Pet Health Library

Background

Thrombocytopenia refers to a disorder in which the patient has too few platelets.

Platelets are small cell-like particles in the blood, which are produced in the bone marrow. Their function is to form blood clots to stop the flow of blood after an injury or surgery. When platelet levels are very low, bleeding can occur.

Thrombocytopenia may occur as a response to a disease, as a component of blood cancer, immune disorder or as an adverse reaction to a medication. Since thrombocytopenia can be life-threatening, early detection and intervention are key.

There are two types of thrombocytopenia: congenital (present at birth) or acquired. Acquired thrombocytopenia can occur in dogs and cats and can have many causes.

Risk Factors

• Genetic Predisposition – Some dog breeds genetically have fewer platelets, such as the Cavalier King Charles Spaniel, Norfolk and Cairn terriers, Shiba Inu, and Greyhound.  Bleeding from low platelets is uncommon in these breeds. They do not require treatment for this disorder.
• Infections
  • Viral – Canine parvovirus infection damages the bone marrow and decreases platelet production.  Canine distemper virus, feline leukemia virus and feline immunodeficiency virus are other causes of thrombocytopenia.
  • Bacterial or fungal infections can lead to platelet destruction.
  • Tick-borne infections ehrlichiosis, anaplasmosis and Rocky Mountain spotted fever lead to platelet destruction.
• Neoplasia (Cancer) – Cancer can cause thrombocytopenia if a bleeding tumor uses up all the platelets, if a cancer takes over the bone marrow and platelet production is decreased or cancer can cause immune destruction of platelets.
• Immune-mediated Diseases – Known as immune thrombocytopenia (ITP), ITP is caused when the animal’s own immune system destroys the platelets or platelet-producing cells in the bone marrow. ITP is categorized as secondary when there is an underlying disease triggering the destruction, or primary when no other cause is present.
• Treatment-related – Caused by some drugs and classes of drugs (like estrogen and some antibiotics and chemotherapy drugs) that suppress platelet production in the bone marrow, or drugs (like penicillin, sulfa antibiotics, methimazole, and others) that destroy the platelets circulating in the bloodstream. These cases are rare and unpredictable, and platelets usually return to normal after discontinuing the drug(s).

Diagnosis

Your veterinarian will suspect thrombocytopenia when they see the clinical signs described above.  To confirm thrombocytopenia and its cause, your veterinarian will begin with a thorough history and physical examination. Your doctor will start by asking about your pet’s recent vaccination history, medication intake, and outdoor activities. This is all very important to determine the treatment plan.

After the physical examination and history check, a blood sample will be obtained to perform a platelet count. This analysis can reveal key information, such as:

• If the platelets are broken up into fragments, signaling an autoimmune reaction
• The presence of a recognizable, breed-specific disease
• The presence of any infectious diseases
• Evidence of cancer

Additional diagnostics may be carried out afterwards, such as an x-ray and ultrasound, analysis of a bone marrow sample, biopsy, testing for tick-borne diseases, and tests assessing blood clotting.

Presently, immune thrombocytopenia (ITP) in dogs and cats is a diagnosis of exclusion. This means a diagnosis of ITP is made if the tests for all other causes of thrombocytopenia are negative. There is no specific diagnostic test for ITP.

Treatment

Treatments According to Cause of Thrombocytopenia

• Infection –Specific treatment depends on the type of infection.
• Other diseases – The underlying disease is treated appropriately.
• Immune Thrombocytopenia (ITP) – Corticosteroids are the usual treatment, although other drugs are used. If the patient has repeated episodes, spleen removal may be considered. ITP cannot always be cured, but the patient can go into remission.
• Treatment-related – The condition may resolve itself sometime after discontinuing the drug(s).

In severe cases involving life-threatening bleeding, blood transfusions may be necessary to replace red blood cells lost from bleeding. Transfusion will not cure the condition but will replace lost red blood cells and may provide enough platelets to slow bleeding.

Prevention

• Use tick preventives year-round to reduce risk of tick-borne infections. However, it is important to note that this condition may develop even if the pet is only taking their prescribed medications according to instructions.
• Keep all medications carefully stored. Pets are curious and may lick or ingest them.
• Seek veterinary care immediately if you notice your pet bruising or bleeding.
• Since thrombocytopenia cannot always be prevented, it is important to always be watchful of your pet and take notice of any changes or signs that may indicate the condition.