To delineate the characteristics of PUT-hypo of MSA-P.

Hypo-intensity in the posterolateral putamen (PUT-hypo) on iron-sensitive MR sequences has been recognized as a biomarker of MSA-P, which reflects the pathological iron deposition. On the other hand, several previous reports have noted that the same pattern of iron deposition in the putamen can be caused by aging.

Five patients with MSA-P and 7 with PD who were diagnosed clinically were enrolled. Five stroke patients without parkinsonism were also included as age-matched controls. To observe PUT-hypo on SWI by 1.5-T MR, I focused on the phase image (SWI-phase). SWI-phase is more sensitive to iron deposition than SWI magnitude images. The region-of-interest (ROI) method was used to measure the mean signal value of the region to process the PUT-hypo image. To evaluate the characteristics of PUT-hypo, two kinds of images were processed: (1) PUT-hypo(PUT) processed using the mean signal value of the entire putamen as the upper threshold to omit the region with a higher signal value, and (2) PUT-hypo(GP) processed using the mean signal value of entire globus pallidus as the upper threshold to omit the region with a higher signal value.

Both types of PUT-hypo images were observed in all groups. The signal values of PUT-hypo were lower in MSA-P than in the other groups. The degree of decrease was most significant in PUT-hypo(PUT); signal values were -368 in MSA-P, -235 in PD, and -205 in age-matched controls. There was no difference in area among them.

PUT-hypo is a non-specific finding that can be observed in the elderly. The degree of decrease in the signal value may be more important for differentiation of MSA-P than the area of distribution. PUT-hypo should be evaluated in greater detail.