Thyroiditis and mimickers

Abstract

Acute suppurative thyroiditis The thyroid gland is resistant to infection, because of its encapsulation, high iodide content, rich blood supply, and extensive lymphatic drainage, therefore suppurative thyroiditis is rare. It is a potentially life-threatening endocrine emergency, most likely to occur in patients with preexisting thyroid disease. The most common etiology is bacterial infection, except in immunocompromized patients. With effective antibiotic therapy and elimination of formed abscesses by ultrasound-guided FNA, patients typically have an excellent prognosis if they survive the acute episode. The author encountered one case in 1993. FNA of acute suppurative thyroiditis is characterized by fibrinopurulent exudate containing numerous neutrophils, just like the aspirates from any other sites. Riedel's thyroiditis Riedel's thyroiditis is a progressive fibrosis of the thyroid gland that may extend to surrounding tissues of unknown etiology. Patients with Riedel's thyroiditis present with a rock-hard, fixed, painless thyroid nodule. FNA of Riedel's thyroiditis would be non-diagnostic, since no colloid or follicular cells would be aspirated. However, the acellular yield would support the clinical impression of Riedel's thyroiditis. Subacute /De Quervain's thyroiditis Subacute thyroiditis, also known as subacute granulomatous thyroiditis, is a self-limited thyroid condition associated with a triphasic clinical course of hyperthyroid, hypothyroid, and euthyroid. Laboratory tests early in the course of the disease may show low serum TSH (thyroid-stimulating hormone) level, high serum free T4 (thyroxine) level, low radioactive iodine uptake, and high erythrocyte sedimentation rate. The high T4 level results from release of pre-formed thyroid hormone into the circulation from the ruptured thyroid follicles. Laboratory tests later in the disease may show high serum TSH level and low serum free T4. Subacute thyroiditis may be responsible for 15–20% of patients presenting with thyrotoxicosis and 10% of patients presenting with hypothyroidism. Recognizing this condition is important, because it is self-limiting, and there is no specific therapy.