Background This six year old girl unusually has central diabetes insipidus without polydipsia; with accompanying growth hormone deficiency and hyperprolactinaemia. She presented with 2 years of worsening breathlessness on minimal exertion, weight gain, poor linear growth and marked sweating in all weathers. Initial assessment revealed short stature (Height SDS-3.0), obesity (BMI 98th centile) and mild dehydration.
Methods Investigations demonstrated hypernatraemia (sodium 168 mmol/L), hyperprolactinaemia (prolactin 3341 miu/L), normal thyroid function and low Insulin-like growth factor-1. MRI pituitary demonstrated no microprolactinoma or other CNS lesion. Extremely low peak GH 0.5 ug/L (normal >7 ug/L) on Insulin tolerance testing indicated growth hormone (GH) deficiency, but normal cortisols. Inpatient assessment demonstrated absence of thirst despite persisting hypernatraemia, high serum osmolality (356mOsmol/kg), inappropriately dilute urine (79mOsmol/kg) and urine output 4ml/kg/hour. Low serum vasopressin 1.4 pmol/L. Negative tumour markers.
Results GH replacement was extremely effective with improvement in height and normalisation of BMI. Managing her adipsic DI was challenging. Increasing oral intake of 1800 ml/day was insufficient. DDAVP IM achieved urinary concentration (779mOsmol/kg), but Oral DDAVP was ineffective, despite high daily dose 1000 ug. Normalisation of serum sodium and urine output was finally achieved with nasal DDAVP, although slight hyperosmolality persists. The patient has continued to experience excessive sweating. Serial MRIs continue to be normal.
Conclusion This unusual case of adipsic diabetes insipidus with excessive sweating is likely to represent hypothalamic dysfunction although no structural lesion is identified on MRI brain. Case series of adipsic diabetes insipidus have identified a high frequency of hypothalamic abnormalities associated with significant morbidity and mortality.