Myel Health Dictionary

  1. Health Encyclopedia
  2. Myel

Myel: From 1 Different Sources

Myelin

A substance made up of protein and phospholipid that forms the sheath surrounding the axons of some neurons (see NEURON(E)). These are described as myelinated or medullated nerve ?bres, and electric impulses pass along them faster than along non-myelinated nerves. Myelin is produced by Schwann cells which occur at intervals along the nerve ?bre. (See MULTIPLE SCLEROSIS (MS).)... myelin

Myelitis

Myelitis is in?ammation of the SPINAL CORD.... myelitis

Myelography

The injection of a radio-opaque substance into the central canal of the SPINAL CORD in order to assist in the diagnosis of diseases of the spinal cord or spine using X-ray examination. Because of the high risk of causing damage to the spinal cord (arachnoiditis), it has been largely superceded by MRI.... myelography

Myeloma

See MYELOMATOSIS.... myeloma

Myelomatosis

A MALIGNANT disorder of PLASMA cells, derived from B-lymphocytes (see LYMPHOCYTE). In most patients the BONE MARROW is heavily in?ltrated with atypical, monoclonal plasma cells, which gradually replace the normal cell lines, inducing ANAEMIA, LEUCOPENIA, and THROMBOCYTOPENIA. Bone absorption occurs, producing di?use osteoporosis (see under BONE, DISORDERS OF). In some cases only part of the immunoglobulin molecule is produced by the tumour cells, appearing in the urine as Bence Jones PROTEINURIA.

The disease is rare under the age of 30, frequency increasing with age to peak between 60 and 70 years. There may be a long preclinical phase, sometimes as long as 25 years. When symptoms do occur, they tend to re?ect bone involvement, reduced immune function, renal failure, anaemia or hyperviscosity of the blood. Vertebral collapse is common, with nerve root pressure and reduced stature. The disease is eventually fatal, infection being a common cause of death. Local skeletal problems should be treated with RADIOTHERAPY, and the general disease with CHEMOTHERAPY

– chie?y the ALKYLATING AGENTS melphalan or cyclophosphamide. Red-blood-cell TRANSFUSION is usually required, together with plasmapheresis (see PLASMA EXCHANGE), and orthopaedic surgery may be necessary following fractures.... myelomatosis

Myeloblast

Present in the blood-producing tissue in the BONE MARROW, this is a cell with a large nucleus and scanty cytoplasm. It is the precursor cell of a granulocyte (see GRANULOCYTES). Myeloblasts sometimes appear in the blood of patients with various diseases including acute myeloblastic LEUKAEMIA.... myeloblast

Myelocyte

The name given to one of the cells of BONE MARROW from which the granular white cells of the blood are produced. They are found in the blood in certain forms of LEUKAEMIA.... myelocyte

Myeloid

An adjective that relates to the granulocyte (see GRANULOCYTES) precursor cell in the BONE MARROW. For example, myeloid LEUKAEMIA, which arises from abnormal growth in the blood-forming tissue of the bone marrow.... myeloid

Myelosuppression

A fall in the production of blood cells in the BONE MARROW. This fall often occurs after CHEMOTHERAPY for cancer. ANAEMIA, infection and abnormal bleeding are symptomatic of myelosuppression.... myelosuppression

Myelocele

Another name for myelomeningocele (see neural tube defect).... myelocele

Myelofibrosis

An alternative term for myelosclerosis.... myelofibrosis

Myelomeningocele

A protrusion of the spinal cord and its meninges (protective membranes) under the skin due to a congenital defect (see neural tube defect).... myelomeningocele

Leukaemia, Chronic Myeloid

A type of leukaemia, also called chronic granulocytic leukaemia, which is caused by the overproduction of granulocytes, neutrophils, or polymorphonuclear leukocytes (see blood cells). The cause is unknown. This type of leukaemia usually has 2 phases: a chronic phase, which may last for several years, and a more cancerous phase, which is known as the blastic, accelerated, or acute phase.

