Lecture 30-Diabetes Insipidus Case

Question 1

What are polyuria causing disorders?

Answer 1

• primary polydipsia
• osmoreceptor dysfunction
• osmotic diuresis: diabetes mellitus
• Diabetes insipidus: central, nephrogenic, gestational

Question 2

When is AVP released?

Answer 2

in response to anything indicating low blood volume or high osmolarity:

• angiotensin
• hypovolemia
• hyperosmolality

Question 3

AVP release is inhibited when?

Answer 3

In response to baroreceptor activation (high blood pressure) and ANPs

Question 4

What are the causes of neurogenic (central) DI?

Answer 4

• 40-50% are from HYPOTHALAMIC tumors,
• -> PITUITARY tumors are usually insufficient to cause DI until post-op
• 20-30% are idiopathic (autoimmune, histiocytosis, sarcoidosis)
• <5% are genetic and are usually late onset

Question 5

What are the causes of nephrogenic DI?

Answer 5

familial mutations:

• either x-linked recessive V2 R mutation
• autosomal dominant AQP2 mutation

acquired:

• hypercalcemia (Ca > 13)
• hypokalemia (K < 2.5)
• drugs like lithium or demeclocycline

Question 6

What are the 2 types of primary polydipsia?

Answer 6

• dipsogenic

- psychogenic

Question 7

Explain dipsogenic DI.

Answer 7

resetting thirst threshold usually a result of granulomatus disease, iopathic reasons, age, mass lesions

Question 8

Explain psychogenic DI.

Answer 8

drinking for reasons other than thirst. Commonly seen in schizophrenic patients–called PIP: psychosis-intermittent hyponatremic polydipsia syndrome.

Question 9

What is characteristic of DI? Which criteria must be met for a DI diagnosis?

Answer 9

• characterized by hypotonic polyuria
• > 50 ml/kg in 24 hr period
• Uosm <300 mOsm/kg
• no solute diuresis (urine negative for glucose)
  and must show hypotonic urine in the presence of hyperosmolar serum

Question 10

What are the cutoffs for diagnosis of DI with the outpatient method?

Answer 10

• > 800 mOsm/kg rules it out, >600 mOsm/kg usually rules it out
• serum [Na] will also be tested

Question 11

What is the methodology of testing for DI with inpatient testing?

Answer 11

• measure urine and plasma osm until:
  
  • body water decreases by 3-5%
  • Uosm plateaus for 2-3 measurements
  • [Na] >145 and still outputting hypotonic urine
• administer dDAVP/AVP to distinguish btw central and nephrogenic DI
• Central: Uosm will increase by >50% of Uosm
• nephrogenic: Uosm will increase by <10% of Uosm

Question 12

Why does dDAVP not help someone with primary polydipsia?

Answer 12

• they have completely downregulated all of their AQP2 because they’re drinking in excess of 50 ml/kg
• They have disrupted the gradient between the cells and the collecting duct lumen so there is less of a driving force to pull water in.

Question 13

When can plasma AVP differentiate CDI from other polyurias?

Answer 13

• when Posm is >295 mOsm/kg

Question 14

What are chloropropamide, indomethicin, and carbomazepine?

Answer 14

All anti-diuresis enhancing agents

Question 15

What is used to treat DI

Answer 15

• water
• antidiuretics (AVP, dDAVP)
• anti-diuresis enhancing agents (chloropropamide, carbomazepine, indomethacin)