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Comments, Opinions, and Brief Case Reports
November 26, 2001

Platelet Gigantism Associated With Cholestyramine Therapy

Arch Intern Med. 2001;161(21):2619-2620. doi:

Although cholestyramine has been widely prescribed for many years in the treatment of hypercholesterolemia, to our knowledge there have been no reports of platelet disorder induced by this drug. We report a case of platelet gigantism in a child receiving treatment with cholestyramine.

A 9-year-old boy with no medical history was treated with cholestyramine for hypercholesterolemia (cholesterol level, 446 mg/dL [11.51 mmol/L]) and type IIa hyperlipoproteinemia associated with cutaneous xanthoma. Three months later, an isolated thrombocytopenia (platelet count, 94 × 103/µL [94 × 109/L]) without any bleeding was observed. Treatment with cholestyramine was stopped, and his platelet count had apparently increased to the reference value. Cholestyramine therapy was reintroduced twice, and apparent thrombocytopenia rapidly recurred (over the first months). A hematological evaluation was eventually carried out in our laboratory while the child was receiving treatment. His platelet count had apparently decreased to 97 × 103/µL (97 × 109/L) according to both automated analyzers, Technicon H*2 (Bayer Diagnostics, Tarrytown, NY) and Coulter STKS (Beckman Coulter Inc, Fullerton, Calif). However, a log-normal curve of volume distribution could not be generated (Figure 1, A). Findings from a May-Grünwald-Giemsa (MGG)–stained blood smear analysis revealed large and giant platelets (Figure 1, B-C). The other blood cells appeared unaltered. Moreover, the platelet count according to the contrast phase microscopy (Unopette Microcollection System; Becton Dickinson Vacutainer Systems, Becton, Dickinson and Company, Franklin Lakes, NJ) after dilution was within the normal range (198 × 103/µL) [198 × 109/L]). We concluded that this was a spurious thrombocytopenia due to the presence of platelets of abnormally increased volume that were not detected by automatic particle counters. Platelet aggregation (turbidimetry) was normal with levels of adenosine diphosphate at 10 µmol/L, epinephrine at 5 µmol/L, collagen at 2 µg/mL, and ristocetin at 1.5 mg/mL. Findings from the MGG-stained bone marrow showed many megacaryocytes without any qualitative anomaly of the 3 hematopoietic lineages. Blood cell counts were normal in both parents, suggesting that an inherited giant platelet disorder was not present.

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