Case history: PD is a 57-year-old female teacher who presented to her GP in October 2017 with lethargy, dyspnoea and anaemia. Bone marrow biopsy followed by a CT scan of her chest and abdomen confirmed lobular breast cancer with peritoneal and bone metastases (ER+/HER2−). The patient also had an MRI scan of her head to assess for intracranial metastatic disease which was negative at the start of December 2017. She was commenced on letrozole, palbociclib and denosumab. A fortnight after commencing treatment for the breast cancer, the patient was admitted by the GP with intractable thirst symptoms began September 2017 (predated breast cancer diagnosis).
Investigations: Other causes of polyuria were excluded (diuretics; thyroid biochemistry, bone profile, renal profile, anterior pituitary hormone profile, glucose all fine). The patient proceeded to have a water deprivation test in December 2017. The results are shown in Table 1.
Following confirmation of partial cranial diabetes insipidus (DI), reimaging of the posterior pituitary was requested in January 2018 which again demonstrated no intracranial or pituitary pathology.
Results and treatments: The test demonstrates partial cranial DI as there is failure to fully concentrate urine to >750 mosmol/Kg with a serum osmolality >295 mosmol/Kg and improvement of the urine osmolality to 601 mosmol/Kg following administration of DDAVP. The patient was subsequently commenced on regular desmopressin with resolution of symptoms and normal electrolytes.
|Water Deprivation Test|
|Spec No||Time (mins)||Serum Osmolality mosmol/Kg||Urine Osmolality mosmol/Kg|
|2 microgram||DDAVP given|
Conclusions and points for discussion: This is an interesting case of partial cranial diabetes insipidus on a background of metastatic breast cancer without intracranial metastases on radiological surveillance. Serial pituitary MRI scans over 12 months demonstrated no pituitary/intracranial pathology. The patient had good biochemical and symptomatic resolution following treatment. While idiopathic cranial DI is possible, onset of symptoms coincided with development of breast cancer making this less likely.