Parkinsonism Due to Predominant Involvement of Substantia Nigra in Japanese Encephalitis
abstract & commentary
Source: Pradhan S, et al. Parkinsonism due to predominant involvement of substantia nigra in Japanese encephalitis. Neurology 1999;53:1781-1786.
In this paper, pradhan and colleagues report their finding of a new clinicopathologic pattern for Japanese encephalitis (JE). JE is the most common endemic encephalitis seen in Southeast Asia and India. The virus usually affects the thalamus, brainstem, anterior horn cells, and cerebral cortex, but may also affect the basal ganglia and cerebellum. While prior reports had shown occasional involvement of the substantia nigra, Pradhan et al recognized a new pathologic pattern that selectively involved the nigra, sparing all other brain regions.
Of the 52 patients they encountered with JE over a period of six years, five patients shared a strikingly similar clinical and radiologic phenotype. All of these patients were young (ages 7-16), and all presented with a prodrome of encephalitis (fever, headache, altered level of arousal, and seizures). On examination during their acute illness, upbeating nystagmus and opsoclonus were accompanied by severe parkinsonism, with prominent cogwheeling, tremor, and rigidity. Cerebrospinal fluid analysis revealed a mild leukocytosis with mild elevation in protein and normal glucose. The diagnosis of JE was secured by demonstrating at least a four-fold rise in serum antibody titers to the virus. Despite the severe nature of their illness, three of five patients recovered completely at one-year follow-up, and two other patients were recovering when seen two months after their acute illness.
The most striking feature of these patients was the appearance of their magnetic resonance imaging (MRI) scans. In all five patients, the substantia nigra appeared hyperintense on T2-weighted images and hypointense on T1 views. There was no enhancement with contrast, and no lesions were seen in any other areas of the brain.
Commentary
There has long been heated debate whether Parkinson’s disease (PD) is predominantly genetic or if it is related to environmental exposure to toxins or viral agents. Viral agents are unlikely to be responsible for the vast majority of PD or parkinsonism. Nevertheless, the discovery of a viral agent with selective propensity for the substantia nigra could have profound implications for understanding the selective vulnerability of this target cell population.
The 1918 epidemic of postencephalitic parkinsonism demonstrated that environmental agents may cause parkinsonism. Although the virus responsible for this epidemic has never been identified, other viruses have been reported to have selective affinity for the substantia nigra, including human immunodeficiency virus (HIV) and coxsackie viruses. With this report, Pradhan et al have added JE to this list. Although neurologists in the United States are unlikely to encounter patients with JE, these patients are relevant even in a major city. This was demonstrated last summer with the outbreak of a rare but devastating viral encephalitis that produced movement disorders in some of its victims. —steven frucht, md
Viral agents are unlikely to be responsible for the majority of Parkinson’s disease.
a. True
b. False
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