SECONDARY PARKINSONISM DUE TO FOCAL SUBSTANTIA-NIGRA LESIONS - A PET STUDY WITH [F-18] FDG AND [F-18] FLUORODOPA

We present a 71 year old woman with predominantly right sided parkinso nism of sudden onset, but without tremor. Magnetic resonance imaging ( MRI) depicted lesions affecting the substantia nigra (SN) bilaterally, but more pronounced on the left side. There were no other discernible structural lesions. Using positron emission tomography (PET), we inve stigated regional cerebral metabolic rate of glucose (rCMRG) using the tracer [F-18]-fluorodeoxyglucose (FDG), and striatal dopa decarboxyla se capacity using the tracer [F-18]-L-6-fluorodopa (FDOPA). The degree and pattern of distribution of FDOPA uptake reductions (putamen > cau date nuclei) were similar to those in idiopathic Parkinson's disease ( PD). FDG uptake also revealed similar changes (reductions in frontal c ortex and cerebellum, but increases in thalamus), except for putamen w hich showed reduced rCMRG. In conclusion, the absence of tremor at res t accords with experimental SN lesions. The PET findings in this atypi cal condition are explained in terms of deafferentation of various bra in regions involved in motor control. Furthermore, they illustrate the metabolic effects related to acute focal lesions of the SN as opposed to the progressive degeneration in idiopathic PD and may serve to hel p unravel the complicated pathophysiology underlying these conditions.