Question 4 A 54-year-old man with a medical history significant for bipolar disease presents to his physician with complaints of polyuria. He states that he must get up three or four times each night...

Question 4

A 54-year-old man with a medical history significant for bipolar disease presents to his physician with complaints of polyuria. He states that he must get up three or four times each night to urinate. He also notes frequent thirst. He denies polyphagia, urinary urgency, difficulty initiating urination, and postvoid dribbling. His medical history is notable only for bipolar disease. He has a long-standing history of noncompliance with medications for this disease, with frequent hospitalizations for both mania and depression, but has been stable on lithium for the past 6 months. He denies any symptoms of mania or depression at this time. He takes no other medications. Family history is notable for depression and

substance abuse but is otherwise negative. The patient has a history of polysubstance abuse but has been “clean and sober” for the past 6 months. On examination, the patient’s vital signs are within normal limits. Head-neck examination reveals slightly dry mucous membranes. Rectal examination reveals a normal prostate without masses. The remainder of his examination is unremarkable. Urinalysis reveals dilute urine without glucose or other abnormality. Serum electrolytes reveal a mildly increased sodium level. A diagnosis of diabetes insipidus is entertained.

Questions

1. 
   
   A
   . Do you suspect central or nephrogenic diabetes insipidus? Why? How would you confirm the diagnosis?


2. 
   
   B
   . How does lithium cause diabetes insipidus?


3. 
   
   C
   . What is the cause of this patient’s polyuria? His thirst?


4. 
   
   D
   . What might occur if this patient were unable to maintain sufficient water intake?