Autoimmune encephalitis (AE) associated with antibodies to NMDA-receptors of neurons is a relatively recently established acute and severe form of encephalitis the development of which is associated with the production of antibodies to NR1 and NR2 heteromers of NMDA-receptors [1,2]. In children, this clinical phenotype of anti-NMDA-receptor encephalitis was previously treated as dyskinetic lethargic encephalitis or immune choreic lethargy syndrome [3]. In the California Encephalitis Project [4], the incidence of antiNMDA-receptor encephalitis was superior to that of any viral encephalitis [5,6], and 40 % of patients were younger than 18 years [2]. In children, a concomitant neoplastic process is rare. Although approximately 56 % of women over age 18 have unilateral or bilateral teratomas of the ovary, these tumours also occur in 30 % of girls under age 18 and 9 % of girls under age 14 [7,8].

Pathogenetically, anti-NMDAR autoimmune encephalitis involves the dopaminergic system in the pathological process (rigidity, dystonia, orofacial movements, tremor), autonomic dysfunction occurs (cardiac arrhythmias, hypertension, hypersalivation), and the development of central hypoventilation is natural. This is explained by the fact that the main targets of the autoimmune response — NR1 and NR2 heteromers of receptors are expressed mainly in the forebrain, including the prefrontal cortex, hippocampus, amygdala and hypothalamus. Hyperkinesias are nonepileptic, so they are resistant to antiepileptic drugs (AEDs) and sedatives and are not accompanied by changes in EEG monitoring [3].

The disease begins similarly in adults and adolescents and usually develops in stages, including a prodromal phase of fever, headache or virus-like symptoms that often go unnoticed. The appearance of obvious clinical signs is associated with the appearance of psychopathological disorders, including anxiety, restlessness, fears, sleep disorders, strange pretentious behaviour, delusions (often religious content), hallucinations, memory disorders (loss of short-term memory) and speech disorders (rapid decay up to mutism), so it is extremely difficult to suspect the disease [9]. Such patients are first hospitalized or treated by psychiatrists, often with a diagnosis of endogenous disease, whereas only early immunomodulatory treatment can completely cure the patient and return to normal life [10]. According to the available literature, in recent years cases of AE have been identified in psychiatric inpatients with initial diagnoses of schizophrenia, schizoaffective disorder, narcolepsy and major depressive disorder [11]. The main differential diagnosis of the disease is carried out with viral encephalitis, neuroleptic malignant syndrome, acute psychosis and drug abuse [9]. In children, classical symptoms of psychosis observed in adults are less common, but regression of behaviour and observable speech disorders are often noted [1,4,12]. Symptoms progress rapidly, and as encephalitis progresses, there is a worsening of the severity of the disease, it manifests by impaired consciousness and convulsive seizures. At the stage of clear manifestations, catatonic manifestations and dyskinesias are characteristic. Motor disorders are varied — along with dystonic postures, rigidity and opisthotonus may be noted. Orolingual-facial dyskinesias, oculogyric crises and choreoathetosis are common. Autonomic disorders — hyperthermia, heart rhythm disorders, tachycardia or bradycardia, hypersalivation, AT fluctuations, urinary incontinence, hypoventilation — are expressed [2,13]. In the stage of advanced clinical manifestations, patients need intensive care in an intensive care unit [14].