Substantia nigra hyperechogenicity in Parkinson’s disease

Abstract

Dear Editor Over the past 15 years, the visualization of brain structures, mainly the mesencephalon and the basal ganglia, has been possible by transcranial sonography (TCS) in patients with intact skull. Since then, several papers concerning TCS in movement disorders have been published, nevertheless, to the best of our knowledge, none of them in neurosurgical journals. In order to update the neurosurgical community on this subject, the authors report a characteristic finding of Parkinson’s disease (PD), the hyperechogenicity of the substantia nigra (SN) disclosed by TCS [1–10, 12], and discuss the significance of this ultrasound sign in clinical neurosurgery. A 59-year-old man with advanced PD, severe motor fluctuations, and incapacitating levodopa-induced dyskinesias underwent bilateral deep brain stimulation (DBS) of the subthalamic nucleus with excellent results. He presented with a relatively early onset of PD symptoms (50 years of age). Transcranial brain sonography disclosed a marked hyperechogenicity of the SN (0.36 cm on the right SN, and 0.39 cm on the opposite side; Fig. 1a), and a normal echogenicity lentiform nucleus. Hyperechogenic images of the DBS electrodes were also shown clearly (Fig. 1b). SN hyperechogenicity has been considered characteristic for idiopathic PD, occurring in 91-100% of the patients [3, 8]. It was demonstrated to be caused by increased amounts of iron bound to protein other than ferritin in the SN, and reflects a functional impairment of the nigrostriatal dopaminergic system [2, 7]. For most authors, echogenic areas in the SN region ≤0.19 cm are classified as normal, while areas ≥0.20 cm are considered as hyperechogenic [1–10, 12]. SN echogenic size tends to be larger contralateral to the clinically more affected side, and larger SN echogenic sizes correlate with younger age at the disease onset [3, 8]. The diagnosis of PD is a challenge since several other conditions resemble the idiopathic form of the disease. SN hyperechogenicity associated with normal lentiform nucleus echogenicity may discriminate idiopathic PD from atypical Parkinsonian syndromes (multiple system atrophy and progressive supranuclear palsy) with a positive predictive value ≥90% [3, 8, 9]. In a prospective blinded study, the sensitivity of SN hyperechogenicity for idiopathic PD versus atypical Parkinsonian syndromes was 94.8%, the specificity was 90%, the positive predictive value was 97.4%, and the negative predictive value was 81.8% [4]. In asymptomatic adult subjects, SN hyperechogenicity, at least unilaterally, indicates a subclinical functional impairment of the nigrostriatal dopaminergic system. Recent papers revealed that SN hyperechogenicity might suggest preclinical PD [2, 3, 7, 8], and SN hyperechogenicity correlates with severity of Parkinsonian symptoms induced by neuroleptic therapy [1]. Reduced echogenicity of midbrain raphe indicates increased risk of depression and urinary incontinence in PD patients. Caudate nucleus hyperechogenicity is associE. Bor-Seng-Shu (*) :M. J. Teixeira Division of Neurological Surgery, Laboratory for Neurosonology, Cerebral Hemodynamics and Neurocritical Care, Hospital das Clinicas, University of Sao Paulo School of Medicine, Rua Loefgreen, 1272, CEP 04040-001 Sao Paulo, Brazil e-mail: edsonshu@hotmail.com