Fever to Tremor: Exploring the link between Encephalitis and Parkinsonian Syndrome

The inflammation of the brain's parenchyma is known as encephalitis.  The main culprits are arboviruses, varicella-zoster virus, and herpes simplex virus.  Despite being a chronic consequence of encephalitis, post-encephalitic parkinsonism (PEP) often manifests as a febrile illness with neurological dysfunction. Since then, PEP, a secondary parkinsonian syndrome, has been linked to autoimmune, bacterial, and viral origins. This study examines the etiological, clinical, and neuropathological differences between PEP and idiopathic Parkinson's disease (PD). PEP differs from Parkinson's disease in that it is defined by extensive tau pathology rather than α-synuclein aggregates (Lewy bodies), lacks considerable iron buildup, and often affects younger individuals with unusual symptoms such as ocular palsy and oculogyric crises. Instead of direct viral damage, pathogenesis is assumed to be caused by autoimmune processes such as molecular mimicry and bystander activation. Due to its latency period between encephalitis and the onset of symptoms, as well as its overlapping symptoms with Parkinson's disease, PEP is currently difficult to diagnose. Neuroimaging frequently shows basal ganglia and brainstem hyperintensities to differentiate PEP from PD.  The mainstay of treatment regimens is levodopa and other dopaminergic drugs; however, due to the increased risk of neuropsychiatric adverse effects, such as emotional dysregulation and impulse control issues, their effectiveness has varied. The study highlights the need for longitudinal studies to address the lack of knowledge on tau pathology, autoimmune mechanisms, and viral factors in PEP. New methods of diagnosis and treatment are needed to improve outcomes in this uncommon condition. The objective of this research is to increase our understanding of post-encephalitic parkinsonism to develop better management strategies for the condition, given its similarities to idiopathic Parkinson's disease and other developments in neuroimaging and immunology.