WBR0198
| Author | PageAuthor::Vendhan Ramanujam |
|---|---|
| Exam Type | ExamType::USMLE Step 3 |
| Main Category | MainCategory::Inpatient Facilities |
| Sub Category | SubCategory::Gastrointestinal, SubCategory::Gastrointestinal, SubCategory::Electrolytes |
| Prompt | [[Prompt::A 54 year old woman, a known Crohn’s disease patient looking malnourished was admitted following severe diarrhea. She also has a small intestinal fistula. She was then started on parental nutrition. During the second week of parenteral nutrition, she develops spasms in her hands and feet. She also complains of muscle twitching and cramps. Examination reveals extension of interphalangeal joints and adduction and flexion of the metacarpophalangeal joints. The laboratory findings include Serum calcium 8.2 mg/dL |
| Answer A | AnswerA::Hyperventilation |
| Answer A Explanation | [[AnswerAExp::Incorrect-Normal blood pH and arterial PaCO2 rules out hyperventilation.]] |
| Answer B | AnswerB::Hypocalcemia |
| Answer B Explanation | [[AnswerBExp::Incorrect-The serum calcium in this patient is normal when adjusted for the low albumin. Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]), where 4.0 represents the average albumin level in g/dL. In other words, each 1 g/dL decrease of albumin will decrease 0.8 mg/dL in measured serum calcium and thus 0.8 must be added to the measured calcium to get a corrected calcium value. Hypomagnesemia would also cause functional hypoparathyroidism, which can lower serum calcium and thus result in a combined defect.]] |
| Answer C | AnswerC::Essential fatty acid deficiency |
| Answer C Explanation | [[AnswerCExp::Incorrect-It does not manifest as tetany.]] |
| Answer D | AnswerD::Focal seizure |
| Answer D Explanation | [[AnswerDExp::Incorrect-Focal seizures can focally involve the hands where the hands become stiff and associated with drawing movements. But they do not manifest as spasms typically described above.]] |
| Answer E | AnswerE::Hypomagnesemia |
| Answer E Explanation | [[AnswerEExp::Correct-Magnesium deficiency is common in malnourished patients and patients with large gastrointestinal fluid losses. The neuromuscular effects resemble those of calcium deficiency namely, paresthesia, hyperreflexia, muscle spasm, and ultimately tetany. But the cardiac effects are more like those of hypercalcemia. Thus an electrocardiogram serves as a rapid means of differentiating between hypocalcemia and hypomagnesemia. Hypomagnesemia also causes potassium wasting by the kidney. Many hospital patients with refractory hypocalcemia will be found to be magnesium deficient. Often this deficiency becomes manifest during the response to parenteral nutrition when normal cellular ionic gradients are restored.]] |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation::Magnesium deficiency is common in malnourished patients and patients with large gastrointestinal fluid losses. The neuromuscular effects resemble those of calcium deficiency namely, paresthesia, hyperreflexia, muscle spasm, and ultimately tetany. But the cardiac effects are more like those of hypercalcemia. Hypomagnesemia also causes potassium wasting by the kidney. Many hospital patients with refractory hypocalcemia will be found to be magnesium deficient. In case of low albumin levels, calcium has to be corrected to look for the actual calcium level.
Educational Objective:
Magnesium deficiency has neuromuscular effects that resemble those of calcium deficiency namely, paresthesia, hyperreflexia, muscle spasm, and ultimately tetany. But the cardiac effects are more like those of hypercalcemia. Thus an electrocardiogram serves as a rapid means of differentiating between hypocalcemia and hypomagnesemia. Hypomagnesemia also causes potassium wasting by the kidney. Many hospital patients with refractory hypocalcemia will be found to be magnesium deficient. |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |