The combined effect of REM sleep behavior disorder and hyposmia on cognition and motor phenotype in Parkinson's disease

Aug 20, 2016Journal of the neurological sciences

How sleep movement disorder and reduced sense of smell together relate to thinking and movement symptoms in Parkinson’s disease

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Abstract

Patients with both REM sleep behavior disorder and olfactory dysfunction had lower cognitive performance scores.

Olfactory function was assessed using the Cross Cultural Smell Identification Test.
Cognitive performance was evaluated with the Mini-Mental State Examination, showing significant differences based on olfactory status.
The presence of both REM sleep behavior disorder and olfactory dysfunction correlated with poorer cognitive function.
Patients with both conditions were more likely to present with the akinetic-rigid type of Parkinson's disease.
There was a notable distinction in olfactory dysfunction and REM sleep behavior disorder across different motor phenotypes of Parkinson's disease.

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BACKGROUND: Olfactory dysfunction and REM sleep behavior disorder (RBD) are recognized as pre-motor symptoms of Parkinson's disease (PD). Cognitive dysfunction is observed at a high rate even in the early stages of PD as an important non-motor symptom. PD has been classified in different subtypes and it is unknown if olfactory dysfunction and RBD occur more often in one particular subtype. We investigated the relationship between olfactory impairment, RBD, initial cognitive performance and motor phenotype in PD.

METHOD: Nighty-eight patients with drug-naïve idiopathic PD who visited the Movement Disorders Unit of Korea University Guro Hospital, Seoul, Korea from March 2012 to February 2014 were retrospectively included. Patients were divided into tremor-dominant-type and akinetic-rigid-type PD subgroups using part III of the Unified Parkinson's Disease Rating Scale. Olfaction was assessed by the Cross Cultural Smell Identification Test. RBD was screened using screening questionnaires. Initial cognitive function was assessed with Mini-Mental State Examination.

RESULT: The PD-normosmia group had higher MMSE scores (p=0.008). PD patients who have both RBD and olfactory dysfunction had lower MMSE scores (p=0.013). Presence of both RBD and hyposmia in PD patients was more strongly correlated with poor cognitive dysfunction. PD patients with RBD and/or hyposmia primarily exhibited the akinetic-rigidity phenotype.

CONCLUSION: Olfactory dysfunction and RBD differed according to the motor phenotypes of PD. This suggests that olfactory dysfunction and RBD might relate to prognosis in patients with PD. Patients who have both hyposmia and RBD were more likely to exhibit cognitive dysfunction.

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The combined effect of REM sleep behavior disorder and hyposmia on cognition and motor phenotype in Parkinson's disease

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