This is helpful and underlines why TCS is not a diagnostic test per se. That doesn't prevent it being a useful tool in seeking support for a diagnosis of PD and a potentially valuable risk marker for PD. There are gender, age and ethnic differences in the adequacy of bone window that can limit some studies findings...
Neurosci Lett. 2014 Sep 9. pii: S0304-3940(14)00736-8. doi: 10.1016/j.neulet.2014.08.053. [Epub ahead of print]
Liu P, Li X, Li FF, Ou-Yang QH, Zhang HX, Feng T.
Abstract
Early and correct diagnosis of Parkinson's disease (PD) is critical for patient counseling and therapeutic management. The diagnostic accuracy of transcranial sonography of substantia nigra (SN-TCS) for early stage PD patients remains controversial. Dopamine transporter (DAT) imaging is sensitive to detect presynaptic dopamine neuronal dysfunction, and has been studied as a diagnostic tool for degenerative parkinsonism. To investigate the predictive value of SN-TCS for the DAT PET scans in clinically diagnosed early stage PD patients, we performed the SN-TCS and DAT Positron Emission Computed Tomography (PET) Imaging examinations on 53 patients. Using the DAT PET results as clinical gold standard, the sensitivity and specificity of TCS was 68.75% and 40% respectively. The positive predictive value (PPV) of an abnormal TCS for an abnormal PET scan was 91.67%. However, the negative predictive value (NPV) for a normal PET scan was only 11.76%. The false negative rate was 31.25%. In 35 patients, the result of the SN-TCD was in accordance with the result of the DAT PET scan (Kappa=0.042, P>0.05). The consistency between SN-TCS and PET scans was poor. We conclude that SN-TCS would not be used as a diagnostic tool for early stage PD patients. Negative result of TCS could not exclude the diagnosis of PD. Further tests like DAT-PET is needed for validation. On the other hand, positive SN-TCS will reduce the added diagnostic value of a presynaptic neuronimaging scan.
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