Improvement in mild anti-IgLON5 encephalopathy without immunotherapy: a case report

BACKGROUND: Anti-IgLON5 antibody-related encephalopathy is a recently discovered and rare autoimmune disease, and its diagnosis and treatment are more challenging than for other autoimmune encephalopathic diseases. Sleep disorder is the most prominent symptom of the disease. It can also present with gait instability, dysarthria, dysphagia, dementia, ataxia, autonomic nervous system dysfunction, chorea, vertical gaze paralysis, and other symptoms. Immunotherapy remains the primary treatment for this disease; however, there is no definitive conclusion regarding the effect of immunotherapy. The clinical symptoms of the reported cases of anti-IgLON5 antibody-related encephalopathy were generally severe. However, the symptoms in our patient were mild and relieved without immunotherapy, unlike the previously reported cases. CASE PRESENTATION: A 62-year-old man presented with behavioural abnormalities and involuntary movements after nearly 2 months of fever and headache. He also had symptoms of mild sleep disorder. Due to the abnormal levels of infection-related indicators, antiviral treatment was started on the day of admission. The serum analysis confirmed the presence of IgLON5 antibody, and the patient was found to be genetically susceptible. The patient's symptoms resolved rapidly without immunotherapy and did not recur. CONCLUSIONS: This case demonstrated that IgLON5 antibody-related encephalopathy might have mild manifestations. Infection and a genetic predisposition may be important causes for the disease. Patients with a mild disease may have a better prognosis.