The Association Between Neurocysticercosis and Hippocampal Atrophy is Related to Age

Current challenges in neurocysticercosis: recent data and where we are heading

PURPOSE OF REVIEW

Neurocysticercosis (NCC) is still a significant contributor to neurological disease in vast regions of the world, and increasingly diagnosed in nonendemic countries because of travel and immigration from endemic settings. There is a need for clinicians in endemic and nonendemic regions to understand the complexities of its diagnosis and management.

RECENT FINDINGS

Recent information on the performance and use of available imaging and immunodiagnostic tools as well as antiparasitic and anti-inflammatory therapeutic regimes were assessed.

SUMMARY

Imaging and serology data should be assessed in the context of the specific type of NCC to improve diagnostic precision. In terms of therapeutic approaches, more controlled data is required on the efficacy and safety of combined antiparasitic therapy, and antiseizure and anti-inflammatory regimes should be optimized to minimize perilesional damage and reduce the risk of epilepsy.

Management of calcified cysticerci in the brain parenchyma: treating the dead parasite

INTRODUCTION

Calcifications are the end stage of many parenchymal brain cysticerci and may occur either spontaneously or as the result of treatment with cysticidal drugs. These lesions, traditionally considered inert and asymptomatic, have been associated with several complications that seem to be mostly related to brain damage and inflammation ensuing as the result of the exposure of the host's immune system to parasitic antigens trapped within calcifications.

AREAS COVERED

This review, based on the search of different electronic databases up to May 2024, focuses on the reported correlates and complications of calcified cysticerci (chronic headaches, seizures/epilepsy, hippocampal atrophy/sclerosis, gliomas), and the different interventions developed for their prevention and treatment. Common analgesics, non-steroidal anti-inflammatory drugs, corticosteroids, and antiseizure medications have been used with success but, with the exception of the latter, these drugs offer temporary relief of symptoms and support for their use is based on level 3 evidence.

EXPERT OPINION

Several strategies may reduce the severity of clinical consequences of calcified cysticerci. Probably, the most relevant intervention would be the prevention of their occurrence or reduction in their size. In this view, the use of bisphosphonates appears as a potential option that needs to be tested in humans.

Large (≥3-Millimeter) Parenchymal Brain Calcified Cysticerci Are More Often Associated with Hippocampal Atrophy than Smaller Ones in Seizure-Free Individuals with a Single Lesion

Calcified cysticerci are often associated with hippocampal atrophy (HA). While most studies suggest that repetitive seizures cause HA in these patients, others have demonstrated that HA may also occur in persons without epilepsy. Little is known about mechanisms triggering HA in seizure-free individuals with calcified cysticerci. Here, we aimed to assess whether the size of the calcification is associated with HA. Using a population-based design, we selected apparently seizure-free individuals with a single calcified cysticercus in whom interictal paroxysmal activity and other causes of HA have been discarded. A total of 55 individuals (mean age, 58.3 ± 13 years, 62% women) fulfilled inclusion criteria. Unadjusted and multivariate models were fitted to assess the association between the size of the calcification dichotomized into <3 mm and ≥3 mm (exposure) and the presence of HA (outcome). Sixteen participants (29%) had HA, which was asymmetric in eight (50%) cases. Hippocampal atrophy was noted in 11/20 (55%) participants with large calcifications and in 5/35 (14%) with small calcifications (P = 0.001). A multivariate logistic regression model showed a significant association between the presence of large calcifications and HA, after adjustment for relevant confounders (odds ratio: 7.78; 95% CI: 1.72-35.1). Participants with calcifications ≥3 mm in diameter were 7.8 times more likely to have HA than those with smaller ones. Study results open avenues of research for the use of agents to prevent HA progression.

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.

