RESUMO
BACKGROUND: The variant of Langerhans histiocytosis commonly encountered in adults is the benign, localized form (eosinophilic granuloma). The more-aggressive or diffuse type (Letterer-Siwe disease) is rare in adults. CASE: A 28-year-old woman presented with enlargement of the thyroid gland three years after she had been diagnosed with and placed on treatment for diabetes insipidus. Thyroidectomy was performed following an initial fine needle aspiration cytology report of either papillary thyroid carcinoma or Langerhans cell histiocytosis. The latter diagnosis was confirmed on histopathology and immunohistochemical staining for S-100 protein. Intracellular Birbeck granules were also demonstrated by electron microscopy. The disease progressed over a 10-week period to involve the kidneys, resulting in renal dysfunction. CONCLUSION: Synchronous or metachronous involvement of the hypothalamus and thyroid gland by Langerhans histiocytosis could not be excluded in the present case, with subsequent progression to involve other organs. This was an unusual presentation of the disease in an adult.