Malacoplakia of the thyroid gland.

Area of Science:

• Endocrinology
• Pathology
• Microbiology

Background:

• Malacoplakia is a rare acquired disorder characterized by the presence of foamy macrophages (von Hansemann's histiocytes) with characteristic intracytoplasmic and extracytoplasmic inclusions called Michaelis-Gutmann bodies.
• Thyroid malacoplakia is exceptionally rare, with few documented cases, often presenting diagnostic challenges due to its potential to mimic malignant neoplasms.
• Understanding the etiology and pathogenesis of thyroid malacoplakia is crucial for accurate diagnosis and management.

Observation:

• A 50-year-old Japanese woman presented with a thyroid lesion clinically suggestive of malignancy.
• Histologic examination revealed a granulomatous nodule with von Hansemann's histiocytes containing Michaelis-Gutmann bodies, confirming malacoplakia.
• Microscopic examination also identified foci of neoplasm-like or hyperplastic residual thyroid follicles within the lesion.

Findings:

• Electron microscopy demonstrated the presence of bacilliform organisms within the malacoplakic lesion.
• X-ray microanalysis of Michaelis-Gutmann bodies identified phosphorus, calcium, iron, and chloride.
• The findings suggest a potential association between thyroid malacoplakia and coexisting hyperplastic or neoplastic follicular lesions.

Implications:

• The presence of bacterial organisms suggests a role for infection in the pathogenesis of thyroid malacoplakia.
• This case highlights the importance of thorough histologic evaluation for diagnosing rare thyroid conditions that mimic cancer.
• Further research into the interplay between bacterial infection and follicular cell changes in the thyroid is warranted.