[Sonography of the parenchyma in Parkinson's disease].

Transcranial sonography (TCS) of the brain parenchyma is a non-invasive and easily applicable neuroimaging technique which is used as a diagnostic tool in Parkinson's disease. Up to 90% of patients with idiopathic Parkinson's disease but only 10-15% of the healthy population show an abnormal echogenicity (hyperechogenicity) of the substantia nigra (SN). TCS has been demonstrated to be a useful tool in the differential diagnosis of patients with essential tremor or atypical parkinsonian syndromes, including the parkinsonian variant of multiple system atrophy (MSA-P) and progressive supranuclear palsy (PSP) where hyperechogenicity of the SN is less frequent. Abnormal echogenicity of the SN has been found in almost all investigated monogenic types of parkinsonism and even in asymptomatic mutation carriers. The nature of the pathological substrate leading to the abnormal echogenicity of the SN remains elusive. Longitudinal studies of asymptomatic subjects with abnormal echogenicity of the SN are still ongoing to evaluate the risk for developing Parkinson's disease in the future in these subjects.