Methods  

Eleven patients with PS and 8 with ET were examined by clinical assessment and¹²³I-FP-CIT SPECT imaging. The modified Hoehn and Yahr Staging Scale and Unified Parkinson’s Disease Rating Scale (UPDRS) were used to assess the stage and severity of the disease. The co-registered MR and SPECT images were created with fusion software included in Neurostat. On the cross section, which shows the largest area of striate, irregular shaped regions of interest corresponding to the striate and occipital cortex were drawn. Then the ratio of specific striatal uptake to non-specific occipital cortex, V3″(F), was calculated. Another calculation was done by VOIClassic, which is a software included in Neurostat to estimate the counts per voxel of anatomically defined regions such as caudate nucleus, putamen, occipital cortex, and total cortex. Using these count data, the ratio of specific striatal uptake to non-specific occipital cortex, V3″(OC), and total cortex, V3″(TC), was calculated.

Results  

A fair linear correlation was observed between V3″(OC) and V3″(F) (y = 1.53x + 1.40; r = 0.756; p < 0.01), as well as between V3″(TC) and V3″(F) (y = 1.24x + 1.43; r = 0.713; p < 0.01). Both V3″(OC) and V3″(TC) yielded similar tendencies. Concerning discrimination between ET and PS, there was a significant difference between the mean V3″ of PS and ET (p < 0.01). Concerning the correlation between V3″ value and the severity of PS, the UPDRS motor score significantly correlated with the V3″(F) value (r_s= -0.816). However, V3″(OC) and V3″(TC) correlated less with UPDRS (r_s = -0.667 and -0.645, respectively).

Conclusions  

Semiquantitative parameters, V3″(OC) and V3″(TC), calculated by VOIClassic including the Neurostat system are useful and easily calculable parameters as well as V3″(F) for the differential diagnosis of PS from ET.