Basically, Encephalitis is inflammation of the brain, caused either by an infection invading the brain (infectious); or through the immune system attacking the brain in error (post-infectious or autoimmune Encephalitis). Over the past decade, it has become increasingly recognized that autoimmune conditions contribute significantly to the spectrum of encephalitis causes. Certain forms of encephalitis have specific treatments; hence, establishing a diagnosis rapidly and accurately is crucial. Furthermore, a diagnostic algorithm to detect and characterize neuronal cell surface autoantibodies is suggested and some of the caveats of serum testing are outlined. There have been a couple of recent reports over the past year as well as a new condition; I hope you’ll spend a couple of minutes to hear about it and perhaps click on some of the references cited below. Blood samples from these subjects were screened for six neuronal antibodies. It is easier to understand this category of illnesses in terms of neuroanatomical involvement.
While the former are believed to be pathogenic since they can access their targets on the membrane of live cells, the latter are likely to be markers of immune-mediated disease but unlikely to themselves be pathogenic. The discovery of autoantibodies specific for the neuronal cell membrane surface or synaptic proteins has led to the emergence of the novel concepts of autoimmune epilepsy and autoimmune encephalitis. The composite CBAs contained chips expressing the following antigens: (1) NMDA-R, AMPA-R, and GABAB-R; (2) LGI-1 and CASPR2; (3) mGluR1, mGluR5, and DPPX. In individual patients, the reduction of antibody levels is accompanied by clinical improvement. Magnetic resonance imaging (MRI) scans revealed mesial temporal abnormalities in nine patients. Computed tomography (CT) and magnetic resonance imaging (MRI) showed no brain abnormalities. The identification of specific antigens was important in generating animal models which developed experimental autoimmune MG after they received the antibody or were immunized with the target antigen.
Many of these principles are also true for the Lambert-Eaton myasthenic syndrome. This illustration of antibody-mediated disease in the peripheral nervous system2,5,6 illuminates some of the ways by which Abs can cause disease at a simple synapse and might offer some insight as to the potential complexity associated with studying their actions on central neuronal networks. Exactly why the immune system malfunctions in this way is unclear. Viral encephalitis and metabolic conditions, such as herpes simplex encephalitis and Wernicke’s encephalopathy, respectively, can present with similar features. The clinical features can help make the diagnosis of an autoimmune process and then guide the rational identification of an associated Ab (see Table 1). Therefore, autoimmune encephalitides may be subdivided according to the antigen recognized by patient Abs. As reviewed by Vincent and colleagues, the most common and well researched associated Abs are directed against the voltage-gated potassium channel-complex (VGKC-complex), N-methyl D-aspartate receptor (NMDAR) and glutamic acid decarboxylase (GAD).4 Small case series have also described patients with Abs against glycine receptors, amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), and gamma-aminobutyric B receptors (GABABR).