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A 38-year-old male patien t is evaluated for fatigue. He has no other specific com-plaints; he den ies fever. chills. abdomi nal pain. and urinary symptoms. Family history includes a brother who died at age of 8 years of renal failure. Complete blood count shows leukocyte count of 7 . 800/ J.LL. hemoglobin 8.9 g/dl. and platelet count 9.000/ J.LL. Creatinine is 7.9 mg/dl. LDH is 2200 U/L. The peripheral blood smear is shown below.
This peripheral blood smear would be consistent with all of the following conditions except:
- Thrombotic-thrombocytopenic purpura (TTP)
- Malignant hypertension
- Autoimmune hemolytic anemia (AIHA)
- Disseminated intravascular coagulation (DIC)
- Hemolytic uremic syndrome (HUS)
Medicine
C. The peripheral smear is notable for the presence of schistocytes and thrombocytopenia. Schistocytes are characteristic of conditions associated with microangiopathic hemolytic anemia (MAHA). MAHA has been noted in patients with malignant hypertension, DIC, HUS, and several other disorders. However, MAHA is not usually observed in autoimmune hemolytic anemia, which is characterized by spherocytes in the peripheral blood smear. The clinical findings of MAHA, thrombo-cytopenia, renal failure, and a family history of renal failure in a sibling who died at a young age aroused suspicion for atypical HUS. Additional studies revealed a deficiency of complement factor H ( CFH), the plasma regulator of the alternate pathway, in the patient. Approximately 10% of cases of the HUS are classified as atypical, and less than 20% of cases of atypical HUS are familial. Mutations in CFH have a reported frequency of 40% to 45% of patients with familial atypical HUS. Gene mutations involving the complement regulatory proteins result in excessive complement activation, endothelial cell damage, and local accumulation of platelet-fibrin thrombi.
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