Case 3
1. What is the cause of this patient’s polyuria?The cause of this patient's polyuria is diabetes insipidus.
This patient is unable to concentrate his urine due to a lack of AVP. His renal collecting system is intrinsically normal, but the responsible hormone to make this system operative is lacking.
The discussion of this should include the differential of polyuria (> 3 liters per day), including diabetes mellitus, hypokalemia, hypercalcemia, and an inability of the renal tubular system to respond to AVP or nephrogenic DI, in addition to psychogenic water drinking.
Causes of polyuria include
diabetes mellitus (ruled out by a normal glucose)
hypokalemia (ruled out by a normal potassium)
hypercalcemia (ruled out by a normal calcium)
excessive water ingestion (ruled out by borderline elevated BUN, serum sodium, and elevated serum osmolality),
nephrogenic diabetes insipidus (ruled out by an absent ADH level during maximum dehydration and the normal response to DDAVP administration)
central diabetes insipidus, which was the correct diagnosis.
2. When did the disease process begin?
The disease process began 18 months prior to his presentation.
The case should be expanded to include the patient's presentation of acute onset polyuria, which is characteristic of DI and the lack of any obvious etiology for this problem.
3. Explain the results of the water deprivation test.
During the water deprivation test, the patient was unable to concentrate his urine osmolality and continued to be polyuric after three hours of dehydration.
Once the patient was given AVP, he was immediately able to diminish his urine output and concentrate his urine successfully.
His dehydration is clearly manifest by his plasma osmolality of approximately 305.
4. Which symptoms or signs reflect which hormone deficiencies?
The signs and symptoms which reflect other hormone deficiencies include loss of body hair in the axilla, chest and pubic areas, reflecting loss of adrenal androgens; inability to shave and a soprano voice, in addition to his inability to develop muscles and lack of libido, all indicating lack of testosterone.
His inability to perform sexually could be attributable to a high prolactin and low gonadotropins.
The cessation of his growth would reflect growth hormone deficiency and his non-specific symptoms of tiredness and depression would be attributable to lack of cortisol and lack of thyroid hormone.
His past history of an automobile accident when switching lanes could reflect his visual field deficiency.
Physical findings
On physical exam, his bradycardia, depressed respiratory rate, and cool body temperature could be reflective of hypothyroidism.
His height of 65" may reflect growth hormone deficiency; however, this would need to be taken in context of his family height history.
His constricted visual fields reflect optic chiasm involvement from his enlarging pituitary mass.
His non-palpable thyroid would be indicative of lack of TSH stimulation.
The galactorrhea would reflect an elevated prolactin value.
His genitalia exam is abnormal due to lack of gonadotropins.
His cool, pale skin could be attributable to his hypothyroidism, as would be his delayed deep tendon reflexes.
Finally, lack of axillary and pubic hair would reflect low adrenal androgens and low testosterone.
5. What is the most likely pathology of this problem?
Craniopharyngioma
6. Where is the most likely site of the mass?
The hypothalamus and/or stalk
7. What mechanism could be responsible for the hyperprolactinemia?