Transcranial sonography in atypical parkinsonism: How reliable is it in real clinical practice? A multicentre comprehensive study

Introduction Substantia nigra hyperechogenicity (SN+) in transcranial sonography (TCS) is frequent in Parkinson's disease (PD), while lenticular nucleus hyperechogenicity (LN+) and 3rd ventricle enlargement (3V+) are typical of Atypical Parkinsonisms (AP). However, there are no studies assessing the diagnostic yield of all TCS biomarkers in the three AP (progressive supranuclear palsy, PSP, multiple system atrophy, MSA, corticobasal degeneration, CBD). Previous references lack homogeneous criteria and data are incomprehensive. Methods Analysis of TCS performed in routine clinical practice in AP and PD patients from two tertiary hospitals. Expert recommendations were strictly followed. Previous literature was critically analysed. Results 155 AP (98 PSP, 40 MSA, 14 CBD), 254 PD, 145 control subjects were included. We confirmed good sensitivity for SN+ in PD (80%), but specificity was lower than reported (61%). LN+ and 3V + had moderate sensitivity for AP and PSP diagnosis respectively (65%, 63%), but specificity was higher than reported (87%, 91%). We confirmed high specificity and positive predictive value of the combination SN/LN (98%, 93% AP; 83%, 86% PD). The combinations of two or three echofeatures, previously unreported, showed high specificity but lower sensitivity (SN/3V: 75% sensitivity, 87% specificity PD; 42% sensitivity, 98% specificity PSP) (SN + LN+: 79% sensitivity, 86% specificity CBD) (SN/3V/LN: 67% sensitivity, 89% specificity PD; 29% sensitivity, 99% specificity PSP; 41% sensitivity, 95% specificity MSA; 57% sensitivity 91% specificity CBD). Conclusions We present a large comprehensive study of TCS, confirming its usefulness and certain limitations in AP diagnosis. Adherence to consensus criteria is critical to implement TCS for clinical and research purposes.