Riedel Thyroiditis

Riedel thyroiditis is a rare invasive fibrosing disease of the thyroid, part of IgG4 related disease in many.

• Women aged 30 to 60; fibrosis extends to neck structures.
• Associated with multifocal fibrosclerosis (retroperitoneal fibrosis, sclerosing cholangitis, orbital pseudotumour, mediastinal fibrosis).
• Hypothyroidism develops in 30 to 40%; hypoparathyroidism in some.

• Painless, stony hard, fixed goitre, often asymmetric.
• Dyspnoea, stridor, dysphagia, hoarseness, pressure sensation.
• Symptoms of hypothyroidism or hypoparathyroidism.
• Features of extra thyroidal fibrosis.

• TSH, free T4, TPO antibodies (positive in 60%), calcium and PTH, ESR/CRP, serum IgG4.
• Ultrasound: hypoechoic, hypovascular gland.
• CT/MRI: invasion of adjacent tissue.
• Open biopsy is the gold standard (fine needle aspiration is non diagnostic): dense fibrosis extending beyond the capsule with lymphoplasmacytic infiltrate, obliterative phlebitis; exclude anaplastic carcinoma and lymphoma.

• Glucocorticoids first line: prednisolone 40 to 60 mg daily for 1 to 2 months, taper over 6 to 12 months.
• Steroid sparing or refractory: tamoxifen 10 to 20 mg twice daily, rituximab 1 g on days 1 and 15, mycophenolate, methotrexate.
• Surgery (isthmusectomy/decompression) for airway compromise; avoid extensive resection (high risk).
• Levothyroxine and calcium/vitamin D replacement as needed.
• Screen for other fibrotic disease. Prognosis is good with treatment.