According to the Chinese expert consensus on the diagnosis and management of autoimmune encephalitis, the criteria for definite diagnosis of LGI1-antibody encephalitis are as follows: (1) having acute or subacute onset with progressive aggravation; (2) presenting with clinical features of limbic encephalitis or FBDS; (3) having normal leukocyte count or mild lymphocyte reaction on CSF examination; (4) showing abnormal brain MRI signals in the bilateral or unilateral medial temporal lobe; (5) showing abnormal EEG activity; and (6) tested positive for serum and/or CSF anti-LGIl antibody. The case presented here had an acute onset of the disease and experienced frequent panic attacks, which is a clinical feature of limbic encephalitis. These symptoms, combined with the abnormal EEG findings and positive anti-LGIl antibody in the serum and CSF, supported the diagnosis of LGI1-antibody encephalitis.
The LGI1-antibody encephalitis occurs predominantly in males, with a mean onset age of ~ 60 years (typical range, 30–80 years) . Pediatric cases have been rarely reported . Schimmel reported in 2017 a 14-year-old boy who was diagnosed with the LGI1-antibody encephalitis , and Zhang et al. reported an 8-year-old Chinese boy with the symptom of reduced night-time sleep in 2018 . Therefore, to our best knowledge, the patient reported here is the youngest case reported to date.
Autoimmune encephalitis is a type of inflammation in the central nervous system. Studies have reported that the LGI1-antibody encephalitis is the second most common form of autoimmune encephalitis . There is a high incidence of epileptic seizures during the acute phase of autoimmune encephalitis. In this context, the seizures may be an acute or induced symptom, and can be considered as autoimmune seizures, which has a prevalence of 60–100% . According to the 2014 edition of Epilepsy Usability Definition by the International League Against Epilepsy (ILAE) , the acutely provoked or acute symptomatic seizures at this stage cannot yet be defined as epilepsy. In 2017, the ILAE further proposed a new classification of epilepsy, the “epilepsy of immune etiology”, for patients whose epilepsy “results directly from an immune disorder in which seizures are a core symptom of the disorder” . Multiple frequent seizure semiology and subclinical seizures associated with temporal and frontal discharges have been reported in the LGI1-antibody encephalitis patients , and in our case the discharges were also concentrated in the frontal lobe. Some cases also showed frequent early seizures of encephalitis as clinical manifestations . Consistently, the case in our report also displayed seizures as the first symptom.
In addition, the symptoms, the presence of antibody, and the treatment response of this case were all similar to those of adult patients. However, our patient did not show FBDS or hyponatremia, which are hallmark symptoms in adult patients with LGI1-antibody encephalitis . Therefore, the diagnosis of LGI1-antibody encephalitis should be considered if pediatric patients display acute and progressing unexplained frequent episodes of seizures, in order to prevent misdiagnosis and missed diagnosis. In fact, seizures are extraordinarily frequent in the acute, inflammatory-provoked phase of many types of antibody-mediated encephalitis, especially in the LGI1-antibody encephalitis, but in most patients the seizures are not sustained and will resolve after the encephalitis remission . However, a recent study showed that after 2 years’ follow-up, 14% of patients with LGI1-antibody encephalitis still had seizures and an additional 14% were still on AEDs after the encephalitis was cured . Some scholars have suggested that the epileptiform seizures in the acute phase of autoimmune encephalitis cannot be diagnosed as epilepsy, instead, it should be followed up for at least 1 year to detect the presence of persistent seizures to determine the continued use of AEDs . It is currently believed that the abnormalities in EEG and brain imaging are the most predictive factors for epilepsy after autoimmune encephalitis . In this report, the patient showed normal results of brain imaging, and her seizures and EEG abnormality were improved as her encephalitis was controlled. However, as the follow-up time was not long enough in this report, we would continue to follow up to observe the prognosis of this patient.