Autoimmune encephalitis: possibilities in the laboratory investigation]

Introduction: The role of autoimmune responses against central nervous system (CNS) antigens in encephalitis presenting with non-classified neurologic or psychiatric symptoms has been appreciated in the past decade. Paraneoplastic limbic encephalitis has a poor prognosis and is most commonly associated with lung, ovarium, and testicular neoplasms, leading to immune reactions against intracellular antigens (anti-Hu/ANNA1, anti-Ri/ANNA2, anti-CV2/CRMP5 and anti-Ma2/Ta). In contrast, the recently described autoimmune encephalitis subtypes present with a broad spectrum of symptoms, respond to autoimmune therapies well and usually associate with autoantibodies against neuronal cell surface receptors (NMDAR, GABABR, AMPAR) or synaptic proteins (LGI1, CASPR2). Aim: Our aim is to bring to awareness the increasing number of autoimmune encephalitis patients requiring neurologic, psychiatric and intensive care and to emphasize the significance of detecting various autoantibodies in diagnosing patients. Method: In the past 6 years, our laboratory received 836 autoimmune encephalitis diagnostic test requests from a total of 717 patients. Serum and cerebrospinal fluid (CSF) samples were analysed with indirect immunofluorescence using a BIOCHIP consisting of cell lines transfected with 6 different receptor proteins. Results: IgG autoantibodies against receptor proteins were present in 7.5% of patients. The frequency of positive samples was the following: NMDAR > LGI1 > GABABR > CASPR2. Conclusion: Detecting autoantibodies facilitates the diagnosis of autoimmune encephalitis in an early stage. Patients diagnosed early can be effectively treated with plasmapheresis and immunosuppressive drugs. The efficiency of therapies can be monitored by autoantibody detection. Therefore, the diagnostic immune laboratory plays an important role in proper diagnosis and in the prevention of rapidly progressing symptoms.