This is an exceptionally rare condition. It was first described by Bernhard Reidel in the German literature in 1896.In 30years the authors have only seen 6 true cases. The Mayo Clinic suggests that it is fifty times rarer than Hashimoto's thyroiditis, but we suspect it is even rarer.The patient has a woody hard thyroid (ligneous thyroiditis). Early workers considered it a manifestation of syphilis.
Clinically it is still often thought to be cancer. The French physician Poncet in 1901 suggested that it was a very slow growing form of thyroid cancer, a view now known to be incorrect. The main histological differential diagnosis is the fibrous form of Hashimoto's thyroiditis, which unlike Reidel's thyroiditis is limited to the thyroid. Reidel himself mistook his first case for malignant disease and attempted to resect the thyroid mass and had to abandon the operation owing to the involvement of the adjacent structures. Despite the difficult surgery the patient survived for many years alerting Reidel to the fact that he was dealing with a disease that was not malignant.
The disease does not arise from the thyroid gland and may be associated with fibrosis in other areas such as the orbits, parotid glands and retroperitoneum. When several areas are involved it is called "multifocal fibrosclerositis" or "inflammatory fibrosclerosis".Unlike most thyroid diseases it is only slightly more common in women than men. It may occur in children but more commonly in the adult and elderly patient. The soft tissues of the neck are invaded by fibrous tissue, which strangulates the neck structures, causing swallowing and breathing difficulties. The disease may be asymptomatic or if the fibrous reaction has destroyed the thyroid there may be frank hypothyroidism.
Open biopsy of the thyroid is usually necessary since fine needle biopsy (FNA) is usually inadequate due the woody nature of the thyroid.
Treatment is difficult: steroids may control the progress of the disease but the effect is usually temporary. The breast anti-oestrogen drug Tamoxifen may also be effective. If there is hypothyroidism then thyroxine is indicated. The surgical approach is the same as suggested by Reidel and is limited to freeing the windpipe, splitting the thyroid isthmus to permit the two lobes of the thyroid to fall laterally. Extensive surgery or an attempt at thyroid removal is not necessary and can be horrendously difficult. Despite the invasive nature of the disease, if the windpipe is freed recurrent obstruction is unusual. The surgery is quite odd as the cut fibrous tissue does not bleed. Once the diagnosis is made some localised forms have an excellent prognosis.