1. Acute bacterial (suppurative) thyroiditis is rare. Infection spreads by the hematogenous route or by continuity from adjacent tissues.
Etiology: Streptococci (Streptococcus pyogenes), staphylococci (Staphylococcus aureus), less frequently Escherichia coli and Salmonella typhimurium; in recurrent infections, anaerobic bacteria. The disease initially manifests as a painful swelling of the thyroid gland with fever and rigors. Formation of an abscess is accompanied by painful regional lymphadenopathy. Thyroid function is usually normal.
Ultrasonography shows decreased heterogeneous echogenicity of the abscess. On radionuclide imaging the abscess is “cold” and shows no radionuclide uptake. Cytology shows only purulent contents (send a sample for culture and antibiotic susceptibility). White blood cell counts are high and erythrocyte sedimentation rate is markedly elevated.
The treatment of choice is inpatient antibiotic therapy and surgical drainage of the abscess or a total or partial surgical resection of the affected thyroid gland. Immediately after collecting samples for microbiology start empiric antibiotic therapy based on risk factors, severity of infection, previous history of allergic reactions to antibiotics, and recently used antimicrobial treatment.
2. Radiation-induced thyroiditis develops after radioiodine treatment. Following the acute inflammatory phase, patients can develop hypothyroidism. The disease may also occur after external beam irradiation used in oncology; in such cases it appears late, has no acute phase, and is termed “radiation-induced hypothyroidism.”
3. Thyroiditis caused by trauma (including vigorous palpation) of the thyroid gland.
4. Drug-induced thyroiditis: Some drugs, such as, lithium, interferon alpha, interleukin 2, amiodarone, and tyrosine kinase inhibitors, may cause symptoms of acute thyroiditis. Amiodarone-induced thyroiditis: see Other Types of Chronic Thyroiditis.