Substantia nigra echogenicity and imaging of striatal dopamine transporters in Parkinson's disease: A cross-sectional study

Approximately 10% of patients with a presumed diagnosis of Parkinson's disease (PD) remain misdiagnosed despite recent advances in neuroimaging. The current study addresses the use of transcranial sonography and single-photon emission computed tomography (SPECT) using ^99mTc-TRODAT-1 to evaluate the echogenicity of the substantia nigra (SN) and the density of striatal presynaptic dopamine transporters, respectively, in a sample of 20 PD patients (13 males and 7 females) and 9 healthy subjects. The median age of the PD patients was 62 years. The median age at disease onset was 56 years, and the median disease duration was 5 years. The SN echogenic area was larger in PD patients than healthy subjects. The cut-off value of 0.22 cm² for the SN echogenic area was associated with 100% sensitivity and 78% specificity for the diagnosis of PD. Striatal and putaminal ^99mTc-TRODAT-1 binding was lower in PD patients than healthy subjects. The cut-off value of 0.90 for the striatal ^99mTc-TRODAT-1 binding was associated with 100% sensitivity and an 89% specificity for the diagnosis of PD, and the cut-off value of 0.76 for putaminal ^99mTc-TRODAT-1 binding was associated with an 85% sensitivity and an 89% specificity. The size of the SN echogenic area did not correlate with the degree of striatal ^99mTc-TRODAT-1 binding in PD patients. In conclusion, both SN hyperechogenicity and decreased striatal or putaminal ^99mTc-TRODAT-1 binding constitute surrogate markers for differentiating PD patients from healthy individuals with a slightly higher diagnostic specificity of ^99mTc-TRODAT-1 SPECT.