Case Summary: A 53-year-old lady who was normally fit and well, presented with a 3 months history of polydipsia and excessive polyuria up to 13 litres a day. A water deprivation test confirmed a cranial diabetes insipidus, and she was started on desmopressin. Apart from hypothyroidism that was well controlled with levothyroxine replacement, the rest of her pituitary profile was unremarkable for a lady of her age. The rest of her investigations showed persistent increased inflammatory markers, a slightly high paraprotein and low IgA. A brain MRI showed empty sella configuration of the pituitary with a normal pituitary stalk and a normal hypothalamus. She later started suffering from headaches, pain around ears, lethargy, joint aches and skin rashes. A CT scan of her temporal bones showed a suspected osteitis in the sphenoid bone, and it was treated with multiple courses of antibiotics. A bone marrow biopsy was done to investigate the high paraprotein and it was unremarkable. A PET scan was organise to look for a cause of the persistent high inflammatory markers. This scan showed multiple avid uptakes in the different long bones, in ribs, in sacral iliac joints and in sphenoid bones. These radiological features were suggestive of Erdheim Chester disease. BRAF V600E mutation identified in the tissue biopsy of her eyelids xanthelasma lesions confirmed the diagnosis. The patient has now been started on methotrexate, but her systemic symptoms have not yet improved. A cardiac MRI did not show any cardiac involvement. Patient is now being followed locally with the input from the national histiocytosis multidisciplinary team.
Conclusion: Erdheim- Chester disease is a very rare histiocytic neoplasm (non-Langerhans cell histiocytosis) with multisystem involvement; its aetiology and pathogenesis have not yet been fully elucidated. It is a disease characterised by multisystem involvement, with the bones being the most affected organ; but other also endocrine systems, cardiovascular and central nervous systems are frequently affected. One of its common endocrine manifestations is diabetes insipidus. The diagnosis of Erdheim- Chester is challenging given its rare prevalence and the non-specificity of its symptoms; this clinical case highlights the importance of widening the scope of investigations when managing unusual clinical presentations.