Low Blood Platelets (thrombocytopenia) in Cats

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Causes            Symptoms            Diagnosis             Treatment

 

At a glance:

About: Thrombocytopenia is a medical condition in which there is a reduced number of blood platelets, which are responsible for helping the blood to clot. 

Causes: There are a number of causes divided into decreased production, premature destruction, sequestration in the spleen and platelets which are used up faster than they can be produced.

Symptoms: Lethargy, blood in the urine and/or stool, red spots in the eyes, gums, and skin and bruising.

Treatment: Will depend on the underlying cause. In some cases, there will be no treatment at all, severe cases may require a blood transfusion.

 

Platelets

About:

Medically known as thrombocytopenia, low platelets (PLT) is a decreased number of platelets in the blood. Normal platelet levels should be around 200,000 µL (microlitre).

What are platelets?

Platelets (thrombocytes) are disc-shaped, nonnucleated cell fragments which circulate the bloodstream. Their function is to stop blood loss (known as hemostasis). There are three mechanisms which work together, stopping the flow of blood.

  1. Platelet adhesion – When damage to a blood vessel occurs, circulating platelets form a clump over the damaged vessel to block it off.
  2. Coagulation – Fibrinogen is activated by protein factors in the blood-forming fibrin strands. These strands help to mesh the platelet plug, strengthening it.
  3. Vasoconstriction – When a blood vessel becomes damaged, vasoconstriction, making the blood vessel smaller which restricts blood loss from the damaged site.

The bone marrow forms all of the cellular components of the blood. Platelets are produced by cells known as megakaryocytes, these giant cells undergo a process known as fragmentation, releasing platelets into the bloodstream. Platelets circulate in the blood for around seven days before they are destroyed by the macrophages.

Thrombocytopenia can be divided into two types, primary or secondary.

  • Primary or idiopathic thrombocytopenic purpura is where there is no known reason for low platelets.
  • Secondary thrombocytopenia is associated with other illnesses such as cancer, certain drugs or toxins, autoimmune disorders or infection.

Causes:

Causes of low blood platelets (thrombocytopenia) in cats

There are a number of causes of low platelets which can be divided into four main classes: 

  1. Decreased production of platelets
  2. Premature destruction of platelets
  3. Sequestration in the spleen
  4. Platelets are used up faster than they can be produced

Decreased production of platelets

The most common cause of low platelet count in cats causes by diseases which affect production of platelets in the bone marrow. 

Leukemia: A cancer of the blood and bone marrow, as the cancer cells take over the bone marrow, there will be less platelet-producing megakaryocytes.

Myelodysplasia syndrome (bone marrow failure disorders): Stem cells in the bone marrow which is responsible for the production of red and white cells as well as platelets begin producing abnormal cells

Infectious disease: Leptospirosis, feline immunodeficiency virus, feline infectious peritonitis, feline panleukopenia and feline leukemia virus. The feline panleukopenia vaccine may result in a temporary decrease in platelet production.

Idiopathic: Unknown cause.

Premature destruction of the platelets

Autoimmune disorders (immune-mediated thrombocytopenia):  The cat’s own immune system destroys platelets.

Neoplasia: 

  • Lymphoma – Cancer of the lymphatic system.
  • Hemangiosarcoma – A sarcoma arising from the lining of the blood vessels.

Certain drugs: Methimazole, griseofulvin, albendazole, chloramphenicol, propylthiouracil, cytotoxic drugs (carboplatin, azathioprin, doxorubicin).

Sequestration in the spleen 

This organ filters unwanted material from the blood and fights infection and stores up to 30-40% of platelets.  If the spleen becomes enlarged (splenomegaly), it will begin to function abnormally, sequestering a greater number of platelets, up to 90%, and therefore reducing the number of platelets circulating in the blood.

Some forms of cancer can lead to an enlarged spleen. The liver may also sequestrate a number of platelets, however, it’s not at the same level as the spleen.

Platelets are used up quicker than they can be produced

Disseminated intravascular coagulation (DIC): A condition in which systemic activation of clotting occurs, leading to blood clots forming throughout the body, which can cause blockages in the vascular system as well as using up large numbers of platelets to form the clots, major blood loss can also cause a decrease in platelets.

Symptoms:

Many cats with mild thrombocytopenia are often asymptomatic and the condition only comes to light during routine blood work.

As the platelets are there to stop bleeding, one of the obvious symptoms of low platelets is increased bleeding, either from an external wound (cut or a scratch), during surgery, or nosebleeds, bleeding gums, anal bleeding. This may not always be present.

Other common symptoms include:

  • Lethargy
  • Blood in urine
  • Blood in the stool
  • Red spots in the white of the eyes due to retinal hemorrhage
  • Red spots on the gums and skin
  • Purple areas on the skin (bruising)

Other symptoms may vary depending on the underlying cause.

Diagnosis:

Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. Your veterinarian will want to know the following:

  • Any medications your cat is on
  • Exposure to toxins
  • Vaccination history
  • Other symptoms

He will need to run some diagnostic tests to check the platelet count and determine an underlying cause. Some tests may include:

  • Complete blood count – Which will reveal a low platelet count.
  • Prothrombin time – This is a test of the blood coagulation rate.
  • Biochemical profile  – To evaluate organ function.
  • Blood serum test to look for antibodies to Rocky Mountain spotted fever.
  • Urinalysis to check for blood in the urine.
  • Bone marrow aspirate or core biopsy –  A needle extracts a sample of bone marrow from the humerus (upper bone in front leg), femur (thigh bone) or pelvis.  An increase in the number of megakaryocytes suggest increased platelet use, increased platelet destruction or sequestration in the spleen. Decreased megakaryocytes indicate decreased platelet production. Which may be due to cancer or viral infection.
  • X-ray or ultrasound – To check the size and shape of the organs as well as look for tumours. 
  • Biopsy – Of spleen or liver mass.
  • FIV and FeLV blood tests.

Treatment:

Primary thrombocytopenia:

  • Mild cases of thrombocytopenia may require no treatment at all.
  • Corticosteroids to slow down immune mediated platelet destruction.
  • Transfusion of platelets or whole blood.

Secondary thrombocytopenia:

  • The goal is to find and treat the underlying cause.
  • Restrict activity to reduce the risk of injury and/or bleeding for cats with extremely low platelets.
  • Transfusion of platelets or whole blood.

Platelets image courtesy of Zeiss Microscopy, Flickr

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