IntroductionBrain perfusion deficits have been reported previously in patients with Parkinson's disease (PD) and multiple system atrophy (MSA). However, clinical differential diagnosis between mildly symptomatic PD and the Parkinson's variant of MSA (MSA-P) is difficult because of the similarity of symptoms between parkinsonian disorders. Accurate diagnosis of these disorders is important for treatment decisions, appropriate advice, management, and prognosis. Therefore, we conducted this study to investigate the difference in perfusion single-photon emission computed tomography (SPECT) between patients with mild symptomatology of PD and those with MSA-P using the SPM program.Patients and methodsWe consecutively recruited 47 patients with PD, 21 patients with MSA-P, and 48 age-matched healthy controls. All participants underwent Tc-99m hexamethylpropyleneamine oxime (HMPAO) perfusion SPECT, and the perfusion images were analyzed.ResultsPerfusion SPECT showed hypoperfusion in the frontal cortex in both PD and MSA-P patients compared with healthy controls. Hypoperfusion in the occipital cortex was seen only in PD patients. There are no significant intercorrelations of blood flow in the cerebral region between PD and MSA-P patients.ConclusionWe cautiously assume that the only difference in cerebral blood perfusion images of mild symptomatic PD and MSA-P patients is blood perfusion in the occipital cortex. Although there are many cerebral regions with similar perfusion in patients with PD and MSA-P of mild symptomatology, we could assume that each has a completely different pathophysiology for PD and MSA-P because of the lack of significant intercorrelation of blood flow in the cerebral region.