This page is dedicated to organizing various examples of standardized exam questions whose answer is SIADH. While this may seem a odd practice, it is useful to see multiple examples of how SIADH will be characterized on standardized exams (namely the boards and the shelf exams). This page is not meant to be used as a tradition question bank (as all of the answers will be the same), however seeing the classic “test” characterization for a disease is quite valuable.
KEY CHARACTERISTICS OF THIS CONDITION (ON EXAMS)
When it comes to standardized exams, each topic has its own “code” marked by key buzzwords, lab findings, clues, etc. If you are well versed in this code you will be able to more quickly identify the condition that is being discussed, and get the right answer on the exam you are taking. Below is the “code” for SIADH.
Question # 1
A 25 year old male is brought to the hospital after he sustains an accident while riding his motorcycle. He hits his head however a CT scan of the cranium shows no abnormalities. 2 days later it is noticed that his serum sodium concentration is 120 mEq/L and his urine osmolality is found to be 350 mOsmol/kg. What is the likely diagnosis in this patient?
Explanation # 1
Head trauma + decreased serum sodium + increased urinary osmolality = SIADH
Question # 2
A 70 year old woman is brought to the hospital due to altered mental status. Her family explains that she awoke this morning with a headache and has been getting worse over the course of the day. The day before, she had vomited a few times during the day. A month ago, the patient was diagnosed with depression and began taking sertraline with a good response. Her only other medical problem is rheumatoid arthritis, which was diagnosed a year ago and has been controlled with adalimumab new man. She does not take any other medication and supplements or herbs. She does not have a fever. Her blood pressure is 120/70 mm Hg, her pulse is 75/10, and respirations are 15/min. The patient is disoriented however the physical exam is on remarkable. Lab results are as follows.
- Na+: 118 mEq/L ***
- K+: 4.1 mEq/L
- Bicarbonate: 25 mEq/L
- Blood glucose: 88 mg/dL
- BUN: 9.1 mg/dL
- Uric acid: 1.7 mg/dL
The patients serum osmolality 260 mOsm/kg, her urine osmolality is 505 mOsm/kg, and her urine sodium is 60 mmol/L. What is the likely diagnosis in this patient?
Explanation # 2
SSRI usage + decreased serum sodium + increased urinary osmolality = SIADH (secondary to sertraline usage
Question # 3
Explanation # 3
TESTABLE FACTS ABOUT THIS TOPIC (BEYOND ITS IDENTIFICATION)
Many questions on standardized exams go beyond simply recognizing the underlying topic. Often there are specific testable facts regarding some aspect of the topic’s pathophysiology/management/clinical implications that are commonly asked. Some of these are listed below:
- Fluid restriction
- IV hypertonic saline
- ADH antagonists (conivaptan, tolvaptan): these work to block activation of ADH by blocking the V2-receptor
- Demeclocycline: this is a tetracycline that is also a ADH antagonist
Page Updated: 01.22.2017