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M Glossary



Macrodactyly - a congenital problem in which there is an abnormal growth of a finger or toe.

Macrosomia - a condition in which a baby is considerably larger than normal at birth.

Macula - a small spot inside the eye on the retina that provides the most visual detail.

Macular degeneration - an eye condition in which degeneration in the macular region of the retina results in decreased central vision and, sometimes, blindness.

Macular stains (also called angel's kisses or stork bites) - faint, red marks that appear on the skin at birth. Angel's kisses are marks on the forehead and eyelids. Stork bites are marks on the back of the neck.

Macule - the smaller version of a patch; a flat, discolored spot.

Mad cow disease (Also called bovine spongiform encephalopathy or BSE) - a neurological disease in cattle that is related to a disease in humans called new variant Creutzfeldt-Jakob disease (nvCJD). Both disorders are fatal brain diseases caused by an unconventional transmissible agent.


Major depression (also known as clinical depression or unipolar depression) - a type of affective disorder or mood disorder in which a person's ability to function in normal activities is affected by feelings of sadness, despair, loss, anger, and/or frustration over a long period of time.

Malabsorption syndromes - conditions that may result when the small intestine cannot absorb nutrients from foods.

Malaria - a disease caused by a parasite that is transmitted by the bite of an infected Anopheles mosquito. These mosquitoes are present in the tropics and subtropics in almost all countries. Malaria is the most deadly of all tropical parasitic diseases.

Malignant - cancerous cells are present.

Malignant melanoma - a rare, but sometimes deadly, skin cancer that begins as a mole that turns cancerous.


Malnutrition - condition caused by not eating enough food or not eating a balanced diet.

Malocclusion - an orthodontic problem that means "bad bite," including crowded, missing, or crooked teeth, extra teeth, or a misaligned jaw.

Mammogram - X-ray of the breast tissue.


Manic depression (also known as bipolar disorder) - a type of affective disorder or mood disorder that is characterized by periodic episodes of extreme elation, elevated mood, or irritability (also called mania) countered by periodic, classic depressive symptoms.

Manometry - tests that measure pressure using a device called a manometer. Blood pressure is measured with a sphymomanometer; pressure inside the esophagus or anus can also be measured by manometry.

Mantoux test - a skin test used to identify the presence of tuberculosis infection.

Manual therapy - a type of physical therapy that uses only manual (hands on) techniques.


Mast cell - a type of cell that is involved in inflammatory responses and allergic reactions in the body. When mast cells are stimulated by an allergen, they release histamine and other substances.

Mastalgia - pain in the breast that is generally classified as either cyclical (associated with menstrual periods) or non-cyclical.

Mastectomy - surgical removal of all or part of the breast.

Mastitis - an inflammation of the breast tissue.

Mastoid - back portion of the temporal bone behind the ear.

Mastoid surgery - a type of surgical procedure in which part of the mastoid bone is removed because of infection or other reasons.

Maxillofacial - pertaining to the jaws and face.

Meal plan - a guide to help people include the proper amount of calories, carbohydrates, proteins, fats, vitamins, minerals, and fiber in their diet.

Mean blood pressure - average blood pressure, taking account of the rise and fall that occurs with each heartbeat. It is often estimated by multiplying the diastolic pressure by two, adding the systolic pressure, and then dividing this sum by three.


Meckel's diverticulum - a birth defect in which a small sac that forms in the ileum (lower end of the small intestine) before birth does not resolve by the time the baby is born.


Medial collateral ligament (MCL) - the ligament that gives stability to the inner knee.

Medial epicondylitis (also known as golfer's elbow, baseball elbow, suitcase elbow, or forehand tennis elbow) - pain caused by inflammation of the tendons connected to the muscles that bend the wrist toward the palm.


Medicaid - federally and state-funded health care program for low-income individuals.

Medicare - federally funded health care program for individuals over age 65.

Megacolon - enlarged colon; may be caused by severe constipation. Hirschsprung's disease is a congenital (present at birth) type of megacolon that occurs because of a lack of nerves in parts of the colon.

Megaloblastic (pernicious) anemia - a rare blood disorder in which the body does not absorb enough vitamin B12 from the digestive tract, resulting in an inadequate amount of red blood cells produced.

Meige syndrome - a rare movement disorder that can involve excessive eye blinking (blepharospasm) with involuntary movements of the jaw muscles, lips, and tongue (oromandibular dystonia).

Melanin (also called pigment) - a substance that gives the skin its color.

Melanocytes - cells present in the epidermis that produce melanin (skin pigment).


Melasma - dark, brown, symmetrical patches of pigment on the face.

Melena - blood in the stool.

Menarche - a young woman's first menstrual period.

Ménétrier disease (also called hypoproteinemic hypertrophic gastropathy) - a condition in which the ridges inside the stomach, called ruguae, become enlarged and cause too much mucus to collect in the stomach. The stomach also absorbs protein from the blood, causing too little protein in the blood. There is also a decrease in acid production in the stomach.





