title: Risk and protective factors for spasmodic dysphonia: a case-control investigation.
abstract: OBJECTIVE
  Spasmodic dysphonia (SD) is a chronic, incurable, and often disabling voice disorder of unknown pathogenesis. The purpose of this study was to identify possible endogenous and exogenous risk and protective factors uniquely associated with SD.
  
  
  METHODS
  Prospective, exploratory, case-control investigation.
  
  
  METHODS
  One hundred fifty patients with SD and 150 medical controls (MCs) were interviewed regarding their personal and family histories, environmental exposures, illnesses, injuries, voice use patterns, and general health using a previously vetted and validated epidemiologic questionnaire.
  
  
  RESULTS
  Odds ratios and multiple logistic regression analyses (α<0.15) identified several factors that significantly increased the likelihood of having SD. These factors included (1) a personal history of mumps, blepharospasm, tremor, intense occupational and avocational voice use, and a family history of voice disorders; (2) an immediate family history of meningitis, tremor, tics, cancer, and compulsive behaviors; and (3) an extended family history of tremor and cancer.
  
  
  CONCLUSIONS
  SD is likely multifactorial in etiology, involving both genetic and environmental factors. Viral infections/exposures, along with intense voice use, may trigger the onset of SD in genetically predisposed individuals. Future studies should examine the interaction among genetic and environmental factors to determine the pathogenesis of SD.
authors.affiliation: Voice Disorders Center, The University of Utah, Salt Lake City, Utah 84108, USA. kristine.tanner@hsc.utah.edu
authors.forename: Kristine
authors.initials: K
authors.lastname: Tanner
authors.forename: Nelson
authors.initials: N
authors.lastname: Roy
authors.forename: Ray M
authors.initials: RM
authors.lastname: Merrill
authors.forename: Kamille
authors.initials: K
authors.lastname: Kimber
authors.forename: Cara
authors.initials: C
authors.lastname: Sauder
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Houtz
authors.forename: Darrin
authors.initials: D
authors.lastname: Doman
authors.forename: Marshall E
authors.initials: ME
authors.lastname: Smith
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D002908:Chronic Disease; D055154:Dysphonia / Q000453:epidemiology / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011446:Prospective Studies; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D013035:Spasm / Q000503:physiopathology*; D014827:Vocal Cords / Q000503:physiopathology*; D055815:Young Adult