Review Question - QID 221275

This patient who presents with hypothyroidism as well as a symmetrically enlarged, hard, and nontender thyroid most likely has Riedel thyroiditis.

Riedel thyroiditis, also known as invasive fibrous thyroiditis, is a rare condition characterized by the infiltration of IgG4-secreting plasma cells beyond the thyroid into the perithyroidal soft tissue with associated fibrosis. Due to the invasion of perithyroidal tissues, patients can present with hypoparathyroidism, hoarseness, and dyspnea. Patients often present with a slowly growing, painless goiter that is nontender and “rock” hard. It is densely adherent to the adjacent tissues and therefore moves poorly with swallowing. A third of patients will have hypothyroidism due to nonfunctioning fibrous infiltration. If left untreated, the condition may slowly progress to stabilization or even regress spontaneously. Therapy may be indicated if there is progressive perithyroidal infiltration or potentially life-threatening destruction of local structures. Treatments may include glucocorticoids, tamoxifen, and surgical removal.

Falhammar et al. studied the clinical presentation, treatment, and outcomes in a cohort of 6 patients. They found that 5 of 6 patients presented with hypothyroidism and 4 had extrathyroidal manifestations. They recommend that glucocorticoids should be used as first-line treatment, but other medications should be considered to reduce the risk of fibrosclerosis in the thyroid and other organs.

Figure/Illustration A is a histological slide demonstrating fibrosis and infiltration of lymphocytes (red circle) in the thyroid gland. This appearance is consistent with a diagnosis of Reidel thyroiditis.

Incorrect Answers:
Answer 1: Anaplastic thyroid cancer presents with a rapidly growing neck mass with invasion of surrounding structures. As Riedel thyroiditis also infiltrates surrounding structures, the physical examination may raise suspicion for invasive thyroid cancer. Patients with anaplastic thyroid cancers are usually over the age of 65 and have normal TSH levels. Histology would show invasion of undifferentiated cells into the thyroid gland.

Answer 2: Hashimoto thyroiditis is an autoimmune disease characterized by a painless goiter. Patients present with symptoms of hypothyroidism such as weight gain, fatigue, or constipation. This disease presents with antithyroid peroxidase and antithyroglobulin antibodies. Although Riedel thyroiditis is associated with Hashimoto thyroiditis, this patient’s hard thyroid with signs of infiltration is more suggestive of Riedel thyroiditis.

Answer 4: Subacute thyroiditis (de Quervain) is a post-viral inflammation of the thyroid gland. The disease is self-limited and rarely progresses. Patients often present with a tender thyroid, fevers, malaise, and elevated erythrocyte sedimentation rate (ESR). Labs typically show elevated T3 and T4 and low TSH due to negative feedback.

Answer 5: Thyroid adenoma is a benign tumor of the thyroid gland, which usually presents as a nonfunctional thyroid nodule. It rarely presents with a diffusely enlarged thyroid that is hard. In addition, some nodules may be functional and result in hyperthyroidism but rarely hypothyroidism (low free T4 and high TSH).

Bullet Summary:
Riedel thyroiditis is characterized by a hard, nontender, diffusely enlarged thyroid.