title: Residual thyroid tissue after thyroidectomy in a patient with TSH receptor-activating mutation presenting as a neck mass.
abstract: BACKGROUND
  Activating mutations of the TSH receptor (TSHR) are rare, with few reported cases of long-term follow-up.
  
  
  METHODS
  We present a follow-up report on a patient with neonatal thyrotoxicosis known to have a rare activating mutation of the TSHR, a heterozygous substitution in exon 10 (p.Ile568Thr). Initial treatment included total thyroidectomy at age 2 ½ years, resulting in iatrogenic hypothyroidism and hypoparathyroidism. The patient was treated with levothyroxine replacement to maintain TSH levels within normal range, as well as calcitriol and calcium carbonate to treat postsurgical hypoparathyroidism. However, 4 years later, while euthyroid, he developed a palpable 1-cm midline neck mass.
  
  
  RESULTS
  Functional imaging with 123-I thyroid scan demonstrated active thyroid tissue within the thyroglossal duct remnant and in the tracheoesophageal groove. Surgical removal of the neck mass revealed cytologically bland thyroid follicular cells.
  
  
  CONCLUSIONS
  These findings suggest that even after total thyroidectomy, patients with TSHR-activating mutations are at risk to develop significant quantities of functional thyroid tissue related to the hypertrophy of residual foci in the thyroid bed and in the thyroglossal duct remnant. These residual foci may enlarge and secrete thyroid hormones autonomously, decreasing the patient's levothyroxine requirement. Surveillance with serial physical examination and biochemical monitoring is recommended; suspicious findings can be further evaluated with functional thyroid imaging (99-m technetium or radioiodine 123-I thyroid scans) to adequately identify residual foci of thyroid tissue, which may require further treatment with surgical excision or radioablation.
authors.affiliation: Division of Pediatric Endocrinology, Department of Pediatrics, University of Michigan, Ann Arbor, Michigan 48109, USA. ksinger@umich.edu
authors.forename: Kanakadurga
authors.initials: K
authors.lastname: Singer
authors.forename: Ram K
authors.initials: RK
authors.lastname: Menon
authors.forename: Marci M
authors.initials: MM
authors.lastname: Lesperance
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: McHugh
authors.forename: Stephen S
authors.initials: SS
authors.lastname: Gebarski
authors.forename: Anca M
authors.initials: AM
authors.lastname: Avram
mesh_terms: D002648:Child; D006801:Humans; D008297:Male; D009154:Mutation; D011989:Receptors, Thyrotropin / Q000235:genetics*; D013961:Thyroid Gland / Q000473:pathology / Q000601:surgery*; D016606:Thyroid Nodule / Q000235:genetics / Q000473:pathology / Q000601:surgery*; D013965:Thyroidectomy
chemical_list: D011989:Receptors, Thyrotropin