PLATELETOPATHIES

21 PLATELETOPATHIES



1 What is the clinical presentation of thrombocytopenia in dogs and cats?


The clinical impression of thrombocytopenia, thrombocytopathia, and endothelial cell problems cannot easily be differentiated based on clinical presentation. The only somewhat specific clinical signs are petechiae, purpura, and ecchymosis. This type of bleeding is often associated with mucous membranes or friction areas such as the axilla or inguinal areas. Other, nonspecific signs may include hematuria, epistaxis, hematochezia, and hemoptysis. Fever is often present in an actively bleeding animal. If the buccal mucosal bleeding time is prolonged in a dog or cat with appropriate platelet numbers, the prolongation is probably caused by thrombocytopathia or endothelial problems. Remember that thrombocytosis causes unpredictable clinical signs.



2 What is the buccal mucosal bleeding time?


The buccal mucosal bleeding time (BMBT) is used when platelet dysfunction (thrombocytopathia, von Willebrand’s disease) or endothelial cell dysfunction is suspected. In dogs or cats with platelet counts less than 70,000/μl, the BMBT is often prolonged. If petechiae are present, a BMBT will add no additional information and need not be performed because petechiae are specific for a primary system dysfunction. Therefore, in effect, the use of the BMBT is reserved for nonthrombocytopenic patients with evidence of primary hemostatic disorders. The patient is placed in lateral recumbency, and a firm (not tight) gauze tie is used to fold back and expose the buccal mucosa. Hand movement tends to affect the test, so a gauze tie is used. A nonvascular area is selected. A guillotine-like “bleeding time device” (e.g., Simplate II) is placed lightly on this area and triggered. A stopwatch is started. At 30-second intervals and without touching the wound, blood leaking from the wound is soaked up. The time from the creation of the minor incision(s) until blood stops flowing from the wound is the BMBT. In dogs and cats, the BMBT reference interval in my practice is 1.7 to 4.2 seconds. Most results are near the low end of the reference interval.



3 Can a “guarded” scalpel or the “toenail” bleeding time be used?


These “scalpel” and “toenail” tests should not be used. Although all these tests, including the BMBT, are somewhat crude, at least the BMBT has built-in controls; the other tests do not. The BMBT has withstood scientific scrutiny in the form of published articles in the veterinary literature.



4 Which etiologies should be considered with a thrombocytopenic patient?


Thrombocytopenia is seldom “idiopathic.” Not uncovering an etiology simply underlines limited diagnostic abilities as regards this common clinical presentation. Although platelet numbers can be affected by severe hemorrhage, thrombocytopenia is seldom severe and is usually >70,000 cells/μl. A careful history with specific questions regarding anticoagulant rodenticides, other drugs, recent vaccinations, and tick infestations is essential. An infectious or immune-mediated etiology is the most likely cause of thrombocytopenia. Serology for the common tick-borne diseases only examines the “tip of the iceberg.” In fact, unless a specific etiology is uncovered, 3 to 4 weeks of appropriate antimicrobial therapy is indicated in conjunction with other forms of therapy.



5 What do hemogram reports indicating the platelet count is “adequate” really mean?


The numbers of platelets associated with “adequate” platelet numbers do differ somewhat between laboratories, but this is a moot point. It is essential to obtain an actual platelet count by estimation, manual counts, or instrument counts obtained in the production of the hemogram. Ideally, the platelet count determined by the instrument should be corroborated by the technologist’s or clinical pathologist’s visual estimation; these should be in close agreement. This is somewhat problematic in feline hematology because more than 60% of feline blood specimens contain platelet clumps despite numerous efforts to stop clumping. The word “adequate” in relation to platelet counts in a patient without observable hemorrhage or suspected occult hemorrhage is usually satisfactory. All instrument-produced hemograms include a direct platelet count that may or may not actually be reported.



6 What does mean platelet volume mean?


The mean platelet volume (MPV) is the platelet equivalent of the red blood cell mean cell volume (MCV). An increased MPV indicates that mean platelet size is increased—the presence of macroplatelets. Macroplatelets are usually an indication of young or reactive platelets responding to increased thrombopoiesis—increased concentrations of thrombopoietin. (Apparently, macroplatelets are observed along with reduced platelet counts in Cavalier King Charles Spaniels.) A decreased MPV indicates decreased mean platelet size or presence of microplatelets. Microplatelets may be the only early indication of complement-mediated, immune-mediated attack against platelets.



7 Can bone marrow examination be accomplished when thrombocytopenia is severe?


Bone marrow aspiration or biopsy is necessary if the cause of the thrombocytopenia has not been ascertained. Any questionable cytopenias or multiple cell line cytopenias necessitate marrow examination to aid in determining etiology. Hemorrhage, if present at all with severely thrombocytopenic patients, is usually modest and easily controlled by pressure. Hemorrhage is uncommon or modest in thrombocytopenic patients in general. When platelet-related hemorrhage is observed and considered significant, both reduced platelet numbers and platelet dysfunctional states (a combination) are probable.

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Aug 26, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on PLATELETOPATHIES

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