Acute Suppurative / Infectious Thyroiditis

• Introduction:
  • Infectious thyroiditis is also known as:
    • Acute thyroiditis
    • Suppurative thyroiditis
    • Bacterial thyroiditis
    • Pyogenic thyroiditis
  • Bacterial infections of the thyroid are extremely rare:
    • With only:
      • 224 cases having been reported in the literature from 1900 to 1980 (adult literature)
      • 60 cases reported in the pediatric literature
    • Bacterial infections:
      • Are the most common causes of infectious thyroiditis
      • The infections are generally:
        • Suppurative and acute
  • Infectious thyroiditis caused by:
    • Fungal and parasitic infections:
      • Are more frequently chronic and indolent

• Etiology and Pathogenesis:
  • The thyroid gland’s high iodine content, significant vascularity, lymphatic drainage as well as its protective capsule:
    • Provide the thyroid gland with notable resistance to infection
  • The most common predisposing factor to infections of the thyroid appears to be:
    • Preexisting thyroid disease has been observed in up to two thirds of women and one half of men with infectious thyroiditis:
      • Simple goiter
      • Nodular goiter
      • Hashimoto’s thyroiditis
      • Thyroid carcinoma
    • Patients with the acquired immunodeficiency syndrome (AIDS):
      • Are a population particularly at risk for bacterial thyroiditis:
        • As with other opportunistic infections in AIDS patients, infections of the thyroid gland often are chronic and insidious in onset
  • In the adult:
    • Staphylococcus aureus and Streptococcus pyogenes are the offending pathogens:
      • In more than approximately 80% of patients:
        • And are the sole pathogen in over 70% of cases
  • In children:
    • Alpha- and beta-hemolytic Streptococcus and a variety of anaerobes:
      • Account for approximately 70% of cases:
        • Whereas mixed pathogens are identified in greater than 50% of cases
  • Other thyroidal bacterial pathogens that have been shown to cause infectious thyroiditis include:
    • Salmonella brandenburg
    • Salmonella enteritidis
    • Actinomyces naeslundi
    • Actinobacillus actinomycetemcomitans
    • Brucella melitensis
    • Clostridium septicum
    • Eikenella corrodens
    • Enterobacter
    • Escherichia coli
    • Haemophilus influenzae
    • Klebsiella sp.
    • Pseudomonas aeruginosa
    • Serratia marcescens
    • Acinetobacter baumannii
    • Staphylococcus nonaureus
  • Pathogenesis of Acute Suppurative Thyroiditis:
    • Bacterial:
      • 68% of the cases
    • Parasitic:
      • 15% of the cases
    • Mycobacterial:
      • 9% of the cases
    • Fungal:
      • 5% of the cases
    • Syphilitic:
      • 3% of the cases
  • Infection and suppuration may result from:
    • Direct spread from a nearby infection
    • Via the bloodstream
    • Via the lymphatics
  • The seminal observation regarding the pathogenesis of bacterial thyroiditis was made in 1979 when Takai et al.:
    • Who reported seven cases of infectious thyroiditis:
      • Caused by a fistula originating from the left pyriform sinus
    • Subsequently, studies involving more than 100 patients with infectious thyroiditis:
      • Have identified pyriform sinus fistulae:
        • Primarily left-sided, in up to 90% of these patients, especially in those with recurrent episodes
  • Additional reports identified as routes of thyroidal infection:
    • Infected embryonic cysts from the third and fourth brachial pouches
    • Thyroglossal duct cysts  
  • On pathologic exam:
    • The characteristic changes of acute bacterial inflammation, including :
      • Necrosis and abscess formation:
        • Are commonly found

• Clinical Manifestations:
  • Bacterial thyroiditis is often preceded by an upper respiratory infection:
    • Which may induce inflammation of the fistula and promote the transmission of pathogens to the thyroid.
  • Consistent with these observations:
    • Bacterial thyroiditis is more common:
      • In the late fall and late spring months
  • Over 90% of patients will present with:
    • Thyroidal pain:
      • The pain is often referred diffusely to adjacent structures
    • Tenderness
    • Fever
    • Local compression resulting in dysphagia and dysphonia
    • Systemic symptoms are frequently seen, such as:
      • Fever
      • Chills
      • Tachycardia
      • Malaise
• Laboratory Findings:
  • Thyroid function tests are usually normal:
    • However:
      • Cases of hypothyroidism and thyrotoxicosis have been reported
  • The polymorphonuclear leukocyte count and the sedimentation rate:
    • Are usually elevated
  • The organism frequently can be identified by:
    • Gram stain and culture of a fine-needle aspiration in the region of suppuration:
      • Although sterile cultures are seen in approximately 8% of cases
• Imaging:
  • A nuclear medicine thyroid scan:
    • May show the suppurative region as a “cold” area
  • Ultrasound examination may reveal:
    • A cystic or “complex” nodule

• Diagnosis:
  • The diagnosis is made with:
    • A fine-needle aspiration
    • Gram stain
    • Culture
  • Symptomatically:
    • Infective thyroiditis may be difficult to differentiate from subacute thyroiditis in the early phases:
      • Although the characteristic thyroid function changes in the latter disease should be helpful in discriminating the two
  • Leukocytosis and an elevated erythrocyte sedimentation rate are not discriminatory tests:
    • As they are commonly observed in both subacute thyroiditis and infectious thyroiditis
  • In general:
    • Patients with bacterial thyroiditis have a greater febrile response than those with subacute thyroiditis
  • Once abscess formation has occurred:
    • The local redness, lymphadenopathy, hyperpyrexia, and leukocytosis should lead to the correct diagnosis
  • Malignant neoplasms and hemorrhages into cysts:
    • May sometimes present with manifestations that mimic this disorder
• Clinical Management:
  • The prognosis of bacterial thyroiditis:
    • Is often dependent on the prompt recognition and treatment of this disorder:
      • As mortality may approach 100%:
        • If the diagnosis is delayed and appropriate antimicrobial therapy is not instituted
    • Much depends on the identification of the microorganism:
      • From the needle aspirate, incision, and drainage, or occasionally from blood culture
      • If no organisms are seen on the Gram stain:
        • Nafcillin and gentamicin or a third-generation cephalosporin is the appropriate initial therapy in adults
        • A second-generation cephalosporin or clindamycin is reasonable in children
      • If an abscess develops and prompt response to antibiotics does not occur:
        • Incision and drainage are necessary:
          • Sometimes partial lobectomy must be performed,:
            • Especially if the disease is recurrent
      • Usually the lesions heal with reasonable speed after initiation of the correct antimicrobial agent, and recurrences are uncommon.
      • Mortality from acute bacterial thyroiditis has markedly improved from the 20% to 25% reported in the early 1900s:
        • With the extensive review by Berger estimating an overall mortality of 8.6%
        • In one review of more than 100 patients, mortality as a complication of acute bacterial thyroiditis was not listed

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