title: A systematic review and meta-analysis on acoustic voice parameters after uncomplicated thyroidectomy.
abstract: BACKGROUND
  Postthyroidectomy voice changes are common even without apparent laryngeal nerve injury. Our study evaluated the impact of open cervical thyroidectomy on five acoustic voice parameters in the early (< 3 months) and late (≥ 3 months) postoperative periods.
  
  
  METHODS
  A systematic review was performed to identify studies that quantitatively assessed voice quality by acoustic voice analysis before and after thyroidectomy. Parameters included average fundamental frequency (F0 , Hz), jitter (%), shimmer (%), noise-to-harmonic ratio (NHR), and maximum phonation time (MPT) (in secs). Meta-analysis was performed using both fixed- and random-effects models.
  
  
  RESULTS
  A total of 896 patients were analyzed. Relative to baseline, F0 significantly worsened in the early period (from 194.9 ± 34.9 Hz to 188.0 ± 34.0 Hz, P = 0.001). This was equivalent to a quarter-tone loss (P = 0.004). Shimmer (from 3.15 ± 1.59% to 3.19 ± 1.70%, P = 0.040) and MPT (from 17.9 secs to 16.7 secs, P = 0.046) also worsened in the early period, whereas jitter and NHR remained unchanged in the early and late periods. Males suffered greater deterioration in F0 (from 120.6 ± 18.8 Hz to 111.0 ± 18.5 Hz, P = 0.048) and in NHR (from 0.12 ± 0.02 to 0.16 ± 0.03, P = 0.019) than females in the early period. Four of the five acoustic parameters (F0 , jitter, shimmer, and NHR) significantly worsened after total thyroidectomy (TT) and not after lesser resection.
  
  
  CONCLUSIONS
  F0 , shimmer, and MPT significantly worsened in the early and not in the late postoperative period. F0 impairment was perceptually significant. Males and those undergoing TT suffered greater voice impairment than their counterparts during the early period.
authors.affiliation: Department of Surgery.
authors.forename: Brian H H
authors.initials: BH
authors.lastname: Lang
authors.affiliation: Department of Family Medicine and Primary Care, 3/F Ap Lei Chau Clinic.
authors.forename: Carlos K H
authors.initials: CK
authors.lastname: Wong
authors.affiliation: Division of Speech and Hearing Sciences, the University of Hong Kong, Hong Kong SAR, the People's Republic of China.
authors.forename: Estella P M
authors.initials: EP
authors.lastname: Ma
mesh_terms: D000162:Acoustics; D005260:Female; D006801:Humans; D008297:Male; D011184:Postoperative Period; D013965:Thyroidectomy; D014831:Voice / Q000502:physiology*; D014832:Voice Disorders / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D014833:Voice Quality
keywords: Thyroidectomy; acoustic analysis; dysphonia; recurrent laryngeal nerve; voice