Diabetes insipidus secondary to TBI

1. What is the cause of diabetes insipidus (DI)?
2. What sort of head fracture typically results in DI?
3. What are the symptoms of DI?
4. What are the findings in the urine and lab values?
5. What is the treatment of neurogenic DI?

Answers:
1. Deficiency of ADH (vasopressin).
2. Fracture near the sella turcica, resulting in tearing of the pituitary stalk. This disrupts ADH secretion from posterior pituitary, resulting in a neurogenic DI.
3. Polyuria, polydipsia. Dehydration is rare unless patient does not drink enough.
4. Urine concentration (<290mm/kg) is usually below serum concentration. Serum shows rising osmolality and rising Na concentration.
5. Desmopressin is an ADH analog that can be given intranasally or intramuscularly. Chlorpropamid potentiates effects of ADH on renal tubules and can be used in partial ADH deficiency.