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Are you studying for the step exams or the shelf? Want to see many examples of the same condition in one place so you don't have to wait days to have concepts reinforced? If this sounds like you check out my posts! This post is on Diabetes Insipidus.
Ok everyone diabetes insipidus (DI) is a very high yield topic for the boards! I strongly encourage you all to make yourselves familiar with this topic (and how it shows up on the exam). Nothing is actually that complicated when you look at the patterns, but I think DI has a bit of a history of tripping people up because there are all these osmolaities and nonsense involved.
Because there are 2 types of DI, lets first focus on how you can tell you are dealing with DI, then we will stratify by type.
KEY FEATURES OF DI ON EXAMS:
1.) Increased urination and thirst: this is going to show up every single time. It will be the first pieces of information you get. Now at this point you won’t know if this is diabetes, psychogenic polydipsia etc, however if you see increased urination and thirst then you must consider DI.
2.) Serum values: patients will have hypernatremia, increased serum osmolality and normal glucose. This will make sense because free water is lost by the body, and helps differentiate this condition from psychogenic polydipsia (where you have hyponatremia) and diabetes (given normal glucose levels). With the history above and these values you should feel pretty confident about a DI diagnosis but there will be more details.
3.) Urine values: urine osmolality and/or specific gravity will be low because so much free water is present. An important key point is that water deprivation will NOT concentrate the urine (such as in psychogenic polydypsia) because the body has lost the ability absorb free water in the setting of dehydration.
With the symptoms, serum values, and urine values you can very confidently make the diagnosis of DI. But now lets just spend some time discussing central vs. nephrogenic.
CENTRAL DI FEATURES
1.) History: patients may have a history of head trauma, cranial surgery (anything that might explain damage to the central hormone axis present in the brain). Sometimes the absence of a history that would explain nephrogenic DI makes us assume a central cause.
2.) Urine concentrates in response to desmopressin: if a patient is given ADH/desmopressin and their urine concentrates (increased osmolality) then we can be confident that the DI is central.
NEPHROGENIC DI FEATURES
1.) History: patients typically have a history of bipolar disorder that is treated with lithium. This will be the cause of the nephrogenic DI.
2.) Urine does not concentrates in response to desmopressin: because the issue is with how the kidney responds to ADH, desmopressin administration will not do anything.
Sorry for the long post! Take a look at the questions I think it is well worth it!
I can't post links just yet (just started on SDN) but go to the website stepwards and search Diabetes Insipidus to find the archive of questions that this post corresponds to.
Ok everyone diabetes insipidus (DI) is a very high yield topic for the boards! I strongly encourage you all to make yourselves familiar with this topic (and how it shows up on the exam). Nothing is actually that complicated when you look at the patterns, but I think DI has a bit of a history of tripping people up because there are all these osmolaities and nonsense involved.
Because there are 2 types of DI, lets first focus on how you can tell you are dealing with DI, then we will stratify by type.
KEY FEATURES OF DI ON EXAMS:
1.) Increased urination and thirst: this is going to show up every single time. It will be the first pieces of information you get. Now at this point you won’t know if this is diabetes, psychogenic polydipsia etc, however if you see increased urination and thirst then you must consider DI.
2.) Serum values: patients will have hypernatremia, increased serum osmolality and normal glucose. This will make sense because free water is lost by the body, and helps differentiate this condition from psychogenic polydipsia (where you have hyponatremia) and diabetes (given normal glucose levels). With the history above and these values you should feel pretty confident about a DI diagnosis but there will be more details.
3.) Urine values: urine osmolality and/or specific gravity will be low because so much free water is present. An important key point is that water deprivation will NOT concentrate the urine (such as in psychogenic polydypsia) because the body has lost the ability absorb free water in the setting of dehydration.
With the symptoms, serum values, and urine values you can very confidently make the diagnosis of DI. But now lets just spend some time discussing central vs. nephrogenic.
CENTRAL DI FEATURES
1.) History: patients may have a history of head trauma, cranial surgery (anything that might explain damage to the central hormone axis present in the brain). Sometimes the absence of a history that would explain nephrogenic DI makes us assume a central cause.
2.) Urine concentrates in response to desmopressin: if a patient is given ADH/desmopressin and their urine concentrates (increased osmolality) then we can be confident that the DI is central.
NEPHROGENIC DI FEATURES
1.) History: patients typically have a history of bipolar disorder that is treated with lithium. This will be the cause of the nephrogenic DI.
2.) Urine does not concentrates in response to desmopressin: because the issue is with how the kidney responds to ADH, desmopressin administration will not do anything.
Sorry for the long post! Take a look at the questions I think it is well worth it!
I can't post links just yet (just started on SDN) but go to the website stepwards and search Diabetes Insipidus to find the archive of questions that this post corresponds to.