Hippocampal Atrophy/Sclerosis Is Associated with Old, Calcified Parenchymal Brain Neurocysticercosis, But Not with More Recent, Viable Infections

Magnetic resonance images from 197 patients with calcified neurocysticercosis (NCC), 38 with viable NCC and 197 NCC-free healthy rural villagers were evaluated to compare the frequency of hippocampal atrophy/sclerosis (HAS) across these populations. Scheltens' medial temporal atrophy scale was used for hippocampal rating. The median age of the 432 study participants was 46 years (interquartile range, 29-62 years), and 58% were women. Hippocampal atrophy/sclerosis was disclosed in 26.9% patients with calcified NCC, compared with 7.9% in patients with viable NCC and 8.1% in healthy rural villagers. After adjusting for age, gender, and history of epilepsy, hippocampal atrophy/sclerosis was more frequent in patients with calcified NCC than in those with viable cysts (RR, 3.60; 95% CI, 1.18- 0.99; P = 0.025) and healthy rural villagers (RR, 3.43; 95% CI, 1.94-6.06; P < 0.001), suggesting that hippocampal damage develops late in the course of this parasitic disease.

Brain calcification because of neurocysticercosis: a vast field to be explored

PURPOSE OF REVIEW

Neurocysticercosis is the most common helminthic infection of the central nervous system caused by the larval stage of the pork tapeworm, Taenia solium. Endemic regions include Latin American countries, sub-Saharan Africa, and large regions of Asia, including the Indian subcontinent and is a global health problem. Seizures are the most common manifestation and approximately 30% of adult-onset seizures in endemic regions are attributable to NCC. Calcifications because of neurocysticercosis is the most common finding on imaging in endemic regions and are important seizure foci contributing to the burden of epilepsy.

RECENT FINDINGS

After treatment with antiparasitics for multiple viable parenchymal disease, approximately 38% of cysts that resolved after 6 months of therapy will result in residual calcifications, which represents a significant burden of residual disease. Calcified disease has been referred to as 'inactive disease', but there is accumulating evidence to suggest that calcified granulomas are actually dynamic and substantially contribute to the development and maintenance of seizures.

SUMMARY

Calcified parenchymal neurocysticercosis contributes significantly to the development and maintenance of seizures in endemic regions. Understanding the pathogenesis of the role of calcified NCC in seizure development and risk factors for development of calcifications after treatment is critical to decreasing the burden of symptomatic disease in endemic regions.

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.

An Ambispective Cohort Study to Assess Seizure Recurrences in Children with Calcified Parenchymal Neurocysticercosis

Calcified neurocysticercosis (NCC), previously thought to be a dead end, is an important risk factor for seizure recurrences. We studied the pattern of seizure recurrences and associated radiological findings in children with calcified NCC. In this ambispective cohort study, we enrolled children (age 1-15 years) with calcified NCC attending the pediatric NCC clinic between January 2017 and December 2017. Retrospective data were collected from the hospital records, and all enrolled children were prospectively followed up till June 2018. The study group divided into two groups: 1) children first presenting with calcified granuloma and 2) children presented with ring-enhancing lesion (REL) and transformed into the calcified lesion during follow-up imaging. During the study period (January 2017-December 2017), 520 children with NCC were screened and 128 with calcified NCC were enrolled. The mean age was 10.8 ± 3.2 years, and 63% were boys. Among 128 children, 40 (31%) had calcified granuloma and 88 (69%) had REL transformed to calcified granuloma. Sixty-one (49%) children had seizure recurrence: 22 (58%) within calcified granuloma group and 39 (45%) within REL transformed to calcified granuloma group (P = 0.18). Seizure recurrence was associated with the presence of perilesional edema (PE) in 35 (57.4%) children on computed tomography scan. The median interval between two seizure recurrences was 30 (17-56) months, and the median antiepileptic drug-free interval was 17 (12-22) months. The total duration of continued seizures was 42 (26-58) months, slightly longer in children with REL transformed to calcified granuloma group (42, 95% CI: 18-66 months) in comparison to calcified granuloma group (35, 95% CI: 10-60 months, P = 0.32). To conclude, children with calcified NCC have seizure recurrences over a prolonged period. Seizure recurrences are intermittent and may be interspersed with a prolonged period of quiescence in between. The presence of PE and contrast enhancement around the lesion during seizure recurrence suggests lesion reactivation.

