Diabetes insipidus for five years preceding the diagnosis of hypothalamic Langerhans cell histiocytosis.

We report a case of an adult male with Langerhans cell histiocytosis (LCH), in which the hypothalamic involvement went undetected by radiology and who was diagnosed as having central diabetes insipidus for 5 years before the skin lesions and the hypothalamic mass became evident on a CT scan. The skin lesions spontaneously disappeared but relapsed 12 months later. The hypothalamic mass disappeared six months after low dose radiotherapy with persistence of diabetes insipidus and loss of thirst sensation. We did not observe relapse of the hypothalamic mass within the five years of post-radiotherapy follow-up. Despite the fact that patients with LCH may experience spontaneous remissions and exacerbations in their clinical manifestations, the patient's long-term evolution suggested the mass was cured. We would like to draw the attention of clinicians to the necessity of long-term follow-up in patients initially diagnosed of idiopathic central diabetes insipidus. Furthermore, low dose radiotherapy is a successful treatment for LCH-dependent masses in the hypothalamus; however, normalization or regression of CT abnormalities after radiotherapy did not affect the clinical diabetes insipidus status.