Dictionary

myeloencephalitis See encephalomyelitis.

myelodysplastic syndrome One of a group of disorders characterized by abnormal development of one or more of the cell lines that are normally found in the bone marrow. Patients can develop a variety of symptoms related to anemia, low or high white blood cell count, infections, and bleeding problems. Myelodysplastic syndrome may progress and become…

myelitis Inflammation of the spinal cord, such as from infection or immune inflammation.

myelination The formation of the myelin sheath around a nerve fiber. Also known as myelinization. See also myelin.

myelin The fatty substance that covers and protects nerves. Myelin is a layered tissue that surrounds the nerve fibers (axons). This sheath around the axons acts like a conduit in an electrical system, ensuring that messages sent by axons are not lost en route.

mydriasis Dilation of the pupil. The opposite of mydriasis is miosis.

mycosis fungoides A type of non-Hodgkin’s lymphoma that first appears on the skin. Also known as cutaneous T-cell lymphoma.

mycoplasma pneumoniae A mycoplasma that can infect the upper respiratory tract and the lungs. Mycoplasma pneumoniae is a major cause of respiratory infection in children of school age and young adults. It is also a common cause of pneumonia in persons with HIV. Treatment involves use of antibiotics, including tetracycline and erythromycin.

mycoplasma hominis A common inhabitant of the vagina that can cause infections of the female and male genital tracts. Treatment involves use of antibiotics, including tetracycline and erythromycin.

mycoplasma A large group of bacteria, with more than 100 types identified. Mycoplasma are very simple one-celled organisms without outer membranes. They penetrate and infect individual cells. Mycoplasma hominis and Mycoplasma pneumoniae are examples of mycoplasma bacteria that occur in humans.

mycobacterium avium complex A serious opportunistic infection that is caused by two similar bacteria, Mycobacterium avium and Mycobacterium intercellulare, which are found in the soil and in dust particles. Abbreviated MAC. In persons with suppressed immune systems, such as people with AIDS, MAC can spread through the bloodstream to infect lymph nodes, bone marrow, the…

myasthenia gravis An autoimmune neuromuscular disorder that is characterized by fatigue and exhaustion of muscles. Abbreviated MG. MG is caused by a mistaken immune response to the body’s own nicotinic acetylcholine receptors, which are found in junctions between muscles and the nervous system. The body produces antibodies that attack these receptors, preventing signals from reaching…