Insipidus

A Case of Diabetes Insipidus

by

David F. Dean

Department of Biology

Spring Hill College

Case Presentation

Amanda Richards is a -year-old junior in college. She is majoring in biology

and hopes someday to be a pediatrician. Beginning about a month ago, Amanda

noticed that she was waking up once, sometimes twice a night, by the need to

go to the bathroom. More recently, she has noticed that she needs to go to the

bathroom during her school day much more frequently than before, sometimes

as often as once every hour.

At first Amanda thought that her increased frequency of urination was due to

the coffee she drank, but when she reduced her coffee consumption to one cup

in the morning, she still needed to go to the bathroom just as often. In addition,

Amanda was buying bottled water by the case, and she found herself never

without a beverage in her hand or nearby. She also noticed that her urine seemed

pale and colorless.

When Amanda told her mother of her problem, her mother became very

concerned and arranged for Amanda to see the family physician. Her physician

found no abnormalities on physical examination. However, a blood chemistry

profile revealed Amanda’s plasma sodium level to be  mEq/L, plasma

osmolarity was  mOsm/L, and her fasting plasma glucose was  mg/dl. An

analysis of Amanda’s urine showed a urine osmolarity of  mOsm/L. The urine

sample was negative for the presence of glucose.

An extensive history revealed that no other member of the family had ever

displayed Amanda’s symptoms. Amanda had no history of traumatic head injury

and an mri of her brain was normal.

Next, a two-hour water deprivation test was performed on Amanda. After two

hours of not being able to drink water, the osmolarity of her plasma and urine

were measured a second time. This time her urine osmolarity was unchanged;

however, the osmolarity of her plasma increased to  mOsm/L. She was then

injected with a drug called ddavp. One hour after the...