Neuroimaging observations linking neurocysticercosis and mesial temporal lobe epilepsy with hippocampal sclerosis

Neurocysticercosis-related Seizures: Imaging Biomarkers

Neurocysticercosis (NCC)-a parasitic CNS infection endemic to developing nations-has been called the leading global cause of acquired epilepsy yet remains understudied. It is currently unknown why a large proportion of patients develop recurrent seizures, often following the presentation of acute seizures. Furthermore, the presentation of NCC is heterogenous and the features that predispose to the development of an epileptogenic state remain uncertain. Perilesional factors (such as oedema and gliosis) have been implicated in NCC-related ictogenesis, but the effects of cystic factors, including lesion load and location, seem not to play a role in the development of habitual epilepsy. In addition, the cytotoxic consequences of the cyst's degenerative stages are varied and the majority of research, relying on retrospective data, lacks the necessary specificity to distinguish between acute symptomatic and unprovoked seizures. Previous research has established that epileptogenesis can be the consequence of abnormal network connectivity, and some imaging studies have suggested that a causative link may exist between NCC and aberrant network organisation. In wider epilepsy research, network approaches have been widely adopted; studies benefiting predominantly from the rich, multimodal data provided by advanced MRI methods are at the forefront of the field. Quantitative MRI approaches have the potential to elucidate the lesser-understood epileptogenic mechanisms of NCC. This review will summarise the current understanding of the relationship between NCC and epilepsy, with a focus on MRI methodologies. In addition, network neuroscience approaches with putative value will be highlighted, drawing from current imaging trends in epilepsy research.

Evaluating the Association of Calcified Neurocysticercosis and Mesial Temporal Lobe Epilepsy With Hippocampal Sclerosis in a Large Cohort of Patients With Epilepsy

Background

Neurocysticercosis (NCC) is a parasitic infection of the central nervous system that has been associated with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). However, this association has not been completely established.

Objective

To evaluate the prevalence of calcified NCC (cNCC), its characteristics and a possible association between cNCC and MTLE-HS in a cohort of 731 patients with epilepsy.

Methods

We review clinical, EEG and neuroimaging findings of 731 patients with epilepsy. From these, 659 had CT-scans and 441 patients had complete neuroimaging with CT-scans and MRI. In these patients, we review the prevalence and characteristic of epilepsy in cNCC and in MTLE-HS patients.

Results

Forty-two (6.4%) of the 659 patients studied with CT-scans had cNCC. cNCC lesions were more frequent in women than in men (n = 33–78.6% vs. n = 09–21.4%, respectively; OR = 3.64;(95%CI = 1.71–7.69); p < 0.001). cNCC was more often in patients who developed epilepsy later in life, in older patients, in patients who had a longer history of epilepsy, and in those with a lower educational level. MTLE–HS was observed in 93 (21.1%) of 441 patients that had complete neuroimaging, and 25 (26.9%) of these 93 patients also had cNCC. Calcified NCC was observed in only 17 (4.9%) of the remaining 348 patients that had other types of epilepsy rather than MTLE-HS. Thus, in our cohort, cNCC was more frequently associated with MTLE-HS than with other forms of epilepsy, O.R. = 11.90;(95%CI = 6.10–23.26); p < 0.0001).

Conclusions

As expected, in some patients the epilepsy was directly related to cNCC lesional zone, although this was observed in a surprisingly lower number of patients. Also, cNCC lesions were observed in other forms of epilepsy, a finding that could occur only by chance, with epilepsy probably being not related to cNCC at all. In this cohort, cNCC was very commonly associated with MTLE-HS, an observation in agreement with the hypothesis that NCC can contribute to or directly cause MTLE-HS in many patients. Given the broad world prevalence of NCC and the relatively few studies in this field, our findings add more data suggesting a possible and intriguing frequent interplay between NCC and MTLE-HS, two of the most common causes of focal epilepsy worldwide.