The Association between Calcified Neurocysticercosis and Cognitive Performance: A Case-Control Study Nested to a Population-Based Cohort

Mechanisms implicated in the association between neurocysticercosis (NCC) and cognitive impairment remain unknown. Atahualpa residents aged ≥ 40 years with calcified NCC were identified as case patients and paired 1:1 to age- and gender-matched controls. The selection process generated 79 pairs. Cognitive performance was measured by the Montreal Cognitive Assessment (MoCA). A conditional logistic regression model revealed no differences in MoCA scores across case patients and controls, after adjusting for education, epilepsy, depression, and hippocampal atrophy. The single covariate remaining significant was hippocampal atrophy. When participants were stratified according to this covariate, linear models showed lower MoCA scores among case patients (but not controls) with hippocampal atrophy. In a fully adjusted linear regression model, age remained as the single covariate explaining cognitive impairment among NCC patients. This study demonstrates an association between hippocampal atrophy and poor cognitive performance among patients with calcified NCC, most likely attributable to the effect of age.

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.

Spontaneously Arrested Transmission of Cysticercosis in a Highly Endemic Village with a Very Low Migration Rate

Taenia solium cysticercosis is difficult to eliminate without interventions or societal development. Atahualpa is a rural Ecuadorian village with documented low migration rate, where domestic pig raising is common and human cysticercosis is endemic. To assess neurocysticercosis (NCC) prevalence, 1,273 villagers aged ≥ 20 years underwent neuroimaging studies, which showed calcified lesions in 121 (9.5%) individuals, but no active disease. Likewise, positive reactions, apparently nonspecific, were found in only 3/200 subjects by the use of a monoclonal antibody-based enzyme-linked immunosorbent assay to detect T. solium antigens in urine. Only 2/418 pigs reacted to three antibody bands on serum western blot and none to more than three bands. This is the first time that spontaneously arrested T. solium transmission is documented in a known endemic village. Understanding why active transmission stopped could provide insights on potential targets for control interventions. Atahualpa could provide an optimal scenario for longitudinal studies on the consequences of calcified NCC.

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".

On the relationship between calcified neurocysticercosis and epilepsy in an endemic village: A large-scale, computed tomography-based population study in rural Ecuador

OBJECTIVE

Using a large-scale population-based study, we aimed to assess prevalence and patterns of presentation of neurocysticercosis (NCC) and its relationship with epilepsy in community-dwellers aged ≥20 years living in Atahualpa (rural Ecuador).

METHODS

In a three-phase epidemiological study, individuals with suspected seizures were identified during a door-to-door survey and an interview (phase I). Then, neurologists evaluated suspected cases and randomly selected negative persons to estimate epilepsy prevalence (phase II). In phase III, all participants were offered noncontrast computed tomography (CT) for identifying NCC cases. The independent association between NCC (exposure) and epilepsy (outcome) was assessed by the use of multivariate logistic regression models adjusted for age, sex, level of education, and alcohol intake. CT findings were subsequently compared to archived brain magnetic resonance imaging in a sizable subgroup of participants.

RESULTS

Of 1,604 villagers aged ≥20 years, 1,462 (91%) were enrolled. Forty-one persons with epilepsy (PWE) were identified, for a crude prevalence of epilepsy of 28 per 1,000 population (95% confidence interval [CI] = 20.7-38.2). A head CT was performed in 1,228 (84%) of 1,462 participants, including 39 of 41 PWE. CT showed lesions consistent with calcified parenchymal brain cysticerci in 118 (9.6%) cases (95% CI = 8.1-11.4%). No patient had other forms of NCC. Nine of 39 PWE, as opposed to 109 of 1,189 participants without epilepsy, had NCC (23.1% vs. 9.2%, p = 0.004). This difference persisted in the adjusted logistic regression model (odds ratio = 3.04, 95% CI = 1.35-6.81, p = 0.007).

SIGNIFICANCE

This large CT-based study demonstrates that PWE had three times the odds of having NCC than those without epilepsy, providing robust epidemiological evidence favoring the relationship between NCC and epilepsy.