Hairy cell leukemia overview

# Overview
Hairy cell leukemia arises from  B cells, that are normally involved in the process of human immunoglobulins production. However, the exact B cell maturation stage involved in the development of hairy cell leukemia is still unclear. The most common gene involved in the pathogenesis of hairy cell leukemia is a BRAF V600E mutation. On microscopic histopathological analysis, characteristic findings of hairy cell leukemia include small cells with "fried egg"-like appearance, well-demarcated thread-like cytoplasmic extensions, and a clear cytoplasm. Hairy cell leukemia is found to approximately comprise 2% of all leukemias in the United States. The incidence of hairy cell leukemia is approximately 3.2 per 1,000,000 individuals in the United States. The incidence of hairy cell leukemia increases with age; the median age at diagnosis is 58 years. Males are more commonly affected with hairy cell leukemia than females. The male to female ratio is approximately 4 to 1. Studies have proposed a number of risk factors for the development of hairy cell leukemia such as certain chemicals exposure, radiation exposure, and sawdust exposure. Symptoms of hairy cell leukemia include fever, night sweats, and weight loss.  Physical examination of patients with hairy cell leukemia is usually remarkable for pallor, petechiae, and splenomegaly. Laboratory findings consistent with the diagnosis of hairy cell leukemia include abnormal complete blood count, immunohistochemistry, and flow cytometry. The presence of hairy cells with thread-like cytoplasmic extensions on blood smear is a key diagnostic feature among patients with hairy cell leukemia. There are no curative treatments for hairy cell leukemia. The mainstay of therapy for hairy cell leukemia patients is chemotherapy. Pharmacological agents used for the treatment of hairy cell leukemia patients include cladribine, pentostatin, rituximab, and vemurafenib.

# Historical Perspective
The term hairy cell leukemia was first used to describe the malignancy by Dr. R. Schrek and Dr. W. J. Donnelly, in 1966.

# Classification
Hairy cell leukemia may be classified into two sub-types which include hairy cell leukemia (classic) and hairy cell leukemia (variant).

# Pathogenesis
Hairy cell leukemia arises from  B cells, that are normally involved in the process of human immunoglobulins production. However, the exact B cell maturation stage involved in the development of hairy cell leukemia is still unclear. The most common gene involved in the pathogenesis of hairy cell leukemia is BRAF V600E mutation. On microscopic histopathological analysis, characteristic findings of hairy cell leukemia include small cells with "fried egg"-like appearance, well-demarcated thread-like cytoplasmic extensions, and a clear cytoplasm.

# Causes
There are no established direct causes for hairy cell leukemia. Common genetic mutations involved in the development of hairy cell leukemia.

# Epidemiology and Demographics
Hairy cell leukemia is found to approximately comprise 2% of all leukemias in the United States. The incidence of hairy cell leukemia is approximately 3.2 per 1,000,000 individuals in the United States. The incidence of hairy cell leukemia increases with age; the median age at diagnosis is 58 years. Males are more commonly affected with hairy cell leukemia than females. The male to female ratio is approximately 4 to 1.

# Risk Factors
Studies have proposed a number of risk factors for the development of hairy cell leukemia such as certain chemicals exposure, radiation exposure, and sawdust exposure.

# Screening
According to the the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for hairy cell leukemia.

# Natural History
Most patients with hairy cell leukemia are asymptomatic at the time of diagnosis. If left untreated, most of the patients with hairy cell leukemia will gradually develop anemia, recurrent infections, and recurrent bleeding. The complications of hairy cell leukemia are mainly due to bone marrow failure.

# Diagnosis

## Staging
There is no established system for the staging of hairy cell leukemia.

## History and Symptoms
Symptoms of hairy cell leukemia include fever, night sweats, and weight loss.

## Physical Examination
Physical examination of patients with hairy cell leukemia is usually remarkable for pallor, petechiae, and splenomegaly.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of hairy cell leukemia include abnormal complete blood count, immunohistochemistry, and flow cytometry. The presence of hairy cells with thread-like cytoplasmic extensions on blood smear is a key diagnostic feature among patients with hairy cell leukemia.

## CT Scan
Abdominal CT scan may be helpful in the diagnosis of hairy cell leukemia. The presence of splenomegaly on CT scan is suggestive of hairy cell leukemia.

## MRI
MRI of the femur may be helpful in the diagnosis of hairy cell leukemia. Diffuse hyper-intense lesions on T2-weighted MRI image is suggestive of bone marrow infiltration by malignant leukemic cells.

# Medical Therapy
There are no curative treatments for hairy cell leukemia. The mainstay of therapy for hairy cell leukemia patients is chemotherapy. Pharmacological agents used for the treatment of hairy cell leukemia patients include cladribine, pentostatin, rituximab, and vemurafenib.

# Surgery
The predominant therapy for hairy cell leukemia is chemotherapy. Surgical management, such as splenectomy, may be required in certain cases.