Changes in inflammatory gene expression in brain tissue adjacent and distant to a viable cyst in a rat model for neurocysticercosis

BACKGROUND

The parasite Taenia solium causes neurocysticercosis (NCC) in humans and is a common cause of adult-onset epilepsy in the developing world. Hippocampal atrophy, which occurs far from the cyst, is an emerging new complication of NCC. Evaluation of molecular pathways in brain regions close to and distant from the cyst could offer insight into this pathology.

METHODS

Rats were inoculated intracranially with T. solium oncospheres. After 4 months, RNA was extracted from brain tissue samples in rats with NCC and uninfected controls, and cDNA was generated. Expression of 38 genes related to different molecular pathways involved in the inflammatory response and healing was assessed by RT-PCR array.

RESULTS

Inflammatory cytokines IFN-γ, TNF-α, and IL-1, together with TGF-β and ARG-1, were overexpressed in tissue close to the parasite compared to non-infected tissue. Genes for IL-1A, CSF-1, FN-1, COL-3A1, and MMP-2 were overexpressed in contralateral tissue compared to non-infected tissue.

CONCLUSIONS

The viable cysticerci in the rat model for NCC is characterized by increased expression of genes associated with a proinflammatory response and fibrosis-related proteins, which may mediate the chronic state of infection. These pathways appear to influence regions far from the cyst, which may explain the emerging association between NCC and hippocampal atrophy.

Epilepsy outcomes and hippocampal volumes in children with multiple parenchymal neurocysticercoses

Background:

We aimed to study the radiological and epilepsy outcomes of children with multiple neurocysticercosis (NCC) and the relationship with hippocampus volume.

Study Design:

Observational study.

Materials and Methods:

Children between 5 and 18 years of age with NCC lesions and completed more than 2-year follow-up were enrolled. Magnetic resonance imaging (MRI) brain with a predefined protocol was done as per clinical indication, and bilateral hippocampi volume was measured with a region of interest-based manual method. Proportion of children who had radiological resolution of lesions, proportion of children who were seizure-free for at least 3 months after antiepileptic drugs withdrawal, and mean hippocampi volume were calculated.

Results:

During the study period, 229 children followed up in pediatric NCC clinic were enrolled, the mean age was 10.5 ± 3 years, and 129 (56%) were boys. A total of 159 (65%) children had single-lesion NCC, and 79 (35%) had multiple lesion (> 2) NCC. Resolution of lesions was seen in 8% children with multiple NCC, significantly less as compared to the single NCC group (8% vs. 27%, P = 0.006). Multiple-lesion NCC group had a higher rate of calcification as compared to children with a single lesion (66% vs. 47%, P = 0.008). Twenty-nine (37%) children with multiple-lesion NCC were seizure free for at least 3 months after antiepileptic drug withdrawal. Mean combined hippocampal volume in children with single-lesion NCC was 2.96 (0.62) mL and multiple-lesion NCC was 2.88(0.43) mL.

Conclusion:

Children with multiple-lesion NCC have lower resolution, and higher calcification during follow-up in comparison to single-lesion NCC. Frequency of children who remained seizure-free 3-month post AED withdrawal was similar in single- and multiple-lesion groups.

Dual/double pathology in neurocysticercosis causing drug resistant epilepsy - Chance association or causal?

INTRODUCTION

Neurocysticercosis (NCC) as cause of drug resistant epilepsy (DRE) is commonly reported from India. We reviewed the neuropathological findings in patients undergoing resective surgery for DRE due to NCC, to determine the pathomechanism of epileptogenesis.

METHODS

Clinical, demographic and neuropathological findings of histologically confirmed cases of NCC causing DRE between 2005-2019 were reviewed. NeuN, GFAP, phosphorylated neurofilament, vimentin, CD34 for glial/ neuronal alterations, and Masson trichrome, Luxol Fast blue for evidence of fibrosis/ demyelination was used to determine cause of epileptogenesis.

