The role of substantia nigra sonography in the differentiation of Parkinson's disease and multiple system atrophy.
Background
The differential diagnosis of Parkinson's disease (PD) and multiple system atrophy (MSA) remains a challenge, especially in the early stage. Here, we assessed the value of transcranial sonography (TCS) to discriminate non-tremor dominant (non-TD) PD from MSA with predominant parkinsonism (MSA-P).


Methods
Eighty-six MSA-P patients and 147 age and gender-matched non-TD PD patients who had appropriate temporal acoustic bone windows were included in this study. All the patients were followed up for at least 2 years to confirm the initial diagnosis. Patients with at least one substantia nigra (SN) echogenic size ≥18 mm2 were classified as hyperechogenic, those with at least one SN echogenic size ≥25 mm2 was defined as markedly hyperechogenic.


Results
The frequency of SN hyperechogenicity in non-TD PD patients was significantly higher than that in MSA-P patients (74.1% vs. 38.4%, p <  0.001). SN hyperechogenicity discriminated non-TD PD from MSA-P with sensitivity of 74.1%, specificity of 61.6%, and positive predictive value of 76.8%. If marked SN hyperechogenicity was used as the cutoff value (≥ 25 mm2), the sensitivity decreased to 46.3%, but the specificity and positive predictive value increased to 80.2 and 80.0%. Additionally, in those patients with SN hyperechogenicity, positive correlation between SN hyperechogenicity area and disease duration was found in non-TD PD rather than in MSA-P patients. In this context, among early-stage patients with disease duration ≤3 years, the sensitivity, specificity and positive predictive value of SN hyperechogenicity further declined to 69.8%, 52.2%, and 66.7%, respectively.


Conclusions
TCS could help discriminate non-TD PD from MSA-P in a certain extent, but the limitation was also obvious with relatively low specificity, especially in the early stage.
['Zhou|Hai-Yan|HY|', 'Huang|Pei|P|0000-0002-1593-1516', 'Sun|Qian|Q|', 'Du|Juan-Juan|JJ|', 'Cui|Shi-Shuang|SS|', 'Hu|Yun-Yun|YY|', 'Zhan|Wei-Wei|WW|', 'Wang|Ying|Y|', 'Xiao|Qin|Q|', 'Liu|Jun|J|', 'Tan|Yu-Yan|YY|', 'Chen|Sheng-Di|SD|']
Substantia nigra Multiple system atrophy Transcranial sonography Disease duration Atypical parkinsonian disorders Parkinson’s disease