WBR0978
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::Neurology |
| Prompt | [[Prompt::A 73-year-old female with history of poorly controlled diabetes mellitus type 2 since 20 years presents for increased tenderness in her left foot. The foot is warm, erythematous and tender. An ulcer involving the full thickness of the skin in noted in the foot. The patient is informed that her condition is a complication of her poorly controlled diabetes resulting from vascular and peripheral nerve damage. Deficiency of which of the following enzymes in nerve cells is responsible for the neuropathy associated with diabetes?]] |
| Answer A | AnswerA::Aldose reductase |
| Answer A Explanation | AnswerAExp::Aldose reductase is not lacking in schwan cells. Neuropathy is the result of the osmotic damage seen in poorly controlled diabetes due to the absence of sorbitol dehydrogenase in the schwann cells. |
| Answer B | AnswerB::Sorbitol dehydrogenase |
| Answer B Explanation | AnswerBExp::Neuropathy is the result of the osmotic damage seen in poorly controlled diabetes due to the absence of sorbitol dehydrogenase in the schwann cells. |
| Answer C | AnswerC::Aldolase B |
| Answer C Explanation | [[AnswerCExp::Neuropathy is the result of the osmotic damage seen in poorly controlled diabetes due to the absence of sorbitol dehydrogenase in the schwann cells. Aldolase B is not involved in the sorbitol metabolism. Aldolase B is involved in the fructose metabolism.]] |
| Answer D | AnswerD::Triose kinase |
| Answer D Explanation | [[AnswerDExp::Neuropathy is the result of the osmotic damage seen in poorly controlled diabetes due to the absence of sorbitol dehydrogenase in the schwann cells. Triose kinase is not involved in the sorbitol metabolism. Triose kinase is involved in the fructose metabolism.]] |
| Answer E | AnswerE::NADPH oxidase |
| Answer E Explanation | AnswerEExp::Aldolase B is not involved in the sorbitol metabolism. Aldolase B is involved in the fructose metabolism. NADPH oxidase is not involved in the sorbitol metabolism. |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::The patient presents with a foot ulcer and swelling, erythema and tenderness in her left foot. The patient's signs and symptoms are consistent with an infected diabetic foot. The diabetic foot is a complication of diabetes seen among patients with poorly controlled diabetes. Diabetic foot results from vasculopathy and neuropathy. The neuropathy in diabetics is the consequence of the osmotic damage of the sugars to the schwann cells. Glucose is converted in cells to sorbitol; when glucose is very elevated, sorbitol accumulates in the cells that can not degrade it and cause osmotic damage. Schwann cells lack sorbitol dehydrogenase which converts sorbitol to fructose. Shown below is a diagram depicting the sorbitol metabolism.
Educational objective: Glucose is converted to sorbitol which cause osmotic damage when it accumulates in cells lacking sorbitol dehydrogenase. Neuropathy is the result of the osmotic damage seen in poorly controlled diabetes. Reference:
First aid for USMLE step 1, 2013. Page 105. |
| Approved | Approved::No |
| Keyword | WBRKeyword::Sorbitol, WBRKeyword::sorbitol dehydrogenase, WBRKeyword::diabetic neuropathy |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