RESULTS

There were 12 cases of NCC associated with dual/ double pathology, which constituted 3.02 % (12/398) of all the operated DRE. [Age range: 17-37y, Male:Female = 1.4:1]. Seizure duration ranged from 3-32y, with seizure onset between 4-27y. On MRI, lesions were of variable signal intensity on T1 and isointense on T2 with blooming on GRE/ SWI, and CT revealed calcification. Majority (11/12) had associated hippocampal sclerosis (HS) type 1 (dual pathology), localised to the same side as cysticercal cyst, suggesting it may be involved in the pathogenesis of HS. Ten had single cysticercal lesion involving ipsilateral hippocampus in 6, parahippocampal gyrus in 2, amygdala and temporal lobe in 1 case each. One had multiple NCC located in bilateral frontal, parietal and ipsilateral hippocampus. Adjacent cortex around the NCC evaluated in 6 cases, revealed inflammation, gliosis, axonal disruption/ beading, and variable synaptic/ neuronal dystrophic changes. There was a single case of NCC with Focal cortical dysplasia (FCD) type IIb (double pathology). In 11/12 cases Engel's post-surgery outcome was available with all having class I outcome.

CONCLUSION

HS was most common pathology associated with cysticercosis (Dual pathology), localised ipsilateral to the cysticercal cyst, suggesting that HS is a secondary/ epiphenomenon. Perilesional changes such as inflammation, gliosis, dystrophic synaptic and axonal pathology play a role in inducing or perpetuating the epileptiform activity. The association of FCD IIb with NCC in one case is likely to be a chance occurrence.

Taenia solium Cysticercosis and Its Impact in Neurological Disease

Taenia solium neurocysticercosis (NCC) is endemic in most of the world and contributes significantly to the burden of epilepsy and other neurological morbidity. Also present in developed countries because of immigration and travel, NCC is one of few diseases targeted for eradication. This paper reviews all aspects of its life cycle (taeniasis, porcine cysticercosis, human cysticercosis), with a focus on recent advances in its diagnosis, management, and control. Diagnosis of taeniasis is limited by poor availability of immunological or molecular assays. Diagnosis of NCC rests on neuroimaging findings, supported by serological assays. The treatment of NCC should be approached in the context of the particular type of infection (intra- or extraparenchymal; number, location, and stage of lesions) and has evolved toward combined symptomatic and antiparasitic management, with particular attention to modulating inflammation. Research on NCC and particularly the use of recently available genome data and animal models of infection should help to elucidate mechanisms of brain inflammation, damage, and epileptogenesis.

Unique Characteristics of Epilepsy Development in Neurocysticercosis

The parasitic helminth infection neurocysticercosis (NCC) is the most common cause of adult-acquired epilepsy in the world. Despite the serious consequences of epilepsy due to this infection, an in-depth review of the distinct characteristics of epilepsy due to neurocysticercosis has never been conducted. In this review, we evaluate the relationship between NCC and epilepsy and the unique characteristics of epilepsy caused by NCC. We also discuss recent advances in our understanding of NCC-related epilepsy, including the importance of anti-inflammatory therapies, the association between NCC and temporal lobe epilepsy, and the recent discovery of biomarkers of severe epilepsy development in individuals with NCC and seizures.

Neurocysticercosis as a probable risk factor for hippocampal sclerosis

ABSTRACT Neurocysticercosis is one of the most common risk factors for epilepsy but its association with drug-resistant epilepsy remains uncertain. Conjectures of an association with drug-resistant epilepsy have been fueled by reports of an association between calcific neurocysticercosis lesions (CNL) and hippocampal sclerosis (HS) from specialized epilepsy centers in Taenia solium-endemic regions. The debate arising from these reports is whether the association is causal. Evidence for the association is not high quality but sufficiently persuasive to merit further investigation with longitudinal imaging studies in population-based samples from geographically-diverse regions. The other controversial point is the choice of a surgical approach for drug-resistant epilepsy associated with CNL-HS. Three approaches have been described: standard anteromesial temporal lobectomy, lesionectomy involving a CNL alone and lesionectomy with anteromesial temporal lobectomy (for dual pathology); reports of the latter two approaches are limited. Presurgical evaluation should consider possibilities of delineating the epileptogenic zone/s in accordance with all three approaches.

