Abstract
Hyperechogenicity of the substantia nigra on transcranial sonography is used for diagnosing Parkinson disease (PD). Cutoff values for the substantia nigra echogenic area, defining substantia nigra hyperechogenicity, vary among ultrasound systems from different manufacturers. In this study we wanted to determine the cutoff criterion for a Toshiba (Tokyo, Japan) system and to assess its diagnostic value. Three hundred participants (controls, n = 138; patients with PD, n = 105; and patients with essential tremor, n = 57) underwent transcranial sonography following a standardized protocol. The substantia nigra was assessable in 92.7% of all participants. The substantia nigra echogenic area (larger of bilateral measurements) was larger in patients with PD (mean ± SD, 0.24 ± 0.05 cm(2)) than controls (0.14 ± 0.05 cm(2); P < .001) and patients with essential tremor (0.14 ± 0.04 cm(2); P < .001). Substantia nigra echogenicity was larger in male participants (0.20 ± 0.07 cm(2)) than female participants (0.15 ± 0.06 cm(2); P< .001). Age did not correlate with substantia nigra echogenicity in any group. Frontal horn width was larger and lenticular nucleus hyperechogenicity and a discontinuous raphe were more frequent in the PD group than the other groups. On multivariate analysis, only substantia nigra hyperechogenicity was associated with the diagnosis of PD. The 90th-percentile substantia nigra echogenic area in the control group, which defined marked substantia nigra hyperechogenicity, also represented the optimum cutoff value for discrimination of PD from non-PD participants on receiver operating characteristic curve analysis (area under the curve, 0.913; Youden index, 0.73). This cutoff value (≥0.21 cm(2), larger of bilateral measurements) yielded sensitivity of 83% and specificity of 90% for the diagnosis of PD. Transcranial sonography shows good diagnostic validity for diagnosis of PD when implemented according to a strictly standardized protocol.
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