title: Seasonal Difference in Postthyroidectomy Hypocalcemia: A Montreal-Based Study.
abstract: OBJECTIVE
  Hypocalcemia following thyroidectomy often prolongs hospital stay and is potentially life-threatening. The objective of this study is to determine whether the season when thyroidectomy is performed is associated with postoperative hypocalcemia.
  
  
  METHODS
  Retrospective case series of patients undergoing thyroid surgery from 2009 to 2015.
  
  
  METHODS
  Tertiary care academic institution in Montreal, Canada.
  
  
  METHODS
  A consecutive sample of 823 patients undergoing thyroidectomy by a single high-volume otolaryngologist for a suspected or confirmed thyroid malignancy. Patient demographics, procedure type, calcium and vitamin D supplementation, and seasonal rate of hypocalcemia postthyroidectomy were calculated and compared.
  
  
  RESULTS
  Average seasonal rates of postthyroidectomy hypocalcemia in the winter, spring, summer, and autumn were, respectively, 8.3% (8 of 216), 7.3% (12 of 165), 1.5% (3 of 201), and 3.5% (8 of 228; P < .005). Patients operated in the winter were 5.6 times more likely to develop hypocalcemia as compared with those in the summer (P < .01; 95% confidence interval: 1.7-18.7). In a multiple regression analysis factoring in season when surgery was performed, procedure type, and preoperative vitamin D/calcium supplementation, surgery occurring in the winter predicted a hypocalcemia event (correlation coefficient [SE]: 0.72 [0.024], P = .026; 0.006 [0.025], P = .81; 0.004 [0.019], P = .82, respectively).
  
  
  CONCLUSIONS
  In this study, patients undergoing thyroidectomy in the winter months were more likely to develop postoperative hypocalcemia when compared with those operated in the summer. Further studies are needed to understand the role of vitamin D in the observed seasonal difference in hypocalcemia rates.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, McGill University Health Center, Montreal, Canada marco.mascarella@mail.mcgill.ca.
authors.forename: Marco A
authors.initials: MA
authors.lastname: Mascarella
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, McGill University Health Center, Montreal, Canada.
authors.forename: Véronique-Isabelle
authors.initials: VI
authors.lastname: Forest
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, McGill University Health Center, Montreal, Canada.
authors.forename: Carol
authors.initials: C
authors.lastname: Nhan
authors.affiliation: Department of Endocrinology, University de Montreal, Notre Dame Hospital, Montreal, Canada.
authors.forename: Rébecca
authors.initials: R
authors.lastname: Leboeuf
authors.affiliation: Division of Endocrinology and Metabolism, Jewish General Hospital, Montreal, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Tamilia
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, McGill University Health Center, Montreal, Canada.
authors.forename: Alex M
authors.initials: AM
authors.lastname: Mlynarek
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, McGill University Health Center, Montreal, Canada.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Payne
mesh_terms: D002118:Calcium / Q000097:blood; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006996:Hypocalcemia / Q000097:blood / Q000453:epidemiology* / Q000209:etiology; D015994:Incidence; D007902:Length of Stay / Q000639:trends; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications; D011184:Postoperative Period; D011792:Quebec / Q000453:epidemiology; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D013965:Thyroidectomy / Q000009:adverse effects*
chemical_list: D002118:Calcium
keywords: hypocalcemia; seasonal variation; thyroidectomy