BACKGROUND: Invasive fibrous thyroiditis (IFT) is the rarest form of 
thyroiditis, and reports are often limited to case reports and small case 
series. In this study, we aimed to summarize our institutional experience with 
IFT since 1976.
METHODS: We retrospectively reviewed the cases of all patients with IFT 
evaluated at Mayo Clinic, Rochester, Minnesota, from 1976 through 2008, with 
special emphasis on clinical presentation, associated risk factors, associated 
comorbid conditions, complications, and treatment.
RESULTS: Twenty-one patients met our inclusion criteria of (i) IFT confirmed by 
pathologic review at our institution and (ii) evidence of extension of fibrosis 
outside the thyroid capsule. Most patients (17, 81%) were women (mean age, 42 
years). Presenting symptoms included pain (24%), dysphagia (33%), vocal cord 
paralysis (29%), and tracheal narrowing (48%). Three patients had associated 
hypoparathyroidism. Sixteen (76%) had a history of tobacco use, and 10 (48%) 
were current smokers. Fibrosing mediastinitis was present in four, orbital 
fibrosis in one, retroperitoneal fibrosis in three, and pancreatic fibrosis in 
one (38% had extracervical fibrotic processes). Eighteen patients had partial 
thyroidectomy, 7 (39%) of whom had surgical complications involving vocal cords 
and parathyroid. Two required tracheostomy. Thirteen had corticosteroid therapy; 
six received tamoxifen. There was no cause-specific mortality, and the fibrotic 
process stabilized or partially resolved in all patients.
CONCLUSIONS: IFT often is associated with a systemic extracervical fibrotic 
process and tobacco use. Attempted thyroid resection often results in 
postoperative complications. Long-term follow-up showed no deaths from IFT and 
showed stability of the thyroiditis.