuropsychological symptoms, the negativity of venereal disease research laboratory test in blood and cerebrospinal fluid and regression of the mesiotemporal signal abnormalities on MRI.

The diagnosis and treatment of limbic encephalitis

The term limbic encephalitis (LE) was first introduced in 1968. While this disease was initially considered rare and is often fatal with very few treatment options, several reports published in the last decade provide a better description of this condition as well as possible causes and some cases of successful treatment. The clinical manifestation of LE is primarily defined by the subacute onset of short-term memory loss, seizures, confusion and psychiatric symptoms suggesting the involvement of the limbic system. In addition, EEG often shows focal or generalized slow wave or epileptiform activity, and MRI findings reveal hyperintense signals of the medial temporal lobes in T2-weighted or FLAIR images. The current literature suggests that LE is not a single disorder but is comprised of a group of autoimmune disorders predominantly affecting the limbic system. Before the diagnosis of LE can be determined, other causes of subacute encephalopathy must be excluded, especially those resulting from infectious aetiologies. LE has previously been regarded as a paraneoplastic phenomenon associated with the classical onconeuronal antibodies that are primarily directed against intracellular antigens. However, recent literature suggests that LE is also associated with antibodies that are directed against cell surface antigens, and these cases of LE display a much weaker association to the neoplasm. The treatment options for LE largely depend on the aetiology of the disease and involve the removal of the primary neoplasm. Therefore, a search for the underlying tumour is mandatory. In addition, immunotherapy has been successful in a significant number of patients where LE is not associated with cancer.

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.

MRI of neurosyphilis presenting as mesiotemporal abnormalities: a case report

The high signal intensities in bilateral mesiotemporal lobes on T2-weighted images are typical findings of herpes encephalitis or paraneoplastic limbic encephalitis. We report a case of neurosyphilis with mesiotemporal involvement on MRI. Positive antibodies in the cerebrospinal fluid confirmed the diagnosis. The results suggest that neurosyphilis should be considered when MRI results indicate mesiotemporal abnormalities.

Worsened MRI findings during the early period of treatment with penicillin in a patient with general paresis

A 52-year-old man was diagnosed with general paresis, whose HIV antibodies were negative. After initiation of treatment with penicillin on the first day, no obvious clinical Jarisch-Herxheimer reaction was found. However, 6 days after treatment, the patient was found more irritable and was unable to fall asleep at night. On the seventh day, worsened magnetic resonance imaging (MRI) abnormalities in the bilateral medial and anterior temporal lobes were unexpectedly discovered. These worsened MRI abnormalities improved quickly after the addition of dexamethasone treatment. We consider that these transient and slight mental symptoms may be associated with the transiently worsening phenomenon in cerebral MRI findings during the early period of treatment with penicillin. This indicates that some nonspecific inflammatory process has happened in the early stage of treatment, which necessitates the use of corticosteroids after the occurrence of systemic or mental symptoms.

Central nervous system infections of herpesvirus family

Herpesviruses are one of the most common groups of pathogens causing central nervous system infections in humans. They mostly cause encephalitis, meningitis, or myelitis in immunocompetent and immunocompromised patients. Children, adults, and the elderly can all be affected. Although contrast-enhanced CT is more widely used for diagnosis, contrast-enhanced MR imaging combined with diffusion-weighted imaging is superior to CT in the detection of early changes and the real extent of the disease, and in assessing prognosis and monitoring response to antiviral treatment. More sophisticated techniques, such as MR spectroscopy and perfusion imaging, can aid in the differential diagnosis of herpesvirus infections from other tumoral, demyelinating, and ischemic processes.

CSF findings in patients with voltage gated potassium channel antibody associated limbic encephalitis

Recently, a new subtype of limbic encephalitis (LE) has been described, serologically characterized by the presence of antibodies against voltage gated potassium channels (VGKC, to be called VGKC-LE). Only little is known about CSF findings in this new disorder. Here we report the results of 29 lumbar punctures in 17 patients with VGKC-LE. Slight pleocytosis, mainly consisting of lymphocytes and monocytes, and elevated total protein concentrations were present in 41 and 47%, respectively. Intrathecal immunoglobulin (Ig) synthesis as defined by the presence of CSF-specific oligoclonal IgG bands, an increased IgG index, or an elevated IgG, IgA, or IgM ratio, was not detected in any of the patients, but dysfunction of the blood-CSF barrier was found in 35%. CSF findings were normal in 23%.

