Potential PD biomarkers identified for sleep behavior disorder

By Lucy Piper, Senior MedWire Reporter

Concomitant olfaction abnormality and increased substantia nigra (SN) echogenicity may be preclinical manifestations of parkinsonism in patients with idiopathic rapid eye movement sleep behavior disorder (iRBD), research suggests.

Jin Whan Cho (Sungkyunkwan University School of Medicine, Seoul, Korea) and colleagues found that this combination was frequently observed in patients with Parkinson's disease (PD) and those with iRBD compared with healthy individuals, at a respective 75% and 50% versus 3%.

They report in Neurological Sciences that "the olfactory dysfunction and SN hyperechogenicity could be an early noninvasive biomarker of PD [Parkinson's disease] in iRBD patients."

However, longitudinal study in their patients will be needed to confirm this.

The team used the cross-cultural smell identification test to assess olfactory function in 15 patients with iRBD, as confirmed by polysomnography, 30 patients with PD, and 30 healthy controls.

Test scores were similar in patients with iRBD and PD, at an average of 7.1 and 7.6 versus 10.4 in controls, respectively.

Indeed, olfactory deficits, including hyposmia or anosmia, were more common in the patients with iRBD (93.3%) and PD (86.7%), compared with controls (53.3%). Only one patient in the iRBD group was able to differentiate between odors normally, the team notes.

Midbrain transcranial sonography [TCS] carried out in the same groups of patients showed that the sum of bilateral SN echosignals was increased in patients with iRBD, compared with controls, but not to the extent seen in patients with PD, at 0.29 cm2, 0.11 cm2, and 0.72 cm2, respectively.

The frequency of abnormal increased SN echogenicity was 50.0% in iRBD patients, 16.0% in controls, and 87.5% in PD patients.

These findings are consistent with those of other researchers, who have suggested that olfactory dysfunction and SN echogenicity are associated with neuronal degeneration, progressing from the subceruleus region to the midbrain in the case of PD following iRBD.

"However, few [studies] investigated the concomitant olfactory dysfunction and TCS in iRBD patients," they note.

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