Malignant histiocytosis
Malignant histiocytosis (also known as "Histiocytic medullary reticulosis") is a rare hereditary disease found in the Bernese Mountain Dog and humans, characterized by histiocytic infiltration of the lungs and lymph nodes. The liver, spleen, and central nervous system can also be affected. Histiocytes are a component of the immune system that proliferate abnormally in this disease. In addition to its importance in veterinary medicine, the condition is also important in human pathology.
Histiocytic disorders
A histiocyte is a differentiated tissue cell that has its origin in the bone marrow. The source for histiocytes is the monocyte/macrophage line. Monocytes (found in the blood) and macrophages (found in tissue) are responsible for phagocytosis (ingestion) of foreign material in the body. Langerhans cells are dendritic cells found in the skin and function by internalizing antigens (foreign particles) and presenting them to T cells. They arise from monocytes. Histiocytic disorders refer to diseases that are caused by abnormal behavior of these cells. They include the following:
Histiocytosis
In medicine, histiocytosis refers to an excessive number of histiocytes, (tissue macrophages), and is typically used to refer to a group of rare diseases which share this as a characteristic. Occasionally and confusingly, the term "histiocytosis" is sometimes used to refer to individual diseases.
According to the Histiocytosis Association of America, 1 in 200,000 children in the United States are born with histiocytosis each year. HAA also states that most of the people diagnosed with histiocytosis are children under the age of 10, although the disease can afflict adults. The University of California, San Francisco, states that the disease usually occurs from birth to age 15.
Histiocytosis (and malignant histiocytosis) are both important in veterinary as well as human pathology.
Classification, and relationships to other conditions
There are competing systems for classifying histiocytoses. According to the 1999 classification proposed by the World Health Organization, they can be divided into three categories. However, the classifications in ICD10 and MeSH are slightly different, as shown below:
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