Heparin-induced thrombocytopenia: historical review

An Unusual Case of Thrombocytopenia and Leukopenia Associated with Diltiazem and Acyclovir

Objective:

To describe the case of a patient who developed thrombocytopenia associated with diltiazem and leukopenia associated with diltiazem or acyclovir.

Case Summary:

An 81-year-old white man was admitted for management of chronic obstructive pulmonary disease (COPD). On admission, his white blood cell (WBC) count and platelet count were within normal limits. Admission medications included metoprolol, which was replaced on day 3 with diltiazem due to concern that it might exacerbate the COPD. The patient's platelet count at the initiation of diltiazem therapy was 180 × 103/mm3. The next day the platelet count was 232 × 103/mm3, but decreased to 182 × 103/mm3 on day 5 and continued to decline through day 30, at which time it reached a nadir of 10 × 103/mm3. By then, several causes of thrombocytopenia, including disseminated intravascular coagulation and thrombotic thrombocytopenic purpura, had been ruled out. A hematology consult suggested diltiazem as the cause of thrombocytopenia, and it was discontinued. The platelet count began to rise 8 days after discontinuation of diltiazem and returned to normal values over a period of 5 days. On day 15, acyclovir was initiated for an oral herpes simplex virus–1 infection. The WBC count on day 20 was 8.7 × 103/mm3, and it continued to decline daily. On day 24, the value was 2.5 × 103/mm3, at which time acyclovir was discontinued. The WBC count continued to decline for 6 days, reaching a nadir of 0.6 × 103/mm3, at which point filgrastim was initiated; the WBC count gradually returned to normal over the next 5 days.

Conclusions:

Myelosuppression is a rare complication of diltiazem and acyclovir therapy. Patients using these medications should be monitored for signs and symptoms of myelosuppression.

Use of recombinant hirudin in heparin-induced thrombocytopenia and thrombosis (HITT) and renal failure--a case report

Treatment of critically ill patients who have heparin-induced thrombocytopenia and thrombosis (HITT) and also renal failure is a challenge. Recombinant hirudin (Refludan, Hoechst Marion Roussel) is a direct thrombin inhibitor indicated for anticoagulation in HITT and approved by the United States Food and Drug Administration. Because this drug is renally cleared, a single dose of hirudin may induce prolonged (up to one week) unpredictable anticoagulation in patients with renal insufficiency. There are a few case reports of patients with renal failure and suspected heparin-induced thrombocytopenia (HIT) in which patients were anticoagulated with Refludan for catheter thrombosis. There is no literature on the therapeutic use of Refludan to treat HITT in patients with diffuse thrombosis and renal failure. The authors report the case of a 44-year-old female dialysis patient with HITT and extensive life-threatening thrombosis. The patient developed common iliac vein occlusion extending to the right atrium with progressive right internal jugular vein thrombus developing while on heparin. Her platelet count dropped to 60,000/microL. She was lethargic and hemodynamically unstable. Refludan was initially given as a bolus of 0.2 mg/kg (total, 12 mg) at a 50% dose reduction based on the patient's ideal body weight. This dose was based on the published pharmacokinetics of Refludan in patients with renal failure. Only 2 additional boluses of 6 mg and 3 mg were needed to extend the duration of therapeutic anticoagulation (measured by PTT) to 140 hours. The patient improved both clinically and radiographically after the treatment with Refludan. There were no additional thromboembolic events or bleeding complications. The platelets returned to normal within a few days. The patient was transitioned to coumadin and discharged from the hospital. She remains stable at 1-year follow-up.

Mechanisms of venous and arterial thrombosis in heparin-induced thrombocytopenia

Since the reports by Weismann and Tobin in 1958 and Roberts et al. in 1964 called attention to paradoxical thrombosis in patients treated with heparin, the thrombotic aspect of the heparin-induced thrombocytopenia syndrome (HIT) has been emphasized. Yet to this day, the mechanism of thrombosis associated with HIT (HITT) is unclear. It is important to understand the etiology of HITT because of its devastating clinical consequences. We believe one rational approach to understand the mechanism underlying HITTS is to invoke Virchow's triad: stasis, vascular injury and a hypercoagulable state. A hypercoagulable state exists in all HIT patients due to platelet activation by heparin antibody binding. Thrombin generation from platelet microparticles and exposed platelet phospholipid, coupled with stasis (elderly bedridden or otherwise sedentary ill patients who comprise the majority of the HIT population), provide two risk factors that can lead to venous thrombosis. A hypercoagulable state coupled with endothelial cell dysfunction due to injury from heparin antibody, activated platelets, leukocytes, platelet microparticles, complement, atherosclerosis or medical intervention can lead to arterial thrombosis. Of patients with HIT, HITT occurs in about 25%, suggesting that a second set of patient specific risk factors, in addition to the generation of pathological heparin antibodies, determine whether HITT will develop. Interaction between activated platelets and other platelets, and with endothelial cells, leukocytes, neutrophils, monocytes and cytokines are areas of research that may provide more specific characterization of the hypercoagulable state and vascular damage. Nuances involving genetic variation in platelets, endothelial cells and immune function are also likely to be a major component of the observed variability of this disease spectrum. Virchow's triad may explain the different manifestations of HITTS.