Online Medical Dictionary

Letter M

M.D.: Abbreviation for medical doctor.
Macro-: Prefix defining large or large-scale.
Macrovascular Disease: Disease of the macro blood vessels, sometimes induced by long-term diabetes. This includes disease of the coronary arteries or aorta, brain arteries (cerebrovascular), and arteries located in the limbs (peripheral vascular).
Macula: A small, yellow spot located centrally in the retina of the eye, key in providing central, or high acuity, vision.
Macular Degeneration: A condition, usually age-related, most commonly affecting adults over the age of 50, wherein damage incurred by the retina causes the loss of central vision. Wet macular degeneration may be treated with anti-angiogenic injections or photodynamic therapy. Dry macular degeneration cannot be treated but for high-dose vitamin supplementation. Consumption of omega-3 fatty acids is believed to aid in the prevention of macular degeneration.
Magnetic Resonance Elastography (MRE): An imaging technique that utilizes magnetic resonance imaging (MRI) technology to measure tissue stiffness.
Magnetic Resonance Imaging (MRI): A radiological imaging technique used to gain detailed image of the internal structures of the body. An MRI makes use of magnetic fielding and radio frequency to construct scanned images, rather than ionizing radiation, as is used in X-ray.
Malacia: The abnormal softening of a substance. For example, osteomalacia refers to the softening of bones resulting from mineralization.
Malady: Disease.
Malaise: The general feeling of being unwell; a common, primary indication of the onset of an infection or disease.
Malaria: An infectious disease prevalent in tropical and sub-tropical regions, mosquito-borne, caused by protozoan parasites of the Plasmodium genus.
Malignancy: The tendency for a condition or tumour to progressively worsen. Also refers a cancerous tumour.
Malignant: An adjective used to describe a severe, worsening condition. Malignant tumour is a term used to describe a cancerous tumour that may possess the capability to metastasize, or spread, to other tissues.
Malleus: The tiny, mallet-shaped bone of the middle ear, responsible for the transmitting vibrations from the eardrum to the incus middle-ear bone.
Mammary Gland: An exocrine gland located in the breast, responsible for the production of breast milk.
Mammogram: A low-dose X-ray imaging technique used to detect abnormalities in screening for breast cancer.
Marrow: Referring to bone marrow.
Mastectomy: The partial or total surgical removal of the breast, usually conducted in the treatment of breast cancer.
Mastitis: Inflammation of the breast, usually occurring in females while breastfeeding (puerperal mastitis). Mastitis causes the milk ducts to become blocked, thereby impeding the natural removal of milk from the breast. Antibiotics are, in most cases, successful in treating mastitis. Breast cancer may also cause mastitis symptoms, thus a visit should be made to a health care professional if signs, such as swelling, pain during breastfeeding, malaise, fever and aching, occur.
Measles: A viral-induced infection of the respiratory system, marked by skin rash, fever, cough, red eyes, and runny nose. Also called rubeola.
Medulla Oblongata: Situated at the base of the brain stem, the medulla oblongata is responsible for administrating autonomic functions. This includes hear rate, blood pressure, respiration and reflex activities such as swallowing, vomiting and sneezing.
Melanoma: A malignancy of the melanocyte, a dark pigment-producing cell most commonly found in the skin. Melanoma may also occur in the eye and the bowel. Melanoma may be caused by the striking of the chromophore of a skin cell by a UV photon, or in erroneous DNA replication. Surgical removal of the malignant tumour remains the highest result-yielding treatment option.
Melatonin: A hormone secreted by the pineal gland, involved in the body's system for regulating the sleep-wake cycle. Melatonin produces the feeling of drowsiness. Melatonin production is inhibited in light. Melatonin has had positive effects in the treatment of migraines, cluster headaches, sleep disorders, mood disorders, cancer and fertility.
Meninges: The three layers composing the system of membranes that function to coat and protect the central nervous system. The outermost meninx layer is called the dura mater, the central layer the arachnoid membrane, and the innermost of the meninges the pia mater.
Meningitis: Inflammation of the meninges, in most cases induced by viral or bacterial infection. Left untreated, meningitis almost always leads to death, and thus is classified as a medical emergency. Meningitis vaccination is available in many countries. Once contracted, individuals with meningitis must receive immediate medical attention and be treated with antibiotics or antiviral drugs.
Merkel Cell Carcinoma: A rapidly metastasizing cancer of the skin or hair follicles, usually developing in areas largely sun-exposed in adults over the age of 60. In most cases, Merkel cell polyomavirus develops from the Merkel cell polyomavirus. Early detection and treatment are paramount in halting Merkel cell carcinoma before the malignancy spreads to other tissues. These treatments can include surgical removal of cancerous legions, radiation therapy and chemotherapy.
Metastasis: The spread of cancer or other disease from the location or tumour in which the condition originated to other tissues or organs.
Micro-: Prefix defining small.
Microtia: A congenital deformity in which one or both outer ears (the pinna) develops abnormally small in size.
Microvascular Disease: Disease of the micro blood vessels of the body, sometimes as a result of long-term diabetes. Blood vessels affected may include the capillaries.
