Dictionary

histiocytosis X See Langerhans cell histiocytosis.

histiocytosis, sinus A type of histiocytosis in which the lymph nodes are the main site of histiocyte proliferation. The sinuses of the lymph nodes become filled with and distended by masses of histiocytes.

histiocytosis, lipid See Niemann-Pick disease.

histiocytosis, Langerhans cell See Langerhans cell histiocytosis.

histiocytosis One of several disorders in which histiocytes start to multiply and proliferate abnormally. The result can be tissue damage, pain, the development of tumor-like lumps, fatigue, and other symptoms. If histiocytosis affects the pituitary gland, diabetes insipidus may also develop. Treatment includes radiation and chemotherapy, although for reasons unknown, some cases of histiocytosis go…

histiocyte A type of white blood cell, also called a macrophage, that is created by bone marrow. Histiocytes usually stay in place, but when they are stimulated by infection or inflammation, they become active, attacking bacteria and other foreign matter in the body. See also histiocytosis.

histamine cephalalgia See cluster headache.

histamine A substance that plays a major role in many allergic reactions, dilating blood vessels and making the vessel walls abnormally permeable. Histamine is part of the body’s natural allergic response to substances such as pollens. Antihistamines work by preventing the release of histamine from certain cells (mast cells) thereby blocking the allergic reaction.

His disease See trench fever.

hirudin An anticlotting agent that prevents blood clots from traveling through the bloodstream to clog up a vessel (thromboembolic complications). Hirudin is the main chemical in the secretion of leeches that allows them to suck out blood freely from the body after they attach to the skin. Desirudin and lepirudin (brand name: Refludan) are genetically…

hirsutism Having excessive facial and bodily hair. Hirsutism can be a side effect of certain medications (such as prednisone) or reflect an underlying hormonal imbalance.

hirsute Having an overabundance of hair.