Substantia nigra hyperechogenicity in essential tremor and Parkinson's disease: a longitudinal study

Abstract

Background and purpose Essential tremor (ET) and Parkinson's disease (PD) sometimes overlap in their clinical expression with ET preceding PD onset, often leading to misdiagnosis. Transcranial sonography (TCS) has been shown to be a valid and non‐invasive diagnostic tool to identify early idiopathic PD and to differentiate it from ET. The purpose of this study was to investigate the relevance of substantia nigra hyperechogenicity in patients with ET. Methods A total of 138 patients (79 with PD, 59 with ET) and 50 matched controls underwent TCS examination at baseline. All patients were followed in a 3‐year longitudinal assessment. Results A total of 10 subjects were excluded from the analysis due to the bilateral absence of a temporal acoustic window. During the follow‐up period, 11 of the patients with ET developed new‐onset parkinsonian features, without fulfilling criteria for PD diagnosis (ET+). Nine patients developed clinical features meeting diagnostic criteria for probable PD (ET‐PD). Patients with ET− did not develop parkinsonian features. For each group, the maximum size of the substantia nigra hyperechogenicity was as follows: 5.62 ± 5.40 mm2 in the control group, 19.02 ± 14.27 mm2 in patients with PD, 9.15 ± 11.26 mm2 in patients with ET−, 20.05 ± 13.78 mm2 in patients with ET+ and 20.13 ± 13.51 mm2 in patients with ET‐PD. ET‐PD maximum values were significantly different from controls. Maximum values in patients with ET+ were different from both controls and patients with ET−. Conclusion Substantia nigra hyperechogenicity in ET seems to represent a risk marker for developing early parkinsonian symptoms or signs in the 3 years following TCS assessment.

Differentiating Parkinson’s Disease from Essential Tremor Using Transcranial Sonography: A Systematic Review and Meta-Analysis

“…After review of the abstracts, 46 publications were selected. Eighteen studies satisfied the predefined criteria and were assessed [ 12–29 ]. A detailed flow chart of the review process is shown in Fig.…”

“…All studies only included patients with sufficient temporal bone window in the final analysis. All studies except of two [ 14, 26 ] used established criteria for PD and ET as a reference standard, albeit the criteria used are not consistent between the studies: For PD diagnosis, two studies [ 12, 24 ] used the MDS clinical diagnostic criteria [ 30 ], thirteen studies [ 13–20, 23, 25, 27–29 ] used the UK Brain Bank Criteria [ 31, 32 ], two studies [ 21, 22 ] used the Gelb et al. criteria [ 33 ], and one study did not explicitly state which criteria for PD diagnosis were used [ 26 ].…”

“…For two studies, abnormal presynaptic dopaminergic terminal radiotracer-imaging as assessed with DaTSCAN was an inclusion criterion for patients with PD [ 25, 26 ]. For ET diagnosis, ten studies [ 12, 15–19, 23–25, 28 ] used the Consensus statement of the Movement Disorder Society on Tremor [ 34 ], four studies [ 13, 20, 27, 29 ] used criteria for the diagnosis of essential tremor [ 35 ], two studies [ 21, 22 ] used the diagnostic criteria for essential tremor [ 36 ], and two studies [ 14, 26 ] did not explicitly state which criteria were used.…”

“…Interrater agreement was given in four studies and has shown to be very good in all studies [ 16, 17, 24, 25 ]. Six studies [ 12, 15, 20, 22, 25, 26 ] conducted DaTSCAN as well, but only three of the included studies [ 20, 22, 25 ] compared TCS and DaTSCAN results for differentiation between PD and ET, the other three studies used an abnormal DaTSCAN result as an inclusion criterion for PD patients.…”

Neuroimaging Advances in Parkinson's Disease and Atypical Parkinsonian Syndromes

“…It is also important to note that ∼10% of healthy controls, as well as ∼16% of patients with essential tremor may show elevated echogenicity in the SN (190), thus limiting the utility of this "echofeature" as a standalone biomarker of PD. For example, in a 3 year longitudinal study, baseline SN hyperechogenicity was evident not only in PD, but also in patients with essential tremor, who subsequently developed parkinsonian symptoms during the follow-up period (191).…”