Encephalitis lethargica syndrome: 20 new cases and evidence of basal ganglia autoimmunity.

In 1916, von Economo first 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. We have recently seen 20 patients with a similar EL phenotype, 55% of whom had a preceding pharyngitis. The patients had remarkable similarity to the historical descriptions of EL: sleep disorder (somnolence, sleep inversion or insomnia), lethargy, parkinsonism, dyskinesias and neuropsychiatric symptoms. CSF examination commonly showed elevated protein and OCB (75 and 69% respectively). Investigation found no evidence of viral encephalitis or other recognized causes of rapid-onset parkinsonism. MRI of the brain was normal in 60% but showed inflammatory changes localized to the deep grey matter in 40% of patients. We investigated the possibility that this phenotype could be a postinfectious autoimmune CNS disorder, and therefore similar to Sydenham's chorea. Anti-streptolysin-O titres were elevated in 65% of patients. Furthermore, western immunoblotting showed that 95% of EL patients had autoantibodies reactive against human basal ganglia antigens. These antibodies were also present in the CSF in four patients tested. By contrast, antibodies reactive against the basal ganglia were found in only 2-4% of child and adult controls (n = 173, P < 0.0001). Rather than showing polyspecific binding, these antibodies bound to common neural autoantigens of molecular weight 40, 45, 60 and 98 kDa. Regional tissue comparisons showed that the majority of these autoantigens were specific to or enriched in CNS tissue. Immunohistochemistry with secondary staining localized antibody binding to neurons rather than glial populations. Further investigation is required to determine whether these antibodies affect neuronal function (i.e. whether they are pathogenic anti-neuronal antibodies). Histopathology in one case demonstrated striatal encephalitis with perivenous B- and T-lymphocytic infiltration. We believe an EL-like syndrome is still prevalent, and propose that this syndrome may be secondary to autoimmunity against deep grey matter neurons.

Astrogliosis in von Economo's and postencephalitic Parkinson's diseases supports probable viral etiology.

A marked generalized astrogliosis was observed in the frontal and temporal white matter from a case of von Economo's disease and another of postencephalitic Parkinson's disease, which areas were otherwise devoid of any other demonstrable microscopic lesions. No similar astrocytic reaction of any severity was observed in the same areas in a number of other brain diseases or controls, except when other kinds of lesions were present in the same section, with reactive astrocytes being present within the primary or defining lesion or immediately close by. The marked astrogliosis in von Economo's and postencephalitic Parkinson's diseases in areas "distant" from the primary lesions seeming to indicate extensive pathological involvement, added to the strong qualitative and quantitative similarity of this reaction to that observed in concurrently studied cases of encephalitides caused by the human immunodeficiency virus, lend further factual support to the hypothesis of a viral etiology, albeit unspecified, in both von Economo's and postencephalitic Parkinson's diseases.

Similarities of guamanian ALS/PD to post-encephalitic parkinsonism/ALS: possible viral cause.

Guamanian amyotrophic lateral sclerosis with parkinsonism-dementia (ALS/PD) has been the subject of intensive study since its discovery in 1947 because of its extraordinarily high incidence in a small ethnic group (Chamorros) whose dietary lack and customs have suggested possible causes. As yet, these and other suspected causes have eluded proof. Because of marked similarities between Guamanian ALS/PD and late onset post-encephalitic (encephalitis lethargica) parkinsonism and ALS it is suggested that they have a common cause. The parkinsonism and ALS in the two disorders are clinically very similar and neuropathological studies have shown a very similar distribution of neurofibrillary tangles in neurons. Some clinical differences, such as ocular features in the post-encephalitic cases and dementia in Guamanian ALS/PD, can be explained by differences in the severity of infection and the interval between the encephalitis and onset of sequelae. Although unproven, influenza A (HswilN1 strain) has long been suspected as the cause of encephalitis lethargica because of simultaneous pandemics of the two diseases in the 1920s. Because influenza A can persistently infect cells and has a marked propensity to mutate it is an optimal candidate among other RNA viruses for delayed nervous system infection as a possible cause of ALS/PD.