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Old 11-04-2010
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Question question_ central diabetes insipidus

PATIENT PROFILE - 18 yo female, nursing student employed at pediatric’s office, urinating every hour and drinking > 5 liters water daily, carries water bottle with her and drinks almost constatntly, physical exam unremarkable, bp 109/74, pulse 84, visual fields normal. Labs – serum Na 145, osmolarity 302 mOsm/L, fasting glucose 90. Urine osmolarity 70, glucose negative. 2-hour deprivation test à Uosm remains same at 70, Posm (plasma osmolarity) increases to 325. dDAVP subcutaneous injection raises Uosm to 500 and Posm to 286.
RELEVANT HX – no hx of head injury, mri rules out brain tumor
CURRENT MANAGEMENT – Rx with dDAVP nasal spray. As long as patientuses nasal spray, her urine output is normal, and she does not feel thirsty
QUESTION – why was dDAVP effective in treating her central diabetes insipidus?

I like to ask subsequent questions based upon the answer.
Objective being to LEARN EVERYTHING about diabetes insipidus with this scenario.
Also please advise me if it is ‘appropriate’ to upload relevant graphics
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Old 11-04-2010
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A quick answer:

There's 2 types of Diabetes Insipidus (DI)- Central and Nephrogenic.
Central DI- The posterior pituiatary fails to secrete ADH.
Nephro DI- The kidneys fail to respond to the circulating ADH.

So if you give an injection of dDAVP and the person responds you know its Central.

If you give an injection of dDAVP and the person stays the same you know its Nephrogenic
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Old 11-04-2010
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Exactly - the problem is that there is not enough ADH for some reason - usually difficult to determine but TB / tumors / surgery are some causes. So, the nasal spray replaces the ADH - problem solved
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