EEG Patterns in Patients With Calcified Neurocysticercosis With or Without Hippocampal Atrophy

PURPOSE

To assess whether hippocampal atrophy develops in conjunction with clinical or subclinical epileptiform or encephalopathic activity in subjects with neurocysticercosis (NCC).

METHODS

Using a population-based and nested case-control study design, scalp EEGs and brain MRIs were performed in Atahualpa residents aged ≥40 years, who have imaging-confirmed NCC (case patients), as well as in age- and sex-matched NCC-free control subjects.

RESULTS

Sixty-two case patients and 62 control subjects were included. Encephalopathic EEG patterns were more common in five NCC subjects with epilepsy than in those without a history of seizures. Epileptiform EEG activity was noted in one patient with NCC but in none of the control subjects. This subject's focal epileptiform discharges correlated with the location of calcified cysticerci in the brain parenchyma, and the hippocampus ipsilateral to the epileptiform discharges was more atrophic than the contralateral hippocampus. The degree of hippocampal atrophy in patients with NCC without a history of seizures was significantly greater than in control subjects (P < 0.01) and tended to be even greater in patients with NCC with a history of seizures.

CONCLUSIONS

Hippocampal atrophy may not be exclusively related to seizure activity in patients with NCC. Other mechanisms, such as recurrent bouts of inflammation around calcified cysticerci, might explain the association between NCC and hippocampal atrophy.

Hippocampal sclerosis induced in mice by a Taenia crassiceps metacestode factor

An experimental Taenia crassiceps mouse model was used to assess the role of Taenia solium metacestode factor (Fac) in human neurocysticercosis. Intraperitoneal infection with T. crassiceps metacestodes or subcutaneous inoculation with a T. crassiceps metacestode factor (Fac) produced significant impairment of performance (learning) in the Barnes maze and induced bilateral hippocampal sclerosis in mice. Several staining techniques revealed important cell dispersion, extensive apoptosis and cell loss in the dentate gyrus, hilus and CA1-CA3 regions of both hippocampi, as well as intense deterioration of the adjacent cortex. An outstanding disruption of its histoarchitecture in the surrounding tissue of all these regions and apoptosis of the endothelial cells were also observed.

Clinical topography relationship in patients with parenchymal neurocysticercosis and seizures

OBJECTIVE

Discordances between imaging findings of parenchymal neurocysticercosis and seizure expression have been reported, and as such the possibility that neurocysticercosis and seizures may frequently coexist by chance has been raised. In this study, we evaluate the topographic relationship between seizure foci based on semiology and electroencephalography with the location of parenchymal neurocysticercotic lesions.

METHODS

Seizure information, neuroimaging (computed tomography and magnetic resonance imaging [MRI]) and electroencephalographic data from three randomized clinical trials of individuals with parenchymal neurocysticercosis and focal seizures were analyzed. Blinded epileptologists defined a potential seizure onset zone and a symptomatogenic zone for each individual based on semiology. The topographic relationship between semiology, either lesion location or areas of perilesional edema on baseline MRI, and electroencephalographic abnormalities were assessed.

