A Case of Burnt-Out Langerhans Cell Histiocytosis Presenting as Postpartum Hypopituitarism

OBJECTIVE: To evaluate the case of a woman who presented with central hypogonadism and diabetes insipidus and further developed a persistent cough leading to an unexpected diagnosis of burnt-out Langerhans cell histiocytosis (LCH). METHODS: Clinical and laboratory endocrine evaluation, magnetic resonance imaging, high-resolution computed tomography, and open-lung biopsy results are discussed. RESULTS: A 28-year-old woman presented at 10 months postpartum with polydipsia, polyuria, and amenorrhea for 3 months. Her results showed a prolactin level of 25 μg/L (reference,<23.5 μg/L), estrogen level of 91 pmol/L (reference, 110-180 pmol/L), follicle-stimulating hormone level of 6 IU/L (reference, 2-20 IU/L), and luteinizing hormone level of 6 IU/L (reference, 2-70 IU/L). A water-deprivation test found a sodium concentration of 148 mmol/L (reference, 135-145 mmol/L), serum osmolality of 310 mmol/kg (reference, 275-295 mmol/kg), and urine osmolality of 107 mmol/kg (reference, 50-1450 mmol/kg) that improved to 142 mEq/L, 295 mmol/kg, and 535 mmol/kg, respectively, after desmopressin administration. Gadolinium-enhanced pituitary magnetic resonance imaging demonstrated a markedly thickened stalk with uniform enhancement. Chest high-resolution computed tomography confirmed bilateral upper-zone cystic lung disease suggestive of either pulmonary lymphangioleiomyomatosis or LCH. Eventual histology showed CD1a-positive burnt-out LCH. This differentiation was crucial as pulmonary lymphangioleiomyomatosis exacerbates with estrogen therapy and pregnancy, which the patient was able to successfully pursue without disease exacerbation. CONCLUSION: The patient’s initial presentation was considered as lymphocytic hypophysitis, but subsequent cystic changes on high-resolution computed tomography led to a unifying definitive diagnosis of burnt-out LCH. This case highlights the importance of investigating for uncommon secondary causes of hypophysitis.