title: Does the intensity of diffuse thyroid gland uptake on F-18 fluorodeoxyglucose positron emission tomography/computed tomography scan predict the severity of hypothyroidism? Correlation between maximal standardized uptake value and serum thyroid stimulating hormone levels.
abstract: BACKGROUND
  F-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography/computed tomography (PET/CT) scan and hypothyroidism.
  
  
  OBJECTIVE
  The aim was to determine whether the intensity of diffuse thyroid gland uptake on F-18 FDG PET/CT scans predicts the severity of hypothyroidism.
  
  
  METHODS
  A retrospective analysis of 3868 patients who underwent F-18 FDG PET/CT scans, between October 2012 and June 2013 in our institution for various oncological indications was done. Out of them, 106 (2.7%) patients (79 females, 27 males) presented with bilateral diffuse thyroid gland uptake as an incidental finding. These patients were investigated retrospectively and various parameters such as age, sex, primary cancer site, maximal standardized uptake value (SUVmax), results of thyroid function tests (TFTs) and fine-needle aspiration cytology results were noted. The SUVmax values were correlated with serum thyroid stimulating hormone (S. TSH) levels using Pearson's correlation analysis.
  
  
  METHODS
  Pearson's correlation analysis.
  
  
  RESULTS
  Clinical information and TFT (serum FT3, FT4 and TSH levels) results were available for 31 of the 106 patients (27 females, 4 males; mean age 51.5 years). Twenty-six out of 31 patients (84%) were having abnormal TFTs with abnormal TSH levels in 24/31 patients (mean S. TSH: 22.35 μIU/ml, median: 7.37 μIU/ml, range: 0.074-211 μIU/ml). Among 7 patients with normal TSH levels, 2 patients demonstrated low FT3 and FT4 levels. No significant correlation was found between maximum standardized uptake value and TSH levels (r = 0.115, P > 0.05).
  
  
  CONCLUSIONS
  Incidentally detected diffuse thyroid gland uptake on F-18 FDG PET/CT scan was usually associated with hypothyroidism probably caused by autoimmune thyroiditis. Patients should be investigated promptly irrespective of the intensity of FDG uptake with TFTs to initiate replacement therapy and a USG examination to look for any suspicious nodules.
authors.affiliation: Department of Nuclear Medicine, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India.
authors.forename: Ankur
authors.initials: A
authors.lastname: Pruthi
authors.affiliation: Department of Nuclear Medicine, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India.
authors.forename: Partha Sarathi
authors.initials: PS
authors.lastname: Choudhury
authors.affiliation: Department of Nuclear Medicine, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India.
authors.forename: Manoj
authors.initials: M
authors.lastname: Gupta
authors.affiliation: Department of Nuclear Medicine, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India.
authors.forename: Sameer
authors.initials: S
authors.lastname: Taywade
keywords: Chronic lymphocytic thyroiditis; diffuse thyroid fluorodeoxyglucose uptake; hypothyroidism; maximal standardized uptake value; positron emission tomography; serum thyroid stimulating hormone; thyroid function tests