Isolated involvement of substantia nigra in acute transient parkinsonism: MRI and PET observations

A woman, aged 27 years, developed acute headache and fever followed by tremor, rigidity, and bradykinesia. Masked face, drooling saliva, monotonous voice, and dysphagia were observed. She was totally bedridden during the worst period because of marked generalized rigidity and bradykinesia. There was no neurological disturbance other than parkinsonism. Several herpetic vesicles were noticed at the left angle of her mouth. The cerebrospinal fluid revealed a mononuclear pleocytosis with a normal concentration of sugar and protein. The antibody test for Type I herpes simplex virus was positive in the serum but negative in the cerebrospinal fluid. Brain CT and EEG were normal. However, MRI study showed markedly increased signals in the bilateral substantia nigra on T2-weighted, proton density, and in gradient recall acquisition imagings. Those abnormal findings had almost disappeared in a follow-up MRI study 2 months later. Her parkinsonian symptoms were substantially resolved by the time. However, PET scans, performed 8 months later, disclosed: (1) mild reduction of fluorodopa uptake; and (2) increased raclopride binding, predominantly in the putamen. These findings suggest a subclinical nigrostriatal dopaminergic deficit and a relative excess of the D2 receptors, with a pattern similar to that found in typical idiopathic parkinsonism.