Anti-N-Methyl-D-Aspartate Receptor Encephalitis and Rasmussen-like Syndrome: An Association?

Understanding Childhood Neuroimmune Diseases of the Central Nervous System

Immune-mediated diseases of the central nervous system (CNS) in childhood are a heterogeneous group of rare conditions sharing the inflammatory involvement of the CNS. This review highlights the growing knowledge of childhood neuroimmune diseases that primarily affect the CNS, outlining the clinical and diagnostic features, the pathobiological mechanisms and genetics, current treatment options, and emerging challenges. The clinical spectrum of these conditions is increasingly expanded, and the underlying mechanisms of dysregulation of the immune system could vary widely. Cell-mediated and antibody-mediated disorders, infection-triggered and paraneoplastic conditions, and genetically defined mechanisms can occur in previously healthy children and can contribute to different stages of the disease. The careful evaluation of the clinical presentation and temporal course of symptoms, the specific neuroimaging and immunological findings, and the exclusion of alternative causes are mandatory in clinical practice for the syndromic diagnosis. A common feature of these conditions is that immunotherapeutic agents could modulate the clinical course and outcomes of the disease. Furthermore, specific symptomatic treatments and comprehensive multidisciplinary care are needed in the overall management. We focus on recent advances on immune-mediated demyelinating CNS disorders, autoimmune encephalitis, interferonopathies, and possible neuroimmune disorders as Rasmussen encephalitis. Better knowledge of these conditions could allow prompt diagnosis and targeted immunotherapy, to decrease morbidity and mortality as well as to improve clinical outcomes, reducing the burden of the disease due to possible long-term neuropsychiatric sequelae. Persisting controversies remain in the rigorous characterization of each specific clinical entity because of the relative rarity in children; moreover, in a large proportion of suspected neuroimmune diseases, the immune "signature" remains unidentified; treatment guidelines are mostly based on retrospective cohort studies and expert opinions; then advances in specific molecular therapies are required. In the future, a better characterization of specific immunological biomarkers may provide a useful understanding of the underlying pathobiological mechanisms of these conditions in order to individualize more tailored therapeutic options and paradigms. Multicenter collaborative research on homogeneous groups of patients who may undergo immunological studies and therapeutic trials could improve the characterization of the underlying mechanisms, the specific phenotypes, and tailored management.

Efficacy of perampanel for anti-N-methyl-D-aspartate receptor encephalitis: A case report

RATIONALE

We report this 1st case because perampanel may be effective against the seizures and abnormal behavior that occur in anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis.

PATIENT CONCERNS

The patient was a healthy 26-year-old woman who suddenly developed seizures and exhibited abnormal behavior.

DIAGNOSES

NMDAR encephalitis was diagnosed based on positive NMDAR antibody on cerebrospinal fluid analysis.

INTERVENTIONS

Treatment with anticonvulsants and sedatives was started immediately, along with steroid pulse therapy and plasmapheresis, but these measures did not adequately control the repeated seizures and abnormal behavior. However, with the addition of oral perampanel, an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, the seizures and abnormal behavior promptly disappeared.

OUTCOMES

The patient was transferred to the rehabilitation hospital and returned to her job.

LESSONS

It appears that perampanel rapidly eliminated these clinical features by inhibiting inflow of abnormal glutamic acid and attenuating nerve hyperexcitability by acting as a selective and noncompetitive antagonist of AMPA receptors that had increased in the postsynaptic membrane due to anti-NMDAR encephalitis. To the best of our knowledge, there are no other reports showing that perampanel was effective against anti-NMDAR encephalitis. This case suggests that perampanel may be effective against the seizures and abnormal behavior that occur in anti-NMDAR encephalitis.

Anti-NMDA Receptor Encephalitis: Clinical Features and Basic Mechanisms

In slightly more than 10 years, anti-NMDA receptor (NMDAR) encephalitis has changed from a rare paraneoplastic syndrome to the most common cause of nonviral encephalitis. It presents fulminantly with progressive psychosis, seizures, and autonomic dysfunction, leading to death if untreated. However, rapid recognition and treatment can lead to survival and a return to baseline levels of functioning in many patients. While initially associated with ovarian teratomas, it is now associated with other tumors and can reflect a postviral event. The antibodies to the NMDAR made in this syndrome are pathogenic and are directed at the extracellular domain of the GluN1 subunit. Such antibodies lead to internalization of NMDARs in model systems, leading to a physiological state characterized by NMDAR hypofunction. Analogous disorders, characterized by antibodies to other synaptic receptors, present with neurological and psychiatric dysfunction and also appear to reflect antibody-induced internalization of receptors. However, this simple pathophysiology may be too simplistic to reflect the complexity of events in anti-NMDAR encephalitis. Future scientific investigations may allow a more complete understanding of this disorder and improve treatment of anti-NMDAR encephalitis.