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 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…
DEFINITION Neck pain is a common complaint. Neck muscles can be strained from poor posture — whether it’s leaning into your computer at work or hunching over your workbench at home. Wear-and-tear arthritis also is a common cause of neck…
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 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 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 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 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 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 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 Methicillin-resistant Staphylococcus aureus (MRSA) infection is caused by a strain of staph bacteria that’s become resistant to the antibiotics commonly used to treat ordinary staph infections. Most MRSA infections occur in people who’ve been in hospitals or other health…
DEFINITION Mosquito bites are the itchy bumps that appear after mosquitos use their mouthparts to puncture your skin and feed on your blood. Most mosquito bites are harmless, but occasionally a mosquito bite causes a large area of swelling, soreness…