Histology USMLE Step 1 Practice Question
A 3-year-old boy presents to the emergency department with epistaxis and petechiae after a minor fall. His mother reports he bruises easily and had prolonged bleeding after circumcision at 6 months of age. Vital signs are stable. Laboratory studies show: platelet count 245,000/μL (normal), bleeding time 15 minutes (normal <9 minutes), prothrombin time 12 seconds (normal), activated partial thromboplastin time 28 seconds (normal). Bone marrow examination reveals normal megakaryocytes with normal morphology and ploidy. Electron microscopy of peripheral blood platelets reveals sparse cytoplasmic organelles compared to normal controls. Which of the following histologic findings best explains this patient's bleeding disorder?
Answer choices
- AAbsence of alpha-granules with normal dense bodies (gray platelet syndrome)
- BIncreased number of mitochondria with enlarged platelet volume
- CMarkedly reduced dense granules with near-absent storage poolsCorrect answer
- DExcessive glycogen accumulation in the cytoplasmic matrix
- EProliferation of open canalicular system with preserved granule content
- FAbnormal cross-linking of microtubule cytoskeleton with normal granule morphology
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