WBR0212
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| Author | PageAuthor::Vendhan Ramanujam |
|---|---|
| Exam Type | ExamType::USMLE Step 3 |
| Main Category | MainCategory::Community Medical Health Center, MainCategory::Primary Care Office, MainCategory::Inpatient Facilities |
| Sub Category | SubCategory::Endocrine, SubCategory::Electrolytes |
| Prompt | [[Prompt::A 84 year old man is referred from his nursing home for evaluation of confusion and lethargy. He is a known rheumatoid arthritis patient, who is currently using indomethacin and methotrexate. His temperature is 36.8 C, pulse is 72/min, blood pressure is 110/70 mm Hg and respirations are 16/min. He is disoriented. Mucus membranes are moist. Neck examination reveals no jugular venous distension. Lungs are clear on auscultation. Abdomen is soft, nontender and not distended. His laboratory results are significant for a serum sodium level of 118 mEq/L (Normal 135 mEq/L to 148 mEq/L). Other test results are Potassium 3.9 mEq/L |
| Answer A | AnswerA::Mineralocorticoid deficiency |
| Answer A Explanation | [[AnswerAExp::Incorrect-Mineralocorticoid deficiency will usually lead to hypovolemic hypotonic hyponatremia. Potassium levels will be high.]] |
| Answer B | AnswerB::Advanced renal failure |
| Answer B Explanation | [[AnswerBExp::Incorrect-Advanced renal failure will lead to hypervolemia hypervolemic hypotonic hyponatremia. Serum BUN and uric acid levels will be elevated.]] |
| Answer C | AnswerC::SIADH |
| Answer C Explanation | [[AnswerCExp::Correct-The patient has a euvolemic hypotonic hyponatremia secondary to inappropriate antidiuretic hormone secretion (SIADH). SIADH has a persistently elevated ADH level in the absence of an appropriate stimulus. NSAID’s potentiate the action of ADH and thus it is a cause of SIADH. Before SIADH diagnosis, it is appropriate to rule out hypothyroidism and adrenal insufficiency. The diagnostic test is the simultaneous measurement of serum and urine osmolality, which will be low (<285 mOsm/Kg of water) and inappropriately high (>300 mOsm/Kg of water) respectively. The low serum uric acid (<3.6 mg/dl in men) is due to hemodilution.]] |
| Answer D | AnswerD::Nephrogenic diabetes insipidus |
| Answer D Explanation | [[AnswerDExp::Incorrect-Nephrogenic diabetes insipidus will lead to polyuria, polydipsia, hypernatremia, high serum osmolality and low urine osmolality.]] |
| Answer E | AnswerE::Neurogenic diabetes insipidus |
| Answer E Explanation | [[AnswerEExp::Incorrect-Neurogenic diabetes insipidus will lead to polyuria, polydipsia, hypernatremia, high serum osmolality and low urine osmolality.]] |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The patient has a euvolemic hypotonic hyponatremia secondary to inappropriate antidiuretic hormone secretion (SIADH). SIADH has a persistently elevated ADH level in the absence of an appropriate stimulus. NSAID’s potentiate the action of ADH and thus it is a cause of SIADH. Before SIADH diagnosis, it is appropriate to rule out hypothyroidism and adrenal insufficiency. The diagnostic test is the simultaneous measurement of serum and urine osmolality, which will be low (<285 mOsm/Kg of water) and inappropriately high (>300 mOsm/Kg of water) respectively. The low serum uric acid (<3.6 mg/dl in men) is due to hemodilution.
Educational objective:
SIADH is characterized by a hypotonic hyponatremia with euvolemia and is accompanied by low serum osmolality (<285 mOsm/Kg of water) and high urine osmolality (>300 mOsm/Kg of water). |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |