Inappropriate bruising or bleeding arises in animals for many reasons, including disorders associated with platelets, clotting factors, or the vessels in which blood travels. These disorders are not common, but can occur in any age or breed of dog.

Bruising or bleeding may occur in association with many systemic illnesses or disorders. Clinical signs may be mild and subtle, such as a small bruise on the skin, or signs may be severe and life threatening. Unexplained or abnormal bruising or bleeding should never be ignored. Examination by a veterinarian should be sought immediately in pets that appear to be pale, lethargic, weak, or in distress.

When evaluating an animal with abnormal bleeding, it is important to establish a definitive diagnosis as to the type of clotting abnormality present, and to identify any underlying causes. The therapy of coagulopathies varies, and must address not only the underlying cause, but must also treat the specific defect in clotting.

Causes

There are many causes of bruising and bleeding. Although it is not unusual for a normal cat or dog to have a small bruise or an occasional fleck of blood in the stool, it is not normal or acceptable for bleeding to be widespread, prolonged, severe, or recurrent.

Platelet disorders are the most common disorders associated with bleeding or bruising. Platelet disorders can arise when platelet numbers are decreased or when platelets fail to function properly. Platelet numbers are decreased when they are not produced adequately in the bone marrow, when they are destroyed, or when they are prematurely removed from the circulation. Thrombocytopenia is defined as a decreased platelet count. Generally speaking, animals with platelet counts less than 25,000 may bleed spontaneously and are at risk for life-threatening hemorrhages.

Dysfunction of platelets can occur as an inherited, congenital disorder, or may develop as an acquired condition later in life.

Disorders that Decrease Platelet Numbers or Function

Immune mediated destruction of circulating platelets or the cells of the bone marrow that form platelets

Various disorders of the cells of the bone marrow, such as cancer, myelophthisis and myelofibrosis

Viral infections – canine distemper virus, parvovirus

Bacterial infections – Salmonella

Rickettsial infections – ehrlichiosis

Certain parasites – heartworm disease, Plasmodium infection

Neoplasia (cancer) in the body

Drugs that alter platelet production or function – estrogen, trimethoprim/sulfas, chemotherapeutic drugs, phenylbutazone, aspirin and other nonsteroidal anti-inflammatory drugs, azathioprine, albendazole, etc.

Hormonal imbalances, such as excessive production of estrogen as seen in hypothyroidism

Disorders of the spleen

Vasculitis (inflammation of the vessels)

Disseminated intravascular hemolysis (DIC), a complex, life threatening hemostatic defect that occurs secondary to many systemic diseases

Congenital platelet function disorders of the basset hound, foxhound, otterhound, Great Pyrenees, Scottish terrier, etc.

Kidney disease

Liver disease

Vaccination with modified live viruses

Vascular Disorders

Vasculitis – inflammation of blood vessels

Hyperadrenocorticism – a disease where the adrenal glands produce too much cortisone hormone in the body

Diabetes mellitus – sugar diabetes

Uremia – an increase in waste products not cleared by diseased kidneys

Clotting Factor Disorders

Inherited deficiencies of clotting factors that result in hemophilia        

Toxicity with warfarin or warfarin-like products that antagonize Vitamin K         

Liver disease that prevents the manufacture of clotting factors

Disseminated intravascular coagulation (DIC), which is widespread bleeding due to the consumption of platelets and clotting factors

Von Willebrand's disease, which arises from a deficiency of a factor needed for proper platelet function