Diagnosis of Hairy Cell Leukemia

Patients with hairy cell leukemia may develop many different symptoms. A physician should use careful clinical judgement to accurately diagnose a patient’s disease.

In some patients with hairy cell leukemia, the doctor can feel an enlarged spleen on physical examination. The spleen is located in the upper left side of the abdomen and when it is particularly large it may cause symptoms such as early fullness during a meal.

In the original series published by Dr. Bertha Bouroncle, an enlarged spleen was found in more than 90% of patients with hairy cell leukemia. However, the finding of an enlarged spleen has become less common over the years due to the more frequent use of blood tests to diagnose hairy cell leukemia. Patients now will commonly have low blood counts (hemoglobin, neutrophils and monocytes) in the absence of any symptoms. Thrombocytopenia is also very common. Therefore, the failure to identify an enlarged spleen does not preclude the diagnosis of hairy cell leukemia.

To find the cause of an enlarged spleen or the reason for an abnormal blood test, more investigations will need to be done, generally by a hematologist. It may be necessary for the hematologist to order a full blood count (test that measures many features and components of the blood) and other blood tests such as a peripheral blood smear (test used to look for abnormalities in blood cells), immunophenotyping (process that uses antibodies to identify cells based on the markers on the surface of the cells), a bone marrow biopsy, and imaging tests like an ultrasound or a CAT scan of the abdomen.

The full blood count test will often show anemia (low red blood cell count that can predispose to fatigue), low white blood cell count (that can predispose to infection), and a low platelet count (that can predispose to bleeding).

The peripheral blood smear will often show a reduction or absence of a type of white blood cells called monocytes, and may document the appearance of cells with a pale cytoplasm with a “hairy” rim. These leukemic cells have a distinct appearance under the microscope. If they are not seen, this does not exclude a diagnosis of hairy cell leukemia, as the hairy cells may be found in the bone marrow only.

Immunophenotyping is a test that helps identify the hairy cells with the use of markers (so called ‘clusters of differentiation’ or CD) by ‘monoclonal antibodies’, each of which has a number or a name and will be expressed on all the malignant cells. The characteristic immunophenotype shows positivity of the leukemic cells for CD19, CD20, CD11c, CD25, CD103, CD123. Their co-expression on the hairy cells confirms the diagnostic features of  “classic HCL”. There are other markers such as CD200 that are also positive.

In the variant form of HCL, the leukemic cells are negative for CD25 and CD123 and the leukemic cell count in the peripheral blood is generally high.

The absolute numbers of these leukemic cells can be useful in establishing the diagnosis and determining when treatment should be initiated.

A bone marrow biopsy is performed by using a needle to take a sample of bone near the rear area of the hip. While this can be painful, the physician can give both local and other medication to reduce the pain. This procedure is relatively quick, and provides a very useful confirmation of the diagnosis. The bone marrow biopsy consists of two separate assessments. The first assessment is called bone marrow aspirate. This test will allow the hematologist to find hairy cells in the bone marrow on a smear and by immunophenotyping like in the peripheral blood. The other test is called bone marrow trephine. This type of biopsy will be reviewed by a specialized pathologist who will look at the architecture of the bone marrow and other characteristics of the hairy cells to complete the diagnosis.

An accurate diagnosis is necessary to determine the correct treatment for each patient. It may be helpful to seek consultation at a Center of Excellence.