Migraine: A moderate to severe headache, often occurring in periodic succession, which may be accompanied by dizziness, increased sensitivity to light and sound (phonophobia and photophobia, respectively), blurred vision, nausea and vomiting. Triggers include strong scents, alcohol consumption, loud noise, bright light, changes in hormonal levels, lack of sleep, and hunger.
Migraine Aura: A perceptual sensation that many migraine sufferers experience before the onset of a migraine, similar to that which an epileptic often experiences prior to the onset of a seizure. A migraine aura may include the perception of strange light or scent, or a general state of confusion.
Molluscum Contagiosum: A contagious, viral skin disease marked by the presence of rounded, pearly, soft benign tumours of the skin. Can be treated though usually clears naturally. Prevalent mainly in children and teenagers. Can be transmitted sexually.
Mono: Slang for mononucleosis.
Mononucleosis: An infection of the Epstein-Barr virus causing an increase of odd lymphocytes in the blood stream. Also called mono or the kissing disease. Incubation period usually lasts a duration of four to eight weeks, inducing fatigue, sore throat, swollen lymph glands and fever.
Monosomy: The failure of one of a pair of chromosomes to develop. The only case in which humans can survive from this full aneuploidy is in the instance of Turner syndrome, wherein a female is born with only one X chromosome instead of two.
Monozygotic Twins: Identical twins, occurring when one egg is fertilized to form one zygote, from which two embryos develop.
Morbidity: Referring to a diseased or unwell state of being.
Motor Neuron Disease: A group of neurological disorders targeting motor neurons, marked by a progressive deterioration of these cells, which function to control voluntary muscle movements such as breathing, walking and the ability to speak, eat and swallow. Also termed amyotrophic lateral sclerosis, motor neuron diseases usually take onset sporadically. Treatment focuses on pain and symptom relief through physical and drug therapy.
MRI: See Magnetic Resonance Imaging.
Muir-Torre Syndrome: A genetic cancer syndrome, usually marked by an increased susceptibility to develop sebaceous skin tumours, colon cancers, breast cancer and/or keratoacanthoma (cancerous lesions of the skin).
Multiple Sclerosis(MS): An inflammatory disease wherein the body's immune system attacks and damages the myelin sheath, the dielectric material surrounding the axons of the spinal chord and brain, paramount in the transmission of nerve signals within the central nervous system. MS, also called disseminated sclerosis, inhibits normal communication between nerve cells, thereby causing a wide array of physical and mental neurological symptoms. These may include muscle weakness, loss of coordination and bladder control, impeded speech and vision capabilities, and reduced cognitive abilities. Treatment focuses on relief of symptoms and prevention of myelin attacks. Causes is believed to be a combination of environmental, genetic and infectious factors.
Mumps: An acute, viral disease causing the salivary glands to swell. Mumps can cause infections in other organs, but generally clears without complication. Reinfection very rarely occurs.
Murmur: See Heart Murmur.
Muscular Dystrophy (MD): A grouping of genetic diseases of the muscles, causing the progressive degeneration of muscle cells and tissue vital in voluntary movement. Treatment varies based on type or form of the muscular dystrophy, but tends to focus on physical therapy and, in some cases, corrective orthopedic surgery.
Mutism: Refers to selective mutism or muteness, in which the individual appears unable to speak, despite their physiological ability to do so. Most commonly associated with anxiety or trauma.
Myalgia: Muscle pain, common in many conditions and disorders.
Myco-: Prefix defining a relationship to fungus.
Mycoplasma: A large genus of bacteria, several species of which are pathogenic to humans and may be resilient to antibiotics. These species include that which is integral in the onset of atypical pneumonia and other disorders of the respiratory system.
Myeloma: Cancer of the plasma cells, white blood cells responsible for antibody production. Myeloma accumulates in the bone marrow, or within the bones, giving rise to bone lesions and bone pain, usually felt in the spine and in the ribcage. Treatment aims to prevent metastasizing, target the malignant cells, prevent bone fracture and treat myeloma-induced anemia.
Myo- (prefix): Prefix defining a relationship to muscle.
Myocardial Infarction (MI): See Heart Attack.
Myocarditis: Inflammation of the heart muscle, caused by any of numerous conditions, though usually induced by viral infection.
Myocardium: Muscle of the heart.
Myomectomy: Surgical removal of fibroid from the female uterus, leaving the uterus fully intact and functional, conducted when the fibroid is causing pain, applying pressure or interfering with reproductive processes.
Myopathy: Any disease of the muscle affecting muscle weakness.
Myopia: Nearsightedness or shortsightedness. A refractive disorder of the eye, which causes light to focus in front of the retina, meaning images that are far away are hard to distinguish. Eye glasses, biofeedback and refractive surgery are all treatment options available dependent on the degree to which the eye is myopic.
Myositis: Inflammation of the muscle tissue which may be induced by injury, medication, or diseases.
Myxoma: A tumour formed of primitive connective tissue, usually developing in the left or right heart atrium. Myxomas may be removed surgically.