invasive fibrous thyroiditis; Riedel's fibrous thyroiditis; Riedel's struma

Introduction

The rarest form of thyroiditis.

Etiology

unknown

Epidemiology

• woman affected more frequently than men (3:1)
• most frequently occurs in women 30-60 years of age

Pathology

• Morphology:
  • glandular atrophy
  • fibrous replacement of thyroid
  • adhesion to surrounding structures
• May be misconstrued as malignancy.
• Sometimes associated with fibrosis at other sites, especially retroperitoneal or multifocal fibrosis.

Clinical manifestations

• enlargement of a pre-existing goiter
• generally painless
• enlargement of thyroid may cause symptoms
• thyroid hard, woody thyroid mass
• fixation to surrounding structure
• vocal cord paralysis may occur
• associated with other focal sclerosing syndromes (1/3)
  • retroperitoneal
  • cholangitis
  • orbital
  • mediastinal

Laboratory

• T4 generally normal, but may decline with fibrous replacement of thyroid
• biopsy to establish diagnosis & rule-out carcinoma

Management

• no medications of benefit
• surgery is to relieve symptoms of compression

More general terms

• chronic thyroiditis