Autoimmune encephalitis

Autoimmune encephalitis
Classification and external resources
ICD-10	G04.81
ICD-9-CM	323.81
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Autoimmune encephalitis (or autoimmune encephalopathy) is a diverse group of neuro-psychiatric disorders recognized recently, presenting acutely or subacutely with alteration of consciousness, cognitive decline, seizure, abnormal movements. Associated with systemic autoimmune disorders, CNS autoimmune disorders and paraneoplastic syndromes. Pathogenesis is likely to be mediated by antibodies (Abs) to CNS proteins. The Abs are directed against membrane receptors and ion channel-associated proteins that are expressed on the surface of neurons in the CNS, such as N-methyl D-aspartate receptors and leucine-rich, glioma inactivated protein and contactin-associated protein like, that are associated with voltage-gated potassium channels. The diseases are not invariably cancer-related and are therefore different from the classical paraneoplastic neurological diseases that are associated with, but not caused by, Abs to intracellular proteins. Diagnosis of autoimmune encephalopathy is based on the clinical course, serologic evidence of autoimmunity, severe but nonspecific slowing on electroencephalography, and evidence of intrathecal inflammation in the cerebrospinal fluid and neuroimaging by MRI. Treatment include first-line steroids, intravenous immunoglobulins(IVIG), and plasma exchange, and second-line Rituximab and Cyclophosphamide, followed in many cases by steroid-sparing agents in the long-term.

Sydenham's chorea epidemic was first documented in 1418 and later in 1686 Thomas Sydenham described the condition. The association of chorea with rheumatism was first recognized in 1802 and several cases has been reported by French and English workers during nineteenth century. It was Richard Bright who in 1831 who first made the association between chorea and rheumatic fever. The evidence suggesting that it may be mediated by streptococcal antibodies that cross-react with the brain was published in 1993.

In 1916, von Economo described encephalitis lethargica (EL), a CNS disorder presenting with pharyngitis followed by sleep disorder, basal ganglia signs (particularly parkinsonism) and neuropsychiatric sequelae. Since the 1916–1927 epidemic, only sporadic cases have been described. Pathological studies revealed an encephalitis of the midbrain and basal ganglia, with lymphocyte (predominantly plasma cell) infiltration. The EL epidemic occurred during the same time period as the 1918 influenza pandemic, and the two outbreaks have been linked in the medical literature. However, von Economo and other contemporary scientists thought that the 1918 influenza virus was not the cause of EL. Recent examination of archived EL brain material has failed to demonstrate influenza RNA, adding to the evidence that EL was not an invasive influenza encephalitis. By contrast, the findings of intrathecal oligoclonal bands (OCB) and beneficial effects of steroid treatments have provoked the hypothesis that EL may be immune‐mediated.

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