CONCLUSIONS

Unlike paraneoplastic LE, VGKC-LE is not frequently associated with intrathecal Ig production or markedly elevated white cell counts. Thus, normal CSF findings do not preclude the disease. VGKC-Ab should, therefore, be determined whenever LE is clinically suspected, irrespective of the presence or absence of inflammatory CSF changes.

Neurosyphilis with mesiotemporal magnetic resonance imaging abnormalities

We describe a patient with mesial temporal T2-weighted image hyperintensity on magnetic resonance imaging that mimicked paraneoplastic limbic encephalitis. The patient showed pupillary abnormalities suggestive of a diagnosis of neurosyphilis, and the diagnosis was supported by the results of a serum Treponema pallidum hemagglutination assay (TPHA) and cerebrospinal fluid examination. Making a diagnosis of neurosyphilis is occasionally difficult because of the variety of clinical and imaging findings. Appropriate diagnosis and commencing adequate treatment are needed for a good prognosis; thus, neurosyphilis should be included in the differential diagnosis of mesiotemporal magnetic resonance imaging abnormalities.

Limbic encephalitis: a cause of temporal lobe epilepsy with onset in adult life

Limbic encephalitis (LE) was described in the 1960s as a clinical-pathological syndrome in adults. Initially, the paraneoplastic form was the center of interest. An increasing number of diagnostically valuable autoantibodies in patients' sera (and cerebrospinal fluid) have been identified. Lately, the impact of non-paraneoplastic LE cases has been acknowledged. In the serum of some of these patients, antibodies against voltage-dependent potassium channels (VGKC antibodies) have been detected. The characteristic MRI course of LE patients has recently been described in detail: hippocampal swelling and T2/FLAIR signal increase are early findings. After a few months, the swelling regresses, followed by hippocampal atrophy with continuous signal increase. A general consensus on formal diagnostic criteria for all LE subsyndromes has not yet been reached. This article proposes such diagnostic criteria and formulates suggestions for treatment.

Neuropsychological symptoms in paraneoplastic disorders

Neuropsychological symptoms may rarely be part of a paraneoplastic neurological syndrome, mainly as limbic encephalitis. As the tumour will not be known in most patients upon presentation to the neurologists, state-of-the art diagnosis including the use of anti-neuronal antibodies and FDG-PET is essential for adequate management of these patients.

[Potentially reversible dementia]

Reversible dementia is rare and accounts for approximately 1.5% of all dementias. Systematic ancillary investigations aimed at detecting an infectious disease, an endocrine aetiology or a vitamin deficiency are rarely contributive, but remain relevant since reversible dementia may, very rarely, mimic Alzheimer-type dementia. Aetiological investigations are much better selected and contributory when they rely on a precise analysis of the clinical picture (past medical history, age of the patient, cognitive, psychiatric and behavioural symptoms, type of onset, and associated signs) and of cerebral imaging. Discovering a reversible cause of dementia does not always mean that the patient will completely recover; thus it is more appropriate to use the term "potentially reversible dementia". Finally, when the patient does not recover from dementia, systematic ancillary investigations can identify and treat concomitant reversible conditions, which in nearly 25% of dementia cases contribute to worsening the condition.

Serial MRI of limbic encephalitis

INTRODUCTION

The aim of the study was to analyze serial magnetic resonance imaging (MRI) scans in patients with various forms of limbic encephalitis (LE) in order to evaluate whether, and at what time point, MRI findings support the diagnosis of LE.

METHODS

Serial MRI scans (1 day to 15 years after the onset of symptoms) of 20 patients with LE were retrospectively evaluated. Of these 20 patients, 16 had definite LE (histopathological limbic inflammation, n=6; onconeural antibodies, n=5; voltage-gated potassium channel antibodies, n=3; malignant tumors, n=5), and 4 possible LE because they met the clinical criteria but had no typical antibodies or tumors.

RESULTS

Of 13 patients who were studied with MRI within 3 months after the onset of symptoms, 11 had swollen temporomesial structures (unilateral, n=7; bilateral, n=4). After up to 9 months, the swelling had resolved in nine of ten re-evaluated patients. Of seven patients who were initially studied with MRI more than 3 months after disease onset, three had swollen temporomesial structures, one had a hyperintense, normal-sized hippocampus, and three had hyperintense and atrophic temporomesial structures.

CONCLUSION

LE starts as an acute disease with uni- or bilateral swollen temporomesial structures that are hyperintense on fluid attenuation inversion recovery and T2-weighted sequences. Swelling and hyperintensity may persist over months to years, but in most cases progressive temporomesial atrophy develops.