maintenance of a normal serum sodium concentration is dependent on both an intact thirst sensation and the action of arginine vasopressin ( avp ) , also known as antidiuretic hormone .
thirst osmoreceptors and cell bodies containing avp overlap in location in the hypothalamus and share a common blood supply through branches of the anterior communicating artery 1 . thus , disruption of this blood supply can result in both lack of thirst and avp synthesis , in response to appropriate stimuli of hypernatremia and hyperosmolality .
herein , we report the case of adipsic diabetes insipidus following anterior communicating artery clipping . at presentation , the patient had no perception of thirst despite the presence of significant hypernatremia .
the fluid management in this case is rendered more complex due to the patient having poor shortterm memory and the subtropical climate in queensland , australia .
a 36yearold woman was transferred to our hospital for further investigation and management of a subarachnoid hemorrhage ( sah ) .
she had initially presented to the emergency department following a syncopal episode on a background of a 2day history of a severe frontal headache associated with nausea and vomiting .
physical examination at the time of admission revealed weight of 85 kg , heart rate 84/min , blood pressure 140/85 , respiratory rate 16 breaths / min , and oxygen saturation 99% on room air .
computerized tomographic angiography ( cta ) revealed a ruptured 5 mm anterior communicating artery aneurysm ( fig .
endocrinology was notified for review after her urine output was recorded at 7.5 l on the day of the procedure .
aneurysm arising from the anterior communicating artery and proximal a2 segment of the right anterior cerebral artery  ( a )
preoperative serum sodium concentration on the morning of surgery was normal at 136 mmol / l ( reference range : 135145 ) .
the following morning , the serum sodium level was 153 mmol / l and serum osmolality was 318 mosmol / kg ( reference range : 280295 ) . serum sodium concentration had further increased to 156 mmol / l 2 h later . the urine was dilute , with hourly urine output elevated at 300400 ml / h . a clinical diagnosis of central diabetes insipidus was made . despite the clinical presence of volume depletion and significant hypernatremia , the patient had no perception of thirst .
given the anatomy and location of the aneurysm , the most likely diagnosis was adipsic diabetes insipidus secondary to clipping of the anterior communicating artery aneurysm .
values varied from 159 to 823 mosmol / kg , depending on the temporal relationship with the administered desmopressin .
there was no evidence of major temperature dysregulation  in the immediate postoperative period , temperature varied between 36.5 and 38.1c , and by the second postoperative week was consistently between 36 and 37c .
nmol / l at 08:10 h , free thyroxine concentration 7.2 pmol / l ( reference range : 717 ) , thyroidstimulating hormone ( tsh ) concentration 0.9 mu / l ( reference range : 0.34.5 ) , prolactin 374 mu / l ( reference range : 71566 ) , estradiol 141 pmol / l , folliclestimulating hormone ( fsh ) 1.8 u / l ( reference range : 18 ) , and luteinizing hormone ( lh ) 0.6 u / l ( reference range : 112 ) . during the acute period , the patient was initially monitored with hourly urine output , twice daily electrolytes , and daily weighs .
initial parameters for repeat desmopressin administration were the presence of breakthrough polyuria , defined as a urine output of > 350 ml / h for two consecutive hours , or > 300 ml / h for three consecutive hours .
several doses of parenteral desmopressin were required over the following 72 h. treatment was then commenced with regular oral desmopressin 100 g in the morning and 200 g in the evening .
the patient continued to have no perception of thirst . based on her fluid balance chart after commencing oral desmopressin ,
therefore , she was placed on a regular water prescription of 250 ml eight times a day .
it was not deemed necessary to perform a formal water deprivation test or infusion of hypertonic saline to confirm the diagnosis in this clinical setting .
she was then transferred to the brain injuries unit for rehabilitation of shortterm memory impairment .
after initiation of regular oral desmopressin and a fixed dose water prescription , the patient was able to maintain a normal serum sodium concentration in hospital .
serum sodium concentration was initially monitored on a daily basis , with the interval being extended to twice weekly prior to discharge .
discharge planning involved ongoing followup with weekly bloods for serum sodium concentration with her general practitioner .
the desmopressin was increased to 200 g twice daily and the water prescription also modified , aiming for approximately 1 l above urine output .
it was thought that insensible losses in the queensland late spring / summer accounted for the increased fluid requirements , as 24h urine volumes were not excessive and there was no nocturia .
further review 2 months later revealed some improvement in cognitive function and stable normal electrolytes ( serum na 139142 mmol / l ) on the above regimen .
longitudinal followup out to 15 months post sah has been undertaken . while improved , significant shortterm memory impairment persists .
repeat assessment at 1 year indicates that her anterior pituitary function remains intact and she has regular menses .
mmol / l since she has been living with family support in her own home .
the most commonly reported causes include congenital lesions such as septooptic dysplasia , germinoma , anterior communicating artery rupture or clipping , and craniopharyngioma 2 .
crowley et al . 3 have reported a series of 13 patients , of whom four were the result of anterior communicating artery aneurysm surgery . a case report and review of
the literature published in 2008 revealed 10 cases of adipsic diabetes insipidus following clipping of an anterior communicating artery aneurysm 2 .
two subsequent case reports have since been identified 4 , 5 . even in the presence of hypernatremia
published cases have continued management in the community by using a combination of regular desmopressin and a fixed dose water prescription 6 , 7 .
calculating an ideal body weight when the patient is euvolemic provides a set point from which water intake can be adjusted .
a behavioral modification technique for the patient with shortterm memory impairment has also been described with the use of a wristwatch alarm 8 .
this report demonstrated the success of a staged technique , first by regular prompting by staff and initiation of a reward system when all water was consumed in a day .
the rewards were gradually withdrawn and the patient maintained a stable serum osmolality by the use of a wristwatch alarm as the prompt to drink .
the present case had isolated diabetes insipidus in the presence of normal anterior pituitary function .
once the immediate postoperative period had passed , a regular twice daily dose of oral desmopressin coupled with a prescribed fluid intake resulted in stable serum sodium concentrations while in the rehabilitation ward .
the challenge was to maintain this level of stability when she is living in the community .
this is particularly important given the patient 's subtropical geographical location of southeast queensland , australia where there are high ambient temperatures and humidity during the summer months ( latitude 27 south , mean maximum ambient temperature 2829c , humidity 6570% ) , which will increase insensible fluid losses .
this required adjustment in her water prescription , over and above what would generally be required in a temperate climate .
this is in part related to associated conditions of nonendocrine hypothalamic dysfunction , such as obesity , temperature dysregulation , and sleep disorders , but also an apparent increased rate of venous thromboembolism 3 and serious infections 9 . when compared to patients with diabetes insipidus and normal thirst perception , patients with
adipsic diabetes insipidus are more than 10 times more likely to develop significant outpatient hypernatremia ( > 150 mmol / l ) 10 .
close monitoring in conjunction with the patient 's general practitioner is an essential component of the longterm management .
this has resulted in acceptable stability in the patient 's serum sodium despite the triple challenge of adipsia , poor shortterm memory and humid subtropical climate .
 key clinical messagediabetes insipidus without perception of thirst , as may follow an anterior communicating artery aneurysm , requires prescription of fluid intake as well as desmopressin . 
 the management goal of maintaining a normal serum sodium is rendered more challenging in a humid subtropical environment , where insensible losses are higher . 