Endocrine Abstracts

History: 80 years old male was admitted in June 2016 with a head injury. His CT head showed small subarachnoid haemorrhage and shallow frontal subdural hematoma. He was managed conservatively as per advice from neurosurgical department and was discharged on 4^th July. He was readmitted on 9^th July suffering from confusion and found to have sodium of 114 which was 141 a week ago.

Investigation: Investigations carried out to find the cause of low Na showed serum osmolality of 232, urine osmolality of 479, urinary Na of 60 with normal cortisol and thyroid function test.

Management: He was put on fluid restriction to 750 mls, followed by sodium tablets but despite that Na remained low with range 109–116. During admission he had further falls and repeat CT head showed stable appearance of previous finding. Apart from confusion he never developed any other symptom of neurological deficit. Due to poor response to standard treatment and being symptomatic he was given one stat dose of 5 mg of Tolvaptan on 28^th July which improved Na gradually to 125 by 2^nd Aug with clinical improvement so he was discharged home with the advice to continue fluid restriction. During that admission his medications were reviewed as well. Unfortunately his Na levels subsequently dropped leading to re- admission with confusion on 10^th Aug with Na of 118 which further dropped to 112 and again he failed to respond to strict fluid restriction when Tolvaptan dose (5 mg) was repeated on 18^th Aug and caused safe improvement in Na to 119 on 19^th Aug and to 123 by 23th Aug which was maintained with clinical improvement in symptoms. He was monitored in endocrine clinic thereafter, his Na levels oscillated with normal results in Oct 16 then reducing to 127 in Dec 16 and finally returning to normal in Jan 17.

Conclusion: This is an example of hyponatremia due to SIADH secondary to traumatic brain injury with recurrent episodes of hyponatremia, resistant to fluid restriction and sodium tablets. It is important to identify such patients and exclude other differentials like cerebral salt wasting. This case illustrates safe and effective use of Tolvapatan as a single small dose in the treatment of SIADH which can be done at the general ward level. It is interesting to see that sodium levels recovered and maintained after single dose Establishing the dose of Tolvaptan needs further discussion and experience.