Endocrine Abstracts

Case: A 10-year-old girl with panhypopituitarism and cerebral palsy secondary to Group B streptococcal meningitis as a neonate had full hormonal replacement therapy (hydrocortisone, thyroxine, DDAVP) since infancy. GH was started at 3 years of age. Sodium levels were always stable in the high normal range. She became epileptic aged seven and was started on sodium valproate. Recurrent chest infections occurred from age eight and she became colonised with Pseudomonas and required home oxygen. In the same year, she stopped feeding orally and became totally gastrostomy fed on a fixed volume of 1000 ml a day. Hydrocortisone was changed to prednisolone at aged seven to facilitate the effects of DDAVP through the day.

GH was stopped at aged nine when it appeared that she was not growing very well. She had been quite ill that year with recurrent chest infections. Her weight escalated despite a calorie reduction in feeds. Prior to stopping GH, her plasma sodium was 138 mmol/l. This fell to 129 mmol/l despite sodium supplements of 3 mmol/kg per day. Urine output was <3 ml/kg per h despite reduction of DDAVP dose. Urinary sodium peaked at 133 mmol/l.

Management: She was admitted for fluid assessment and a cortisol profile whilst hydrocortisone was reintroduced 6 hourly and DDAVP and sodium supplements stopped.

Hyponatraemia and natriuresis persisted till GH was reintroduced at 0.026 mg/kg per day. Urinary sodium fell to <10 mmol/l in the first week of treatment. Urine output was <3 ml/kg per h on no DDAVP. She is still off DDAVP 15 months later.

Conclusions: There are a number of reasons for this complex child to stop DDAVP. Hyponatraemia and reduced urine output implies that there is some endogenous ADH secretion, although vasopressin levels were never confirmed. GH has potent renal tubular antinatriuretic effects. This, coupled with the antidiuretic effect of valproic acid must not be underestimated. Six-hourly dosing of hydorcortisone ensures residual DDAVP works effectively.