Hypodipsia, osmoreceptor dysfunction, early puberty and abnormal behaviour in two boys

Abstract

Two unrelated boys (A 13yrs B 18yrs) presenting with early puberty and episodes of aggressive behaviour were found to have hypernatraemia(Na 147-160 mmol/l, osmolality 298-323mosmol/kg) and hypodipsia. Plasma vasopressin(AVP) levels were in the range seen in diabetes insipidus(<2pmol/l), yet 24hr urinary volumes were <1 litre and the maximal urinary osmolality 1232 in A and 950 in B. Plasma renin activity was elevated (>2000mg/AI/l/hr)and aldosterone normal. Excretion of a water load(20ml/kg)was delayed(minimal urinary osmolality A-166 at 300mins,B-392 at 360mins)but plasma renin and aldosterone fell with increased naturesis. An infusion of 4.5% saline produced a rise in AVP(2.8pmol/l)in A but not in B. Insulin and hypotension resulted in release of AVP. (A 6.1pmol/l, B 4.8 pmol/1) suggesting a selective defect of osmoreceptor function. Hyperprolactinaemia and an exaggerated PRL response to TRH were also noted but no intracranial lesion was demonstrable on CT scan. These boys appear to have a hypothalamic syndrome with early puberty, hyperprolactinaemia, hypodipsia and osmoreceptor dysfunction which may be associated with aggressive behaviour.