Serial assessments of anterior pituitary hormones in a case of mixed histiocytosis representing Langerhans cell histiocytosis overlapping with Erdheim–Chester disease

SUMMARY: A 61-year-old man developed central diabetes insipidus caused by mixed histiocytosis (MH) representing Langerhans cell histiocytosis overlapping with Erdheim–Chester disease. Bone, skin, vascular, and retroperitoneal involvements were also observed. Dynamic hormonal testing showed normal responses for anterior pituitary hormones, except for impaired secretion of growth hormone (GH). MRI of the brain showed thickening of the pituitary stalk with slightly reduced signal hyperintensity in the posterior pituitary lobe on T1-weighted imaging. During 2 years of follow-up without radical treatment for MH, imaging studies suggested extension of vascular and retroperitoneal involvements. In contrast, brain MRI did not show any particular interval changes, except for the disappearance of hyperintense signalling in the posterior pituitary lobe. Moreover, no other anterior pituitary dysfunctions beyond GH deficiency emerged during the 2 years of follow-up. The natural history of MH in this case is described, focusing on serial assessments of pituitary functions using dynamic tests. LEARNING POINTS: Erdheim–Chester disease and Langerhans cell histiocytosis overlapping as MH was described, focusing on pituitary functions. MH caused both GH deficiency and central diabetes insipidus. Despite a lack of radical therapy for MH, no other anterior pituitary dysfunctions emerged for 2 years. Radiological images showed no particular interval changes in pituitary stalk lesions, while vascular and retroperitoneal involvements extended.