title: Olfactory dysfunction in Multiple Sclerosis: A scoping review of the literature.
abstract: OBJECTIVE
  Olfactory dysfunction in Multiple Sclerosis (MS) has been reported, but results have been inconsistent. In this review we describe, synthesize, and interpret the existing literature on olfactory dysfunction in Multiple Sclerosis and identify gaps in the current level of knowledge.
  
  
  METHODS
  The study design was a scoping review of the literature covering several study designs. Systematic Searches of the PubMed, CINAHL, Cochrane Library, Web of Science, PsycARTICLES, PsycINFO and Google Scholar databases were conducted that included key words related to Multiple Sclerosis and Olfaction Disorders. Literature that met the criteria of pertaining to both Multiple Sclerosis and olfactory dysfunction was identified, with the aim of providing an overview of the extent and types of research available in this area.
  
  
  RESULTS
  Sixty-one reports were identified in the initial search, with 40 meeting the study criteria. Twenty-five clinical studies were included. Among them, 23 studies measured for olfactory dysfunction in MS patients, ten evaluated MRI correlates of olfactory dysfunction, and five evaluated neurophysiology correlates of olfactory dysfunction. Six of the included studies were abstracts. In addition, thirteen reviews/commentaries and two case studies were included. The majority of the studies identified some degree of olfactory dysfunction in MS patients, and various aspects and correlations with olfactory impairment were observed.
  
  
  CONCLUSIONS
  The overall weight of the literature suggests that olfactory dysfunction may occur in MS. Although there is variability in reported frequency, the more robust studies suggest the prevalence is significant, ranging from 20% to 45% in the MS population. Despite this, the mechanisms are unknown and the clinical relevance of this association has not been well explored. Interesting findings relating mood disorders, cognition, and olfactory dysfunction in MS are also suggested but remain poorly developed and require further investigation. Future studies are also warranted to understand the dynamic changes in olfactory function during the course of MS, and to correlate olfactory function with relapses/disease activity.
authors.affiliation: Departments of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA. Electronic address: elucassen@hmc.psu.edu.
authors.forename: Elisabeth B
authors.initials: EB
authors.lastname: Lucassen
authors.affiliation: Departments of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Turel
authors.affiliation: George T. Harrell Health Sciences Library, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Knehans
authors.affiliation: Departments of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Pharmacology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Radiology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Neurosurgery, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Kinesiology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Huang
authors.affiliation: Departments of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Eslinger
mesh_terms: D006801:Humans; D009103:Multiple Sclerosis / Q000503:physiopathology*; D000857:Olfaction Disorders / Q000503:physiopathology*
keywords: Demyelination; Multiple Sclerosis; Olfaction Disorders; Olfactory; Olfactory dysfunction; Smell