Transcranial imaging of substantia nigra hyperechogenicity in a Taiwanese cohort of Parkinson's disease

Abstract

Transcranial Doppler imaging (TCDI) has been used as a noninvasive diagnostic tool to differentiate Parkinson's disease (PD) from atypical parkinsonism by detecting hyperechogenicity in the substantia nigra (SN). To our knowledge, no TCDI data are available for Asian populations, and TCDI sensitivity is uncertain across populations. Early-onset PD (EOPD) represents a specific PD subtype based on clinical features and pathogenic mechanisms. It is not known if EOPD patients have abnormal echogenicity in SN comparable to late-onset PD (LOPD) patients. We assessed the area of SN hyperechogenicity (hyper-SN) and a ratio of hyper-SN over ipsilateral midbrain (S/M ratio) with TCDI in 164 healthy Taiwanese, 40 EOPD patients, and 40 LOPD patients. The upper 95th percentile values for hyper-SN and S/M ratio were 0.20 cm(2) and 0.07. Our results indicate that S/M ratio is a more sensitive measure than hyper-SN in diagnosing PD. Approximately 92.5% of the LOPD patients and 57.5% of the EOPD patients had S/M ratios >/= 0.07. Enlarged hyperechogenicity of SN is a common finding in LOPD, but not in EOPD. Iron-independent mechanisms of SN cell degeneration in EOPD distinct from that in LOPD might contribute to the sonographic findings.