Substantia nigra echogenicity: A structural correlate of functional impairment of the dopaminergic striatal projection in Parkinson's disease

Abstract

Transcranial sonography (TCS) reveals abnormal spatial extension of substantia nigra (SN) echogenicity in a high proportion of patients with Parkinson's disease (PD). It has been proposed that this abnormality represents a structural trait that is mechanistically distinct from degeneration of dopaminergic nigrostriatal projection neurons. We sought to clarify the relationship between sonographic abnormalities of SN and dysfunction of striatal dopaminergic neurotransmission. We studied 50 patients with PD. The spatial extension of the echogenic SN area was compared with the activity of presynaptic striatal dopamine reuptake transporters, assessed in the same patients by I-123-2-beta-carbomethoxy-3-beta-(4-iodophenyl)-tropane (beta-CIT) single-photon emission computed tomography (SPECT). Extension of echogenic SN area correlated (inversely) with striatal activity of presynaptic dopamine reuptake transporter in PD patients (R = -0.417; P = 0.003) and with the equivalent levodopa dose (R = 0.380; P = 0.006; linear regression analysis). Findings support the hypothesis that in PD abnormal extension of echogenic SN area provides a direct structural marker of degeneration of SN neurons. Therefore, in PD, TCS and beta-CIT assess pathophysiologically related phenomena.

Transcranial sonography of the substantia nigra and its correlation with DAT-SPECT in the diagnosis of Parkinson's disease

“…Recent work by Weise D et al [18] found that extension of SN echogenicity correlated with striatal activity of the presynaptic dopaminergic transporter in PD patients, however, another study determined that SN echogenicity remained the same in a 5-year follow up period,…”

Structural abnormality of the substantia nigra in children with attention-deficit hyperactivity disorder

“…Enlarged echogenicity in healthy individuals was associated with impaired uptake of [18F]-dopa in the basal ganglia (assessed by positron emission tomography). 10 Substantia nigra echogenicity was correlated to presynaptic dopaminergic dysfunction elicited by single photon emission computed tomography in patients with Parkinson disease 16 and with the severity of parkinsonism induced by neuroleptics in patients with schizophrenia. 17 However, there is still disagreement about how abnormal extension of substantia nigra echogenicity is related to the pathogenic substrate of Parkinson disease.…”

Place Value of Transcranial Sonography in Early Diagnosis of Parkinson’s Disease

“…Moreover, it has been shown that at least during an observational period of 5 years the area of SN hyperechogenicity does not vary by large [40] , and there does not seem to be correlation of disease progression as evidenced by a reduction in tracer uptake on DATScan examinations and extension of ultrasound signal [6] . Still, the relation of ultrasound signal extension and reduced tracer uptake visualized by different functional neuroimaging techniques deserves further evaluation as results are not consistent [41,42] .…”