DEFINITION Non-Hodgkin’s lymphoma, also called non-Hodgkin lymphoma, is cancer that originates in your lymphatic system, the disease-fighting network spread throughout your body. In non-Hodgkin’s lymphoma, tumors develop from lymphocytes — a type of white blood cell. Non-Hodgkin’s lymphoma is more…
DEFINITION Nonalcoholic fatty liver disease is a term used to describe the accumulation of fat in the liver of people who drink little or no alcohol. Nonalcoholic fatty liver disease is common and, for most people, causes no signs and…
DEFINITION Myelofibrosis is a serious bone marrow disorder that disrupts your body’s normal production of blood cells. The result is extensive scarring in your bone marrow, leading to severe anemia, weakness, fatigue, and often, an enlarged spleen and liver. Myelofibrosis…
DEFINITION Myocardial ischemia occurs when blood flow to your heart muscle is decreased by a partial or complete blockage of your heart’s arteries (coronary arteries). The decrease in blood flow reduces your heart’s oxygen supply. Myocardial ischemia, also called cardiac…
DEFINITION Myocarditis is an inflammation of the myocardium, the middle layer of the heart wall. Myocarditis is usually caused by a viral infection. Signs and symptoms of myocarditis include chest pain, heart failure and abnormal heart rhythms. If myocarditis becomes…
DEFINITION Myoclonus refers to a quick, involuntary muscle jerk. For example, hiccups are a form of myoclonus. So are the sudden jerks, or “sleep starts,” you may experience just before falling asleep. These forms of myoclonus occur in healthy people…
DEFINITION Nail fungus is a common condition that begins as a white or yellow spot under the tip of your fingernail or toenail. As the fungal infection goes deeper, nail fungus may cause your nail to discolor, thicken and crumble…
DEFINITION Narcissistic personality disorder is a mental disorder in which people have an inflated sense of their own importance, a deep need for admiration and a lack of empathy for others. But behind this mask of ultraconfidence lies a fragile…
DEFINITION Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. People with narcolepsy often find it difficult to stay awake for long periods of time, regardless of the circumstances. Narcolepsy can cause serious…
DEFINITION Nasal and paranasal tumors are abnormal growths that begin in and around the passageway between your nose and mouth (nasal cavity). Nasal tumors begin in the nasal cavity. Paranasal tumors begin in air-filled chambers around the nose called the…
DEFINITION Nasopharyngeal (nay-zo-fuh-RIN-gee-uhl) carcinoma is cancer that occurs in the nasopharynx, which is located behind your nose and above the back of your throat. Nasopharyngeal carcinoma is rare in the United States. In other parts of the world — specifically…
DEFINITION Nephrogenic systemic fibrosis is a rare disease that occurs mainly in people with advanced acute kidney failure or those who are receiving dialysis. The disease causes extensive patches of thickened and hardened skin. Nephrogenic systemic fibrosis can also affect…