During the chronic phase, symptoms may include fever, night sweats, and weight loss. Visual disturbances, abdominal pain, and priapism may also occur. The symptoms of the more cancerous phase are like those of the acute forms of leukaemia (see leukaemia, acute). The diagnosis is made from blood tests and a bone marrow biopsy. Treatment of the chronic phase includes anticancer drugs. When the disease transforms into the acute phase, treatment is similar to that given for acute leukaemia.... leukaemia, chronic myeloid

Myeloma, Multiple

See multiple myeloma.... myeloma, multiple

Myelopathy

Any disease or disorder of the spinal cord.... myelopathy

Central Pontine Myelinolysis

acute paralysis, dysphagia, and dysarthria resulting from damage to the myelin sheaths of nerve cells in the brainstem. It occurs most commonly as a complication of rapid correction of severe hyponatraemia (low serum sodium).... central pontine myelinolysis

Myelencephalon

n. see medulla oblongata.... myelencephalon

Myelination

n. the process in which *myelin is laid down as an insulating layer around the axons of certain nerves. Myelination of nerve tracts in the central nervous system is completed by the second year of life.... myelination

Myelodysplastic Syndromes

(MDS) a group of diseases in which the production of any one or all types of blood cells by the bone marrow is disrupted. Although myelodysplastic syndromes were previously referred to as preleukaemia, only a minority of patients with myelodysplastic syndromes develop leukaemia.... myelodysplastic syndromes

Multiple Myeloma

Also called myelomatosis, multiple myeloma is a rare, cancerous condition in which plasma cells in the bone marrow proliferate uncontrollably and function incorrectly. It occurs in middle- to old age.

Plasma cells are a type of B-lymphocyte that produce immunoglobulins, which help protect against infection. In multiple myeloma, the proliferating plasma cells produce excessive amounts of one type of immunoglobulin, while production of other types is impaired. This makes infection more likely.Proliferation of the abnormal cells causes pain and destroys bone tissue.

Affected vertebrae may collapse and compress nerves, causing numbness or paralysis. Blood calcium levels increase as bone is destroyed, as may the level of one or more immunoglobulins. These changes in the blood may damage the kidneys, leading to kidney failure. There may also be anaemia and a tendency for abnormal bleeding.

The disease is diagnosed by a bone marrow biopsy, by blood tests or urinalysis, and by X-rays. Treatment includes the use of anticancer drugs, radiotherapy, and supportive measures, including blood transfusions, antibiotic drugs, and analgesic drugs.... multiple myeloma

Myelosclerosis

An increase of fibrous tissue within the bone marrow (also known as myelofibrosis), in which the marrow’s ability to produce blood cells is impaired. Myelosclerosis may be primary (occurring with no obvious cause) or secondary (resulting from another bone marrow disease).

The main symptoms of myelosclerosis are those of anaemia. Enlargement of the spleen, night sweats, loss of appetite, and weight loss also commonly occur. In secondary myelosclerosis, the underlying disease may cause other symptoms. Treatment of primary myelosclerosis includes blood transfusions to relieve symptoms. A few patients may develop acute leukaemia. Treatment of secondary myelosclerosis depends on the underlying cause.... myelosclerosis

Myeloid Leukaemia

a variety of *leukaemia in which the type of blood cell that proliferates abnormally originates in the blood-forming (myeloid) tissue of the bone marrow. Myeloid leukaemias may be acute or chronic and may involve any one of the cells produced by the marrow. Blood cells in patients with chronic myeloid leukaemia contain a reciprocal *translocation between chromosomes 9 and 22 (see Philadelphia chromosome); molecular characterization of the translocation has led to the development of specific drugs to block the effects of this abnormality (see tyrosine kinase inhibitor).... myeloid leukaemia

Myeloid Tissue

a tissue in the *bone marrow in which the various classes of blood cells are produced. See also haemopoiesis.... myeloid tissue

Myeloma Kidney

see cast nephropathy.... myeloma kidney

Myelomalacia

n. softening of the tissues of the spinal cord, most often caused by an impaired blood supply.... myelomalacia

Myeloproliferative Disorders

(MPD) a group of diseases in which there is excessive production of blood cells in the bone marrow. Myeloproliferative disorders include *polycythaemia vera, essential *thrombocythaemia, idiopathic *myelofibrosis, and chronic *myeloid leukaemia.... myeloproliferative disorders

Health encyclopedia icon Health Encyclopedia

Recent Searches