This is an extremely rare sclerosing disease of unknown aetiology. It is characterised by replacement of the thyroid parenchyma with dense fibrous tissue which extends beyond the thyroid capsule into surrounding structures in the neck. Peak incidence is in the fourth to seventh decade with a female predominance of 3:1.
Usually, the main complaint is of a painless lump in the neck. Rarely, there may be dysphagia, dyspnoea, stridor, or suffocation. Hypothyroidism occurs in 25-50% of cases. The thyroid is woody or iron-hard. It is usually markedly contracted and difficult to palpate. Rarely, it may be of normal size or slightly enlarged. Occasionally there may be features of compression.
The condition may resemble an infiltrating carcinoma and may be associated with other idiopathic fibrosing conditions such as sclerosing cholangitis and fibrous mediastinitis.
Surgery may be needed to relieve pressure on the trachea. It is uncommon for thyroidectomy to be required.