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Brief description/objective

Objective: The aim of the study was to investigate whether there is an association between hyperechogenicity and olfactory function in patients with iRBD.
Background: Recent studies have reported an increased risk to develop Parkinson’s disease (PD) in patients with idiopathic REM sleep behavior disorder (iRBD). Midbrain hyperechogenicity is a common transcranial sonography (TCS) finding in PD and has been suggested as a PD risk-marker in nonparkinsonian subjects. Further, in several studies olfactory dysfunction has shown to be a potential non-motor antecedents of PD.
Methods: 31 patients from the sleep centers of the Medical University
of Innsbruck, Austria (n521), and the Hospital Clinic de Barcelona,
Spain (n510), with a diagnosis of iRBD were included in this study. All patients underwent a TCS investigation from both sides using the temporal approach to display the butterfly-shaped mesencephalon and the echogenic signal in the area of the substantia nigra. Olfactory testing was performed using the Sniffin sticks battery including testing of odour identification, discrimination and threshold.
Results: 66% (n518) of the iRBD patients showed an impaired olfactory function and 39% (n511) were found to have midbrain hyperechogenicity. There was no significant difference in the results of the Sniffin stick test between patients with midbrain hyperechogenicity and those without. Statistical analysis did not reveal any significant association between midbrain hyperechogenicity and olfactory dysfunction.
Conclusions: In this study there is no association between midbrain
hyperechogenicity and impaired olfactory function in patients with iRBD. Due to the small population of patients, a beta-error cannot definitely be excluded. Further studies in larger iRBD samples are needed to determine if hyposmia and midbrain hyperechogenicity are independent risk markers for developing PD in patients with iRBD.