Hemophagocytic Lymphohistiocytosis

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Hemophagocytic Lymphohistiocytosis
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Specialty scores for Hemophagocytic Lymphohistiocytosis

Overview

Familial hemophagocytic lymphohistiocytosis is a rare, immune mediated disorder in which the immune system produces too many activated lymphocytes called T cells, natural killer cells, B cells, macrophages (histiocytes) and cytokines. Overactivation of the immune system leads to fever, constitutional symptoms and damages the liver and spleen, resulting in hepatomegaly and splenomegaly. Familial hemophagocytic lymphohistiocytosis also leads to destruction of blood-producing cells in the bone marrow, by the process of hemophagocytosis. Due to this, affected patients suffer with anemia (low numbers of red blood cells) and thrombocytopenia (a reduction in the number of platelets), which are involved in clotting. Familial hemophagocytic lymphohistiocytosis affects approximately 1 in 50,000 individuals worldwide.

Causes:

Familial hemophagocytic lymphohistiocytosis may be caused by genetic mutations. These genes encode proteins that help destroy or deactivate lymphocytes that are no longer required. Approximately 40-60% percent of cases of familial hemophagocytic lymphohistiocytosis are caused by genetic mutations in the PRF1 or UNC13D genes. Smaller numbers of cases are due to mutations in other genes. In some patients, the genetic cause of the disorder is unknown.

Signs and symptoms:

Signs and symptoms of familial hemophagocytic lymphohistiocytosis usually appear during infancy, although they may appear later in life. Clinical features usually become apparent when the immune system gives rise to an exaggerated response to an infection. The signs and symptoms can appear in the absence of infection as well. Thrombocytopenia may cause easy bruising and abnormal bleeding. Anemia usually leads to fatigue, shortness of breath, paleness and weakness. Other signs and symptoms include fever, hepatomegaly (enlarged liver), splenomegaly (enlarged spleen), skin rash, lymphadenopathy, chills, loss of appetite and weight loss.

Brain may be involved in the patients giving rise to the signs and symptoms of irritability, delayed closure of the bones of the skull in infants, impaired muscle coordination, neck stiffness, abnormal muscle tone, blindness, seizures, paralysis, and coma. In addition to neurological problems, abnormalities of the heart, kidneys, and other organs and tissues may occur. Affected individuals also bear increased risk of developing leukemia and lymphoma. Without treatment, most people survive only a few months.

Diagnosis:

The diagnosis requires high index of disease suspicion and warrants medical history, clinical examination, imaging studies, clinical blood tests and genetic tests.

Management:

Therapeutic goal usually involves achievement of clinical stability and then to cure the disease with bone marrow transplantation. During the initial doses of dexamethasone, antimycotic prophylaxis is used. Sulfamethoxazole and trimethoprim is administered as prophylaxis for Pneumocystis carinii because of immune suppression. Intravenous immunoglobulin may be effective in suppressing symptoms when administered soon after disease onset. High-risk patients may receive the etoposide (ie, VP-16) regimens, while the patients who are at low risk may be treated with only cyclosporine, corticosteroids, or intravenous immunoglobulins (IVIG). Bone marrow transplant is performed when the patient is stable. In case of uncontrolled hypersplenism or life-threatening respiratory difficulty, splenectomy may be performed.