A 32-year old male was referred to our clinic because of new onset hypopituitarism and a pituitary stalk lesion suspected for hypophysitis. There was initial transient diabetes insipidus followed by profound hypogonadotropic hypogonadism 6 months prior to diagnosis, and also partial secondary hypothyroidism. Additional diagnostics including extensive laboratory research and a FDG-PET-CT-scan were negative. The working hypothesis was hypophysitis e.c.i. for which radiological follow up was suggested. During further course he developed complete secondary hypothyroidism and new secondary adrenal insufficiency.

Repeat MRI-scan after 1 year showed an increase in volume of the lesion involving the hypothalamus / infundibulum with increased enhancement after contrast, and enlarged optic chiasm, nerves and tracts due to edema. Laboratory tests and lumbar punction again showed no evidence of  systemic disease like granulomatous disorders, vasculitis or IgG4-related disease, or a germinoma or lymphoma. Ophthalmologic examination was normal.

Given the diagnostic uncertainty, growth and involvement of the optic nerves, we decided to perform a transsphenoidal biopsy, which was indicative of Langerhans cell histiocytosis (LCH). A FDG-PET-CT-scan showed increased metabolism at the site of the LCH lesion, but no signs of LCH lesions elsewhere. Thus it is a single system LCH of the central nervous system located in the hypothalamic-pituitary region (HPR). Since LCH is a rare disease, which is even more rare in adults and when isolated to the HPR, only case reports are available and no consensus exists on optimal treatment, ranging from observation to surgery, chemo- and/or radiotherapy. After discussing him in a virtual consultation of ENDO-ERN reference centers we decided to treat him with radiotherapy.

In conclusion, the diagnosis and treatment of LCH limited to the HPR in adults is a considerable challenge given its rarity. It is advisable to discuss these cases in an (international) multidisciplinary consultation to obtain best available knowledge beyond sporadic case reports.