RESULTS

Fifty-eight patients with one or two parenchymal neurocysticercotic lesions were included in this study. From them, 50 patients (86%; 95% CI, 75%-93%) showed a clinical-topography relationship with the potential seizure onset zone, and 44 (76%) also with the symptomatogenic zone. From the eight patients with no topographic relationship, five had focal seizures 30 days before or after the baseline MRI and showed perilesional edema. All of these five patients showed a clinical-topography relationship between such seizures and an area of perilesional edema, making a total of 55 patients (95%; 95% CI, 85%-99%) with clinical-topography relationship when perilesional edema is considered. Most patients with focal epileptiform discharges (7/8, 88%) had a topographic association between electroencephalographic focality, the potential seizure onset zone and a cysticercotic lesion.

CONCLUSION

Seizure semiology and focal epileptiform discharges are topographically related to neurocysticercotic lesions in most patients. These data strongly support seizure origin in the cortex surrounding these lesions.

Clinical presentation of neurocysticercosis-related epilepsy

Neurocysticercosis (NCC) is the most common parasitic infection of the central nervous system and a major risk factor for seizures and epilepsy. Seizure types in NCC vary largely across studies and seizure semiology is poorly understood. We discuss here the studies regarding seizure types and seizure semiology in NCC, and examine the clinical presentation in patients with NCC and drug-resistant epilepsy. We also provide evidence of the role of MRI and EEG in the diagnosis of NCC-related epilepsy. Focal seizures are reported in 60-90% of patients with NCC-related epilepsy, and around 90% of all seizures registered prospectively are focal not evolving to bilateral tonic-clonic seizures. A great number of cases suggest that seizure semiology is topographically related to NCC lesions. Patients with hippocampal sclerosis and NCC have different clinical and neurophysiological characteristics than those with hippocampal sclerosis alone. Different MRI protocols have allowed to better differentiate NCC from other etiologies. Lesions' stages might account on the chances of finding an interictal epileptiform discharge. Studies pursuing the seizure onset in patients with NCC are lacking and they are specially needed to determine both whether the reported events of individual cases are seizures, and whether they are related to the NCC lesion or lesions. This article is part of a Special Issue entitled "Neurocysticercosis and Epilepsy".

Antiparasitic treatment of neurocysticercosis - The effect of cyst destruction in seizure evolution

Antiparasitic agents against Taenia solium cysticercosis have been in use since 1979, although its use has been questioned on the basis that cysts would die naturally and thus treatment-induced inflammation is unnecessary. In addition, isolated reports have also questioned whether neurocysticercosis (NCC) is a cause of epilepsy. After more than three and a half decades, a large body of evidence is available. Little if any doubt exists about NCC as a cause of seizures - NCC is consistently associated with seizures when appropriate groups are compared, and in a large subset of cases, seizure semiology correlates with the anatomical location of lesions. Cyst degeneration and the subsequent inflammatory reaction increase seizure expression, although patients with non-inflamed cysts may have seizures, as do patients with long-standing, not inflamed calcified scars. Assessment of the evidence on cysticidal efficacy, safety, and the impact of cyst destruction in decreasing seizures leads to the conclusion that the benefits of antiparasitic treatment in parenchymal brain cysticercosis clearly outweigh the risks, and have provided substantive evidence of the role of NCC as a cause of seizures and epilepsy. Antiparasitic therapy should be considered a primary option in the management of patients with live or degenerating brain NCC cysts. This article is part of a Special Issue entitled "Neurocysticercosis and Epilepsy".

Understanding the association of neurocysticercosis and mesial temporal lobe epilepsy and its impact on the surgical treatment of patients with drug-resistant epilepsy

Mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS) is one of the most common types of focal epilepsies. This is an epileptic syndrome commonly associated with treatment-resistant seizures, being also the most prevalent form of drug-resistant epilepsy which is treated surgically in most epilepsy surgery centers. Neurocysticercosis (NCC) is one of the most common parasitic infections of the central nervous system, and one of the most common etiological agents of focal epilepsy, affecting millions of patients worldwide. Recently, researchers reported a curious association between MTLE-HS with NCC, but this association remains poorly understood. Some argue that calcified NCC lesions in MTLE-HS patients is only a coincidental finding, since both disorders are prevalent worldwide. However, others suppose there might exist a pathogenic relationship between both disorders and some even suspect that NCC, by acting as an initial precipitating injury (IPI), might cause hippocampal damage and, eventually, MTLE-HS. In this review, we discuss the various reports that examine this association, and suggest possible explanations for why calcified NCC lesions are also observed in patients with MTLE-HS. We also propose mechanisms by which NCC could lead to MTLE-HS. Finally, we discuss the implications of NCC for the treatment of pharmacologically-resistant focal epilepsies in patients with calcified NCC or in patients with MTLE-HS and calcified NCC lesions. We believe that investigations in the relationship between NCC and MTLE-HS might offer further insights into how NCC may trigger epilepsy, and into how MTLE-HS originates. Moreover, observations in patients with drug-resistant epilepsy with both NCC and hippocampal sclerosis may not only aid in the understanding and treatment of patients with MTLE-HS, but also of patients with other forms of dual pathologies aside from NCC. This article is part of a Special Issue titled Neurocysticercosis and Epilepsy.

Natural History of Patients With Perilesional Edema Around Taenia solium Calcified Granulomas

Background

The transient development of perilesional edema (PE) around ≥1 calcification (defined as 1 episode) occurs in about 50% of the patients with recurrent seizures in calcified neurocysticercosis (NCC). We determined the long-term clinical and radiological course of persons undergoing PE episodes.

Methods

Twenty-one persons with NCC who experienced ≥1 PE episode were followed for a median of 10.6 years (range, 0.4-29.2 years). Clinical evaluations and magnetic resonance imaging (MRI) were performed at the time of suggestive symptoms and during routine follow-up.

Results

PE episodes were documented 78 times, involving 50 of 729 calcifications. Episodes reoccurred in all but 3 persons. The pattern, rate, and number of episodes were variable, commonly chronic, and not significantly associated with time from treatment, number of calcifications, or sex. Seizure was the most common symptom, but almost 30% of episodes were asymptomatic and detected by MRI during routine follow-up. Persons with delayed recurrent episodes were significantly older (age, 42.3 vs 28.8 years; P = .045). Seizures continued to occur in 37.5%, and 2 persons had a severe disabling clinical course.

Conclusions

The number and timing of PE episodes in individuals with calcified NCC are variable and commonly chronic, sometimes recurring over decades. A minority of patients developed significant disability.

Pathogenesis of Taenia solium taeniasis and cysticercosis

Taenia solium infections (taeniasis/cysticercosis) are a major scourge to most developing countries. Neurocysticercosis, the infection of the human nervous system by the cystic larvae of this parasite, has a protean array of clinical manifestations varying from entirely asymptomatic infections to aggressive, lethal courses. The diversity of clinical manifestations reflects a series of contributing factors which include the number, size and location of the invading parasites, and particularly the inflammatory response of the host. This manuscript reviews the different presentations of T. solium infections in the human host with a focus on the mechanisms or processes responsible for their clinical expression.

Update on the Diagnosis and Management of Neurocysticercosis

Neurocysticercosis is an important cause of seizures worldwide and is endemic in most of Latin America, Sub-Saharan Africa, Southeast Asia, India, and China. Neurocysticercosis has profoundly different disease manifestations varying from asymptomatic presentation to life-threatening hydrocephalus. Clinical manifestations, pathogenesis, diagnostic methods, and optimal treatment vary with the location, number of lesions, and host response. Diagnosis is based on a combination of clinical presentation, neuroimaging findings, history of exposure, and serologic testing. Initial therapy should be focused on symptom management including seizure control and management of increased intracranial pressure. Emerging data are demonstrating that the optimal management approach varies with stage. Single enhancing or cystic lesions should be treated with albendazole and steroids. Patients with more than two cystic lesions should be treated with combination therapy with albendazole and praziquantel, whereas patients with hydrocephalus benefit from surgical management, especially with minimally invasive approaches.