Diabetes Insipidus Case Study
Libby was in her third week in the hospital after her car accident and was getting anxious to go home. She'd fractured her skull and broken both of her legs. She felt lucky to be alive, but not so lucky to be spending another day watching bad TV and eating bland hospital food. So, when the doctor came in to check on her she asked her "so, when am I getting out of here?" The doctor gave a sympathetic smile but had some bad news:
"Well, we're a little concerned about one thing: your nurse told us that you produced 6 liters of urine yesterday. That's a lot more than usual. And I guess you've probably been drinking a lot, too?"
"Yeah," said Libby. "I have been feeling really thirsty, now that you mention it."
"Well, we're concerned that you might have something called diabetes insipidus related to your head trauma."
"Diabetes from head trauma?" Libby was confused and worried. "Do I have to take insulin?"
"Diabetes insipidus is totally different from diabetes mellitus, which has to do with your blood sugar and insulin. The only reason why they're both called 'diabetes' is because they both make you pee a lot. We're going to do something called a fluid deprivation test to see if you have diabetes insipidus or not. That means that you can't drink any more water, and unfortunately, you're going to be here for a couple more days. Sorry!"
Use the information from this sheet and any other reliable resources available to you to answer the following questions.
1. What is diabetes insipidus?
2. How could head trauma cause diabetes insipidus?
3. Describe the detailed mechanism by which the hormonal changes associated with diabetes insipidus would trigger increased thirst.
4. How is diabetes insipidus usually treated? What complications may arise from unchecked diabetes insipidus?
5. In a fluid deprivation test, water is withheld from the patient and the osmolarity of urine is checked. How would urine osmolarity change in a healthy person in response to fluid deprivation? How would it change in someone with diabetes insipidus due to head trauma?
1. Diabetes insipidus (DI) is a condition that is defined by excretion of an unusually large volume of urine (more than 3 liters in a day) or urine that is very diluted (<300 mOsm/kg body weight). This can be caused by either decreased production of antidiuretic hormone (ADH) by hypothalamus (via posterior pituitary gland) (central DI) or kidney's resistance to ADH (nephrogenic DI). Think about it the same way you would for diabetes mellitus, which can also be caused by either lack of insulin production by islets of Langehans cells in pancreas or body resistance to insulin.
2. Head trauma can result in DI since ...
We discuss of case of central (neurogenic) diabetes insipidus caused by a traumatic brain injury, along with pathophysiology, treatment and a confirmatory test.