Menorrhagia (also called dysfunctional uterine bleeding) - the most common type of abnormal uterine bleeding characterized by heavy and prolonged menstrual bleeding. In some cases, bleeding may be so severe and relentless that daily activities become interrupted.

Menses - menstrual flow.


Mercury poisoning - an abnormal condition caused by breathing or swallowing a mercury substance.


Metaplasia - the phenomenon by which one type of tissue is replaced by another type.



Methyl-tert-butyl ether (MTBE) - a solution injected into the gallbladder to dissolve gallstones. Use of MTBE for this purpose remains investigational and is not done widely. 

Metrorrhagia - any irregular, acyclic, non-menstrual bleeding from the uterus; bleeding between menstrual periods.

Micrographia - a change in handwriting with the script becoming smaller and more cramped.

Microsurgical fertilization - a procedure used to facilitate sperm penetration into the oocyte, and fertilization takes place under the microscope.


Milia - tiny, white, hard spots that look like pimples on a newborn's nose. Adults may also have milia on the face. 


Miosis - constriction of the pupil.

Misarticulation - inaccurately produced speech sound (phoneme) or sounds.




Mobility - movement.

Modified radical mastectomy - the removal of the entire breast (including the nipple, areola, and overlying skin), some of the lymph nodes under the arm (also called the axillary lymph glands), and the lining over the chest muscles. In some cases, part of the chest wall muscles is also removed.

Mold - a microscopic fungus that grows and lives on plant or animal matter or on non-organic objects. Most molds are made up of filaments and reproduce through the production of spores, which spread by air, water, or insects.

Moles - small skin marks caused by pigment-producing cells in the skin.

Mongolian spots - bluish-black marks on the lower back and buttocks; affects mainly African-American or Asian children. The spots appear at birth or soon after, and generally disappear without treatment within a few years. 





Morton's neuroma - a condition in which the nerve tissue between the toes, usually the third and fourth toes, becomes thickened, causing pain in the ball of the foot, as well as tingling, burning, and cramping between the toes.

Motility - movement of food through the digestive tract.


Motor speech disorders - group of speech disorders caused by the inability to accurately produce speech sounds (phonemes), because of weakness or lack of coordination of involved muscles.


Moxibustion - the burning of herbal leaves on or near the body.

Mucosal lining - lining of gastrointestinal (GI) tract organs that makes mucus.

Mucosal protective drugs - medications that protect the stomach lining from acid.

Mucus - a thick, jelly-like substance made by the intestines and other organs of the body (such as the nose), that helps coat and protect the lining of the organ. Mucus also helps stool pass through the large intestine and rectum more easily.

Multifidus - deep lumbar spine muscle that stabilizes the lumbar spine.

Multiple chemical sensitivity - a diagnostic label for people who suffer multi-system illnesses as a result of contact with, or proximity to, a variety of airborne agents and other substances.

Multiple sclerosis (MS) - an autoimmune disease that affects the brain and spinal cord by damaging the sheath surrounding nerve cells. MS can be relatively benign, disabling, or devastating, leaving the patient unable to speak, walk, or write.

Multiple semen analysis - a test to evaluate a man's sperm in which at least two semen examples are collected on separate days to examine the semen and sperm for various factors, such as semen volume, consistency, and pH, and the sperm count, motility, and morphology (shape).



Muscular dystrophy (MD) - a broad term that describes a group of genetic (inherited) disorder of the muscles. MD causes the muscles in the body to become very weak. The muscles break down and are replaced with fatty deposits over time. The most common form of MD is called Duchenne muscular dystrophy (DMD).



Mycosis fungoides - cutaneous T-cell lymphoma skin tumors.

Mydriasis - dilation of the pupil.

Myelogenous leukemia - a type of leukemia in which the cancer develops in the granulocytes or monocytes (myeloid cells).


Myeloproliferative disorders - diseases in which the bone marrow produces too many of one of the three types of blood cells: red blood cells, which carry oxygen to all the tissues in the body; white blood cells, which fight infection; and platelets, which control bleeding.

Myocardial infarction (also called heart attack) - occurs when one of more regions of the heart muscle experience a severe or prolonged decrease in oxygen supply caused by a blocked blood flow to the heart muscle.

Myocardial ischemia - insufficient blood flow to part of the heart.

Myocardium - the muscle wall of the heart.

Myoclonus - jerking, involuntary movements of the arms and legs; may occur normally during sleep.

Myofascial pain - the most common form of temporomandibular disorder; discomfort or pain in the muscles that control jaw function and the neck and shoulder muscles.

Myomectomy - surgical procedure done to remove fibroids from the uterus while leaving the uterus intact.

Myopia - nearsightedness.
