Hairy cell leukemia is a lymphoid leukemia that most commonly affects the bone marrow and spleen. However, because HCL travels between the bone marrow, spleen, liver, and lymph nodes via the bloodstream, HCL may potentially affect any part of the body that the blood circulates to. Therefore, other medical problems have been described that are likely a direct or indirect result of the HCL. This section will provide a brief review of both the common and uncommon complications of HCL.

When HCL is present in the bone marrow, over time it slowly proliferates until eventually it begins to prevent normal blood cell production. This leads to lowering of the normal blood counts and may be manifested as low red cell counts (anemia), low platelet counts (thrombocytopenia), and/or lower than normal white blood cells (neutropenia, lymphocytopenia, and monocytopenia). Many of the symptoms and complications of HCL are a direct result of low blood cell counts. In addition, in some patients HCL will begin to circulate in the blood stream and when this happens the white blood count may actually be higher than normal. Therefore, while it is true that some patients with HCL have an elevated white blood cell count due to the presence of hairy cells in the bloodstream, these are not normally functioning white blood cells and do not protect against infection. Whether the white blood count his high or low, patients with HCL are overall at increased risk of infection and in fact infection is one of the leading causes of illness and death for patients with HCL. Infections can be caused by bacteria, viruses, or fungal diseases. In addition, some medications used to treat HCL can temporarily increase the risk of infection by decreasing the white blood cell numbers or normal functioning. For example, the chemotherapy agents most commonly used for the initial treatment of HCL, pentostatin and cladribine, can lower the number of normal lymphocytes. This side effect of therapy can last for many months, and increase the risk of developing a viral disease (e.g., herpes zoster or shingles) or fungal diseases that can cause pneumonia. Patients with HCL should not receive the herpes zoster vaccine from their physicians, as it is a live virus vaccine that might result in causing the condition that it is intended to prevent. However, immunizations using killed virus vaccines, such as the influenza vaccine, are safe and may provide important protection for HCL patients. Prompt attention to fever and symptoms related to infection are a key component of the successful management of this potential complication.

Lowering of the red blood cell count, or anemia, is often associated with symptoms of fatigue. Some patients will require a red blood cell transfusion to correct this problem, although this is a temporary solution until the HCL improves. Lowering of the platelet counts lead to an increased tendency to bleed, and many patients with low platelet counts notice an increased tendency to develop bruising, or bleeding from the gums or nose. If bleeding is severe or the platelet count is very low, a platelet transfusion may be required. However, again this is a temporary solution until treatment is given to improve the underlying HCL.

In the past, significant enlargement of the spleen was a very common complication of HCL and was often the initial symptom of the disease. Although patients today are more often diagnosed with HCL on the basis of an abnormal blood count, many patients will still develop an enlarged spleen as part of the disease course. This may cause symptoms of abdominal pain, abdominal distention, or difficulty eating a full meal due to the pressure that the enlarged spleen exerts on the stomach. Most of the effective therapies for HCL will decrease the size of the spleen, relieving these discomforts. It is possible to remove the spleen if need be, although this will lead to an increased risks of certain types of infection as is usually only performed if other therapies are not possible or have not proven effective. In addition, when the spleen is very enlarged there is an increased risk of splenic rupture due to trauma, such as a car accident. Sudden pain in the abdomen followed by profound weakness should result in seeking immediate medical care in an emergency facility.

There has been some concern that the therapy for hairy cell leukemia may increase the patient’s risk for developing another secondary cancer. This is an ongoing issue of debate. Some studies show that the disease itself may actually increase this risk. Therefore, people with HCL should continue to have their routine cancer screening performed at regular intervals based upon recommendations established by cancer experts.

Further defining the more rare complications of HCL is an ongoing research initiative. For example, there is some suggestion that certain types of autoimmune complications many manifest in patients with HCL, such as certain types of arthritis and immune-mediated blood disorders. Understanding the complications of HCL is one of the main goals of the HCL Patient Data Registry, and the valuable insights gained by this project will add to the understanding of this rare disease.