DEFINITION Marfan syndrome is an inherited disorder that affects connective tissue — the fibers that support and anchor your organs and other structures in your body. Marfan syndrome most commonly affects the heart, eyes, blood vessels and skeleton. People with…
DEFINITION Mammary duct ectasia (ek-TAY-zhuh) occurs when a milk duct beneath your nipple widens, the duct walls thicken and the duct fills with fluid. The milk duct may become blocked or clogged with a thick, sticky substance. The condition often…
DEFINITION Menorrhagia is the medical term for menstrual periods with abnormally heavy or prolonged bleeding. Although heavy menstrual bleeding is a common concern among premenopausal women, most women don’t experience blood loss severe enough to be defined as menorrhagia. With…
DEFINITION Mental illness refers to a wide range of mental health conditions — disorders that affect your mood, thinking and behavior. Examples of mental illness include depression, anxiety disorders, schizophrenia, eating disorders and addictive behaviors. Many people have mental health…
DEFINITION Microcephaly (my-kroh-SEF-uh-lee) is a rare neurological condition in which an infant’s head is significantly smaller than the heads of other children of the same age and sex. Sometimes detected at birth, microcephaly usually is the result of the brain…
DEFINITION In metachromatic leukodystrophy, a rare hereditary (genetic) disorder, deficiency of an enzyme that helps break down fatty substances (lipids) causes lipids to build up in your brain, spinal cord and peripheral nerves. As a result, your brain and nervous…
DEFINITION Metabolic syndrome is a cluster of conditions — increased blood pressure, a high blood sugar level, excess body fat around the waist and abnormal cholesterol levels — that occur together, increasing your risk of heart disease, stroke and diabetes.…
DEFINITION Malignant mesothelioma (me-zoe-thee-lee-O-muh) is a rare cancer that occurs in the thin layer of tissue that covers the majority of your internal organs (mesothelium). Mesothelioma is an aggressive and deadly form of cancer. Mesothelioma treatments are available, but for…
DEFINITION Lymphadenitis is a condition in which your lymph nodes — tissues that help your body fight off illness — become inflamed. Mesenteric lymphadenitis (mez-un-TER-ik lim-fad-uh-NIE-tis) is an inflammation of the lymph nodes in the membrane that attaches your intestine…
DEFINITION Mesenteric ischemia (mez-un-TER-ik is-KEE-me-uh) is a condition caused by poor blood supply to your intestines. Mesenteric ischemia usually affects the small intestine, colon or both. It may also involve other organs in the digestive system. Mesenteric ischemia may be…
DEFINITION Merkel cell carcinoma is a rare type of skin cancer that usually appears as a flesh-colored or bluish-red nodule, often on your face, head or neck. Merkel cell carcinoma is also called neuroendocrine carcinoma of the skin. Merkel cell…
DEFINITION Meralgia paresthetica is a condition characterized by tingling, numbness and burning pain in your outer thigh. The cause of meralgia paresthetica is compression of the nerve that supplies sensation to the skin surface of your thigh. Tight clothing, obesity…