[A follow-up study on brainstem atrophy in progressive supranuclear palsy--when does brain MRI contribute to the differential diagnosis between progressive supranuclear palsy and Parkinson disease?].

OBJECTIVE: To investigate when the MRI can discriminate progressive supranuclear palsy (PSP) from Parkinson disease (PD). METHODS: We obtained the following parameters using T1-weighted axial images of the midbrain and the middle pons from 40 studies of 17 PSP patients and 26 studies of 26 PD patients; 1. anteroposterior diameter of the pons (Pons AP), 2. anteroposterior length of the pontine tegmentum (Pons T), 3. anteroposterior diameter of the midbrain (Midbrain AP), 4. ratio of anteroposterior diameter of the pontine base to that of the pontine tegmentum (Pons B/T ratio), 5. ratio of the sum of the bilateral crus cerebri widths to the midbrain AP (Midbrain [Cr + Cl]/AP ratio). All the PSP patients were studied more than twice and each study was classified into four groups according to the duration of the illness; (1) less than 24 months (7 studies), (2) from 24 to 47 months (10 studies), (3) from 48 to 71 months (14 studies) and (4) 72 months or longer (9 studies). RESULT: The first MRI studies (duration of disease 39.9 +/- 22.1 months) were compared with the second studies (duration of disease 67.6 +/- 31.6 months) in 17 PSP patients. Pons AP, Pons T, and Midbrain AP were significantly smaller in the second studies, indicating progressive pontine and midbrain atrophy. Compared with the PD group, the PSP group showed significant atrophy four years after onset of the disease in Pons AP and two years in Pons T. Pons B/T ratio, and Midbrain [Cr + Cl]/AP ratio were significantly smaller in the PSP group two years after onset, suggesting midbrain and pontine tegmentum atrophy. The diagnostic MRI criteria of Pons B/T ratio more than four and Midbrain [Cr + Cl]/AP ratio more than two each showed accuracy in PSP of more than 70% two years after onset. CONCLUSIONS: Discrimination of PSP from PD was difficult during the first two years after onset. The atrophic process in the midbrain and the pontine tegmentum may precede that of the pontine base. Pons B/T ratio and Midbrain [Cr + Cl]/AP ratio presented here are potentially good indexes for the discrimination of these two diseases.