Issue Description Thrombocytopenia refers to an abnormally low
blood-concentration of platelets, which are blood cells that promote
blood clotting after injury to the lining of the blood vessels. When
the concentration of platelets becomes too low, bruising and bleeding
may occur. Dogs with blood platelet concentrations of less than 40,000
per microliter of blood are at risk for spontaneous bleeding.
Abnormally low platelet numbers in blood can be caused by a variety of
disease processes. These include failure to produce new platelets in
the bone marrow, premature destruction of circulating platelets often
by the body's own immune system, sequestration or storing of platelets
in organs, and consumption of platelets at a rate that exceeds
production in the bone marrow. Dogs of either gender, any age and any
breed can suffer from thrombocytopenia.
The severity of
bleeding associated with thrombocytopenia depends on how low the
platelet numbers fall.
Causes Decreased platelet counts can be due to a
number of disease processes:
Vitamin B12 or folic acid deficiency.
Leukemia or myelodysplastic syndrome.
Decreased production of thrombopoietin by the liver in liver
Sepsis, systemic viral or bacterial infection.
Dengue fever can cause thrombocytopenia by direct infection of
bone marrow megakaryocytes as well as immunological shortened platelet
Bernard-Soulier syndrome, associated with large platelets.
May Hegglin anomaly, the combination of thrombocytopenia,
pale-blue leuckocyte inclusions, and giant platelets.
Grey platelet syndrome
Idiopathic thrombocytopenic purpura (ITP)
Thrombotic thrombocytopenic purpura (TTP)
Hemolytic-uremic syndrome (HUS)
Disseminated intravascular coagulation (DIC)
Paroxysmal nocturnal hemoglobinuria (PNH)
Systemic lupus erythematosus (SLE)
Post transfusion purpura
Neonatal alloimmune thrombocytopenia (NAITP)
Splenic sequestration of platelets due to hypersplenism
Dengue fever has been shown to cause shortened platelet survival
and immunological platelet destruction
o Valproic acid
o Other chemotherapy drugs
Immunological Platelet Destruction
Drug binds Fab portion of an antibody. The
classic example of this mechanism is the quinidine group of drugs. The
Fc portion of the antibody molecule is not involved in the binding
Drug binds to Fc, and drug-antibody complex binds and activates
platelets. Heparin induced thrombocytopenia (HIT) is the classic
example of this phenomenon. In HIT, the heparin-antibody-platelet
factor 4 (PF4) complex binds to Fc receptors on the surface of the
platelet. Since Fc portion of the antibody is bound to the platelets,
they are not available to the Fc receptors of the reticulo-endothelial
cells, so therefore this system cannot destroy platelets as usual.
This may explain why severe thrombocytopenia is not a common feature
Symptoms The usual patient is a middle-aged dog. Poodles
appear to be predisposed though Cocker Spaniels and Old English
Sheepdogs also seem to have a higher than average incidence of this
Spontaneous bruising is the major clinical sign.
The gums and oral surfaces or on the whites of the eyes are a obvious
areas to check as is the hairless area of the belly. Small spots of
bruising in large conglomerations called "petecchiae" are the telltale
sign. A large, purple expansive bruise might also be seen called
"ecchymosis." Large internal bleeds are not typical of platelet
dysfunction, though bleeding small amounts in urine, from the nose, or
rectally may also indicate a platelet problem.
Diagnosis Inspection of gums and mouth, whites of the
eyes, and abdomen may reveal petechiae or ecchymosis. Blood platelet
counts can determine if numbers of platelets are normal or too low, or
appear abnormal. Tests are not yet available to detect anti-platelet
antibodies. Veterinarian diagnosis on a case-by-case basis, using
tests for other diseases combined with symptom assessment.