Unilateral holohemispheric central nervous system lesions associated with medically refractory epilepsy in the pediatric population: a retrospective series of hemimegalencephaly and Rasmussen's encephalitis

Rasmussen Encephalitis: Clinical Features, Pathophysiology, and Management Strategies-A Comprehensive Literature Review

Rasmussen encephalitis (RE) is a rare and progressive form of chronic encephalitis that typically affects one hemisphere of the brain and primarily occurs in pediatric individuals. The current study aims to narratively review the literature about RE, including historical information, pathophysiology, and management of this condition. RE often occurs in individuals with normal development, and it is estimated that only a few new cases are identified each year in epilepsy centers. Approximately 10% of cases also occur in adolescents and adults. The hallmark feature of RE is drug-resistant focal seizures that can manifest as epilepsia partialis continua. Also, patients with RE usually develop motor and cognitive impairment throughout the years. Neuroimaging studies show progressive damage to the affected hemisphere, while histopathological examination reveals T-cell-dominated encephalitis with activated microglial cells and reactive astrogliosis. The current therapy guidelines suggest cerebral hemispherotomy is the most recommended treatment for seizures in RE, although significant neurological dysfunction can occur. Another option is pharmacological management with antiseizure medications and immunomodulatory agents. No significant progress has been made in understanding the pathophysiology of this condition in the last decades, especially regarding genetics. Notably, RE diagnosis still depends on the criteria established by Bien et al., and the accuracy can be limited and include genetically different individuals, leading to unexpected responses to management.

Hemimegalencephaly: A Systematic Comparison of Functional and Anatomic Hemispherectomy for Drug-Resistant Epilepsy

BACKGROUND AND OBJECTIVES

Hemimegalencephaly (HME) is a rare diffuse malformation of cortical development characterized by unihemispheric hypertrophy, drug-resistant epilepsy (DRE), hemiparesis, and developmental delay. Definitive treatment for HME-related DRE is hemispheric surgery through either anatomic (AH) or functional hemispherectomy (FH). This individual patient data meta-analysis assessed seizure outcomes of AH and FH for HME with pharmacoresistant epilepsy, predictors of Engel I, and efficacy of different FH approaches.

METHODS

PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health Literature were searched from inception to Jan 13th, 2023, for primary literature reporting seizure outcomes in >3 patients with HME receiving AH or FH. Demographics, neurophysiology findings, and Engel outcome at the last follow-up were extracted. Postsurgical seizure outcomes were compared through 2-tailed t -test and Fisher exact test. Univariate and multivariate Cox regression analyses were performed to identify independent predictors of Engel I outcome.

RESULTS

Data from 145 patients were extracted from 26 studies, of which 89 underwent FH (22 vertical, 33 lateral), 47 underwent AH, and 9 received an unspecified hemispherectomy with a median last follow-up of 44.0 months (FH cohort) and 45.0 months (AH cohort). Cohorts were similar in preoperative characteristics and at the last follow-up; 77% (n = 66) of the FH cohort and 81% (n = 38) and of the AH cohort were Engel I. On multivariate analysis, only the presence of bilateral ictal electroencephalography abnormalities (hazard ratio = 11.5; P = .002) was significantly associated with faster time-to-seizure recurrence. A number-needed-to-treat analysis to prevent 1 additional case of posthemispherectomy hydrocephalus reveals that FH, compared with AH, was 3. There was no statistical significance for any differences in time-to-seizure recurrence between lateral and vertical FH approaches (hazard ratio = 2.59; P = .101).

CONCLUSION

We show that hemispheric surgery is a highly effective treatment for HME-related DRE. Unilateral ictal electroencephalography changes and using the FH approach as initial surgical management may result in better outcomes due to significantly lower posthemispherectomy hydrocephalus probability. However, larger HME registries are needed to further delineate the predictors of seizure outcomes.

Rasmussen's encephalitis is characterized by relatively lower production of IFN-β and activated cytotoxic T cell upon herpes viruses infection

Background

The etiology of Rasmussen's encephalitis (RE), a rare chronic neurological disorder characterized by CD8+ T cell infiltration and unihemispheric brain atrophy, is still unknown. Various human herpes viruses (HHVs) have been detected in RE brain, but their contribution to RE pathogenesis is unclear.

