I have to go to the bathroom!

Ken Cathcart’s case, Steve’s response

Ken: A 61 year old women that had a transphenoidal surgery for Cushing’s disease 15 years presents to establish care. She had post-operative central adrenal insufficiency, hypothyroidism, growth hormone deficiency and ovarian failure. For the last 6 -8 weeks she has noted progressive polyuria, polydipsia, and nocturia. She has no other complaints.

A base line serum sodium was 144 with a normal chloride, glucose and BUN of 20 creatinine of 1.0. A serum osmolality and urine osmolality obtained at the same time as the sodium was 297 serum and urine osmolality of 284. Based on these levels we had the patient fast for 8 hours without oral intake a repeat serum osmolality was now 300 and a serum sodium 144mg/dl. Unfortunately the urine sample was not obtained.

Please note she feels well aside from the thirst

What testing would you do next?
-MRI pituitary
-Formal water deprivation test
-Empiric trial of desmopressin
-Continue to observe the patient

Steve: In Endocrinology a good rule of thumb is to never due imaging before a biochemical diagnosis has been made. That being said, this patient does have a history of pituitary disfunction making this a more mixed picture. I would start with performing a formal water deprivation test, and this is in line with the Endocrine Society’s hypopituitarism guidelines (Fleseriu et al 2016). However with this patient having strong clinical history and already having 4 different deficiencies I think an empiric trial wouldn’t be that unreasonable.

Ken: I agree. I started the patient on 1mg desmopressin tabs daily. Patient called back 2 weeks later, at that time her urination had improved but she had developed leg swelling. I lowered her dose to 1 tab every other day. 1 month later her serum sodium was 138, urine osmolality was 490, and serum osmolality was 280. I believe this confirms the diagnosis of mild central Diabetes Insipidus.

Fleseriu M, Hashim IA, Karavitaki N, Melmed S, Murad MH, Salvatori R, Samuels MH. Hormonal Replacement in Hypopituitarism in Adults: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2016 Nov;101(11):3888-3921. doi: 10.1210/jc.2016-2118. Epub 2016 Oct 13. PMID: 27736313

Photo by Manu Schweneder, unsplash.com

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