FDG- and Dopa-PET in postencephalitic parkinsonism

We report a case of a 74-year old woman who following an acute virus encephalitis developed an akinetic-rigid Parkinson syndrome with tremor, hypokinesia, hypomimia, rigidity and cogwheel phenomenon in all four extremities, brady-dysdiadochokinesia as well as myoclonic jerks of the arms. Many of the clinical features of this postencephalitic parkinsonism (PEP) suggested the diagnosis of sporadic encephalitis lethargica, first described by von Economo 1917. Cerebral spinal fluid showed signs of a viral encephalitis, and a positive influenza A IgA-antibody titer (1:>160) in the viral serologic screen was found. Positron emission tomography (PET) showed an altered pattern of glucose- and dopa-metabolism clearly different from findings in idiopathic Parkinson syndrome (IPS). The acute lack of inhibitory input from the substantia nigra pars compacta to the striatum could explain the different metabolic patterns in our case in comparison to IPS patients. Our findings indicate that PEP may also be caused by influenza A and furthermore that PET clearly distinguishes PEP from IPS.