¹²³I-FP-CIT SPECT diagnostic ability in progressive supranuclear palsy: using core clinical features and MRI for comparison

Objectives: Progressive Supranuclear Palsy (PSP) is listed as core clinical features in the Movement Disorder Society (MDS) 2017 criteria, with ocular motor dysfunction, postural instability, akinesia and cognitive dysfunction. Imaging evidence show predominant midbrain atrophy or hypometabolism, and postsynaptic striatal dopaminergic degeneration as two supportive features. Midbrain atrophy is called "humming-bird sign" or "penguin sign" in the MRI assessment, and there are reports that about 67% of pathologically proven PSP patients are confirmed by these findings. On the other hand, postsynaptic striatal dopaminergic degeneration is proved in ¹²³I-FP-CIT SPECT or PET evaluations, but this condition is considered to be not a specific finding to PSP and is said to be a difficult image to obtain in the initial stage of PSP. In this study, the diagnostic capability of ¹²³I-FP-CIT SPECT was investigated by comparing core clinical features and MRI in the diagnosis of PSP. As far as we could determine, this is the first study that compares these three indicators in the diagnosis of PSP. Materials and Methods: We included 53 patients with clinically suspected PSP who had undergone ¹²³I-FP-CIT SPECTand MRI examinations. The final diagnosis consisted of probable PSP in 20 patients (10 males, 10 females; mean age ± SD, 71.1 ± 6.4 years, 56 - 81 years), and without PSP in 33 patients (20 males, 13 females; mean age, 75.1 ± 11.1 years; range, 46 - 80 years). In the without PSP group, 11 cases of Parkinson disease (PD), 8 cases of multiple system atrophy (MSA), and 4 cases of corticobasal syndrome (CBS) are included. Magnetic resonance Parkinsonism index (MRPI) was used as the MRI index. The ratio between pons and midbrain areas (pons / mid-brain), that between MCP and SCP widths (MCP / SCP), and the MR parkinsonism index ([pons / midbrain] [asterisk] [MCP / SCP]) were calculated. For the ¹²³I-FP-CIT SPECT index, the Specific Binding Ratio (SBR) average was calculated. Then, ROC analysis was performed on the core clinical features, and the diagnostic ability of MRPI and ¹²³I-FP-CIT SPECT in the diagnosis of PSP was evaluated by the comparison of sensitivity, specificity, and accuracy. We also examined the correlation between MRPI and ¹²³I-FP-CIT SPECT.

Results: In regard to the core clinical features, ocular motor dysfunction 15/20 (75.0%) (p <0.0001), postural instability 17/20 (85.0%) (p = 0.077), akinesia 13/20 (65.0%) (p = 0.464) and cognitive dysfunction 5/20 (25.0%) (p = 0.378) were positive for those diagnosed as probable PSP cases. For imaging parameters, the probable PSP patients showed significantly higher MRPI values (14.7±2.9 vs. 8.9± 1.9, p<0.0001) and lower SBR average (2.1 ± 1.3 vs 2.8 ± 1.5, p = 0.061) than the without PSP group. As to the MRPI and SBR average, a significant statistical difference of a negative correlation = -0.289 (p = 0.035) was seen. On calculating the diagnostic ability of the imaging parameters, MRPI (cut-off> 11.6) was 85.0% of sensitivity, 100.0% of specificity, and 94.3% of accuracy. SBR average (cut-off <3.7) was 95.0% of sensitivity, 36.4% of specificity, and 58.5% of accuracy. The reason why the specificity of the SBR average is clearly reduced was thought as being due to the inclusion of 23/33 (69.7%) of disorders (PD, MSA, CBS) in which the SBR average declined in the without PSP group.

Conclusions: ¹²³I-FP-CIT SPECT is an indicator of high sensitivity, and MRI is a highly specific indicator. Since they have complementary roles, it will be possible to perform a more accurate clinical diagnosis of PSP at an earlier stage by properly using these tools.