Objective: To (1) evaluate a new coronal examination plane in comparison to the established axial examination plane for detection of nigral hyperechogenicity and (2) to evaluate an additional M-mode tremor frequency determination (M-TFD) for differentiation of idiopathic Parkinson´s disease (IPD) and essential tremor (ET).

Background: Transcranial sonography (TCS) is an established and sensitive diagnostic tool for the differentiation of IPD and ET. In current practice, a single axial mesencephalic examination plane is used for the quantification of substantia nigra (SN) hyperechogenicity, which is often present in IPS but rarely in ET. However, the SN can also be depicted in a second coronal examination plane, whose diagnostic value has not yet been evaluated in detail. Furthermore, the M-mode tremor frequency determination (M-TFD) represents another sonographic examination tool, which might yield additional diagnostic value.

Methods: Echogenic areas of the SN of 30 PD patients, 7 ET patients and 13 healthy controls were determined by TCS in axial and coronal planes. In both planes a cut-off-value ≥ 0,2cm² was used to define SN-hyperechogenicity (SN+). Tremor frequencies of resting and postural tremor were quantified by a M-TFD examination protocol. Isolated postural tremor with a frequency ≥ 6Hz was defined as a typical ET-finding.

Results: The axial plane TCS protocol showed a sensitivity of 90%, a specificity of 80%, a positive predictive value (PPV) of 87% and a negative predictive value (NPV) of 84% in supporting the diagnosis of PD. Interestingly, the use of the new coronal examination plane revealed even superior values (sensitivity=93%, specificity=85%, PPV=90%, NPV=89%). The combined sonographic assessment of TCS and M-TFD provided best diagnostic strength (sensitivity=90%, specificity=95%, PPV=96%, NPV=86%).

Conclusions: In the present study, the utilization of a coronal examination plane improved the diagnostic strength of TCS in discriminating IPD from ET. In combination with determination of tremor frequency by M-TFD best discriminative results were achieved. Thus, the combined usage of coronal TCS and M-TFD should be considered in the future to optimally apply sonography techniques for the differentiation of IPD and ET.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/diagnostic-value-of-a-new-coronal-examination-plane-in-transcranial-nigral-sonography-and-of-additional-m-mode-tremor-frequency-determination-for-the-differentiation-of-idiopathic-parkinsons-disease/