|
Acquired Platelet Function Disorders |  |
| Dogs with immune-mediated thrombocytopenia also may have an acquired platelet functional defect. Dogs can have excessive bleeding tendencies without severely decreased platelet concentrations. In dogs with immune-mediated thrombocytopenia, abnormal platelet function in addition to decreased platelet concentration may contribute to their bleeding tendency. |
| Several diseases have been associated with acquired platelet function disorders. Hyperglobulinemia associated with multiple myeloma induces a platelet membrane defect resulting in impaired hemostatic function. In uremia associated with any form of renal disease, platelet adhesion and aggregation are decreased. Quantitative platelet disorders have been reported in liver disease with or without coagulation protein deficiencies. In 2 studies of cats with thrombocytopenia, 29-50% had
infectious diseases, including feline leukemia, feline infectious peritonitis, panleukopenia, or toxoplasmosis. The mechanism of thrombocytopenia has not been identified in many cases. Feline leukemia virus replicates and accumulates in megakaryocytes and platelets; aplasia or hypoplasia of marrow stem cells, immune-destruction of infected platelets, or extravascular sequestration of platelets within lymphoid tissues may contribute to thrombocytopenia in this disease. |
| Numerous drugs can impair platelet function. Drugs reported to block platelet receptor binding or to change platelet membrane charge or permeability include furosemide, penicillin, carbenicillin, lidocaine, phentolamine, and chlorpromazine. Drugs that inhibit transduction of messages received at the platelet surface include caffeine, theophylline, dipyridamole, and papavarine. Drugs that inhibit execution of platelet responses (aggregation, secretion, or thromboxane production)
include aspirin, indomethacin, acetaminophen, phenylbutazone, ticlopidine, pentobarbital, and sulfinpyrazone. Clinical bleeding problems may not be caused by drug-induced impairment of platelet function unless another disorder associated with a hemostatic defect is also present. |