Methods

HHVs infection and relevant immune response were compared among brain tissues from RE, temporal lobe epilepsy (TLE) and traumatic brain injury (TBI) patients. Viral antigen or genome, CD8+ T cells, microglia and innate immunity molecules were analyzed by immunohistochemical staining, DNA dot blot assay or immunofluorescence double staining. Cytokines were measured by multiplex flow cytometry. Cell apoptosis was visualized by TUNEL staining. Viral infection, immune response and the severity of unihemispheric atrophy were subjected to correlation analysis.

Results

Antigens of various HHVs were prevalent in RE and TLE brains, and the cumulative viral score of HHVs positively correlated with the unihemispheric atrophy in RE patients. CD8+ T cells infiltration were observed in both RE and TLE brains and showed co-localization with HHV antigens, but their activation, as revealed by Granzyme B (GZMB) release and apoptosis, was found only in RE. In comparison to TLE, RE brain tissues contained higher level of inflammatory cytokines, but the interferon-β level, which was negatively correlated with cumulative viral score, was relatively lower. In line with this, the DNA sensor STING and IFI16, rather than other innate immunity signaling molecules, were insufficiently activated in RE.

Conclusions

Compared with TBI, both RE and TLE had prevalently HHV infection and immune response in brain tissues. However, in comparison to TLE, RE showed insufficient activation of antiviral innate immunity but overactivation of cytotoxic T cells. Our results show the relatively lower level of antiviral innate immunity and overactivation of cytotoxic T cells in RE cases upon HHV infection, the overactivated T cells might be a compensate to the innate immunity but the causative evidence is lack in our study and need more investigation in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02379-0.

Hemimegalencephaly and tuberous sclerosis complex: A rare yet challenging association

Hemimegalencephaly is a rare malformation of cortical development characterised by enlargement of one cerebral hemisphere. The association between hemimegalencephaly and tuberous sclerosis complex, an autosomal dominant genetic disorder, is uncommon and has so far been reported only in a few cases. Intractable epilepsy and severe developmental delay are typical clinical manifestations. Aberrant activation of the mTOR signalling pathway is considered to be the hallmark of the pathogenesis of these two disorders. Thus, mTOR inhibitors such as everolimus represent a promising therapeutic approach to mTOR-associated manifestations. We present a thorough literature review of the association between hemimegaloencephaly and tuberous sclerosis complex.

Seizure outcomes in children with Rasmussen's encephalitis undergoing resective or hemispheric epilepsy surgery: an individual participant data meta-analysis

OBJECTIVE

The objective of this study was to perform an individual participant data meta-analysis to identify preoperative factors associated with a good seizure outcome in children with Rasmussen's encephalitis (RE) undergoing resective or hemispheric epilepsy surgery.

METHODS

Electronic databases (PubMed, Web of Science, CINAHL) were searched with no language or date restrictions to identify cohort studies of consecutive participants undergoing resective surgery that reported seizure outcomes. The authors recorded all preoperative factors that could plausibly be associated with seizure outcomes and used Cox regression analysis to identify which of these variables were associated with seizure freedom (i.e., Engel class I).

RESULTS

Of 720 citations, 19 articles reporting on 187 participants were eligible. Seizure freedom (Engel class I) was observed in 113 participants (60.4%). On univariate analyses, younger age at disease onset (hazard ratio [HR] 0.906, p = 0.001), younger age at surgery (HR 0.928, p < 0.001), shorter time to surgery (HR 0.921, p = 0.001), and hemispherectomy (HR 0.283, p < 0.001) were all associated with longer time to postoperative seizure recurrence. Additionally, multivariable analysis including the aforementioned variables showed that younger age at surgery (HR 0.946, p = 0.043) and hemispherectomy (HR 0.297, p < 0.001) were independently and significantly associated with a greater time to seizure recurrence and longer duration of seizure freedom.

CONCLUSIONS

The majority of pediatric patients undergoing resective or hemispheric surgery for RE achieve good seizure outcome. Although small retrospective cohort studies are inherently prone to bias, the best available evidence utilizing individual participant data suggests hemispheric surgery and younger age at surgery are associated with good seizure outcomes following epilepsy surgery. Large, multicenter observational studies with long-term follow-up are required to evaluate the risk factors identified in this review.