Rheumatoid Arthritis and Thrombocytosis

Causes and Symptoms of a High Platelet Count

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Activated platelets, artwork
Artist representation of an activated platelet among red blood cells.

Science Photo Library/Sciepro /Getty Images

Platelets, also known as thrombocytes, are blood cells that bind together whenever they encounter a damaged blood vessel and, by doing so, form a clot to prevent bleeding. If you have rheumatoid arthritis (RA), an autoimmune form of arthritis, it is not uncommon to experience an increase in your platelet count. If the increase is excessive, it could lead to a potentially serious condition known as thrombocytosis—when platelets can suddenly and inexplicably form clots in the arms and legs. If left untreated, thrombocytosis can trigger a heart attack or stroke.

Thrombocytosis occurs most frequently in people with severe, untreated RA and should not be confused with thrombocytopenia (low platelets), a condition sometimes caused by RA medications.

Causes

People with RA generally experience secondary thrombocytopenia, meaning that the condition is a consequence of a chronic disease, disorder, or malignancy. By contrast, primary thrombocytosis is a rare blood disorder caused by a group of bone marrow-related diseases known as myeloproliferative neoplasms.

As an autoimmune disease, rheumatoid arthritis is characterized by an immune system gone awry. For reasons poorly understood, the immune system will suddenly attack its own cells and tissues. With RA, the joints are the primary target of the assault, causing direct damage to tissues while spurring chronic and often unrelenting inflammation.

When this happens, certain blood cells, such as erythrocytes (red blood cells), will begin to drop in numbers, sometimes precipitously. By contrast, platelets, which are spurred into action when the body is under attack, will respond differently. The inflammation will instead stimulate a chemical known as platelet-activating factor (PAF) whose role it is to recruit and direct platelets to the site of an injury.

Ultimately, the greater or more persistent the inflammation is, the greater the accumulation of platelets.

Symptoms

Thrombocytosis can often be mild and cause no noticeable symptoms. However, as the platelet volumes increase, symptoms may develop as the abnormal clotting begins to affect blood vessels in the skin, liver, spleen, and other organs.

Common signs and symptoms of thrombocytosis include:

  • Persistent fatigue
  • Easy or excessive bruising
  • Tiny reddish spots (petechiae), usually on the lower legs
  • Prolonged bleeding from cuts
  • Bleeding gums or nose
  • Blood in urine or stools
  • Heavy menstrual flows
  • Pain or fullness in the left upper abdomen (associated with an enlarged spleen)
  • Yellowing of the eyes and possibly the skin (jaundice)

Complications

Within the context of RA, serious complications are typically confined to untreated people over age 65 with known cardiovascular risk or those who have previously experienced bleeding problems. If a clot forms in the brain, it can cause a stroke or a milder transient ischemic attack (TIA or "mini-stroke"). If one forms in the arteries of the heart, it can trigger a myocardial infarction (heart attack).

While serious blockages may occur elsewhere, they are far less common with secondary thrombocytosis than they are with primary thrombocytosis (also known as essential thrombocythemia).

Diagnosis

Thrombocytosis is primarily diagnosed with a complete blood count (CBC). This is a blood test that assesses the overall composition of your blood as well its individual components. This includes the platelet count, which is measured in cubic millimeters (mm3).

By and large, healthy people will have a platelet count of between 150,000 and 400,000/mm3. Thrombocytosis is diagnosed when the count in excess of 400,000/mm3 and is considered serious when it is over 600,000/mm3.

While this can provide definitive evidence of thrombocytosis, your doctor will also perform blood tests known as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to measure the level of generalized inflammation in the body. Liver function tests and renal (kidney) function tests can assess if either of these organ systems has been affected.

Differential Diagnoses

Your doctor may also explore other possible causes if your symptoms are either unusual or excessive. The differential diagnoses may include:

Depending on the suspected cause, the investigation may include a bone marrow biopsy, imaging tests, blood tests, or a blood culture.

Treatment

Thrombocytosis in people with rheumatoid arthritis typically requires no direct treatment. Instead, treatment would be focused on bringing the RA and associated inflammation under control.

Depending on the severity of the disease, this may involve:

Effort should also be made to stop smoking, exercise regularly, and improve your diet, all of which can help lower pain and inflammation.

If the rare instance that thrombocytosis is severe (750,000/mm3 or greater), a daily low-dose aspirin would be prescribed to lower your cardiovascular risk.

Less commonly, oral medications such as hydroxyurea or Agrylin (anagrelide) may be used to help reduce platelet count, generally within four to 12 weeks. Drug side effects are relatively mild but may include nausea, hair loss, discolored nails, and mouth ulcers.

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