Combination of olfactory test and substantia nigra transcranial sonopraphy in the differential diagnosis of Parkinson’s disease: a pilot study from China

OBJECTIVES: Both hyposmia and substania nigra (SN) hyperechogenicity on trascranial sonography (TCS) were risk markers for idiopathic Parkinson’s disease (PD), which was beneficial to the differential diagnosis of the disease. However, each of their single diagnostic value is often limited. The purpose of present study was to explore whether the combination of olfactory test and TCS of SN could enhance the differential diagnostic power in Chinese patients with PD. METHODS: Thirty-seven patients with PD and twenty-six patients with essential tremor (ET) were evaluated on 16-item odor identification test from extended version of sniffin’ sticks and TCS of SN. The frequency of hyposmia and SN hyperechogenicity in each group was compared. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the two clinical biomarkers were analyzed. RESULTS: The frequency of hyposmia in patients with PD was significantly higher than in patients with ET (62.2% VS. 3.8%, P = 0.000). The frequency of SN hyperechogenicity in patients with PD was significantly higher than in ET subjects (48.6% VS. 15.4%, P = 0.006). The combination of hyposmia and SN hyperechogenicity (if either one or both present) discriminated patients with PD from ET with a sensitivity of 78.4% and 29.7%, specificity of 80.8% and 100%, PPV of 85.3% and 100%, and NPV of 72.4% and 50.0%, respectively. CONCLUSIONS: Our preliminary data suggested that the combination of hyposmia and SN hyperechogenicity could improve the diagnostic potential for discriminating Chinese patients with PD from ET.