Metabolic surgery is a type of operation that changes your digestive system to help you lose weight and improve serious health conditions related to obesity, including type 2 diabetes and heart disease.

Metabolic syndrome affects about 1 in 3 adults in the United States. This group of conditions includes extra belly fat, high blood pressure, high blood sugar, and unhealthy cholesterol levels—all working together to significantly raise your risk for heart disease, stroke, and type 2 diabetes.

Metachromatic leukodystrophy is a rare inherited disorder that progressively destroys the protective covering around nerve cells in the brain and nervous system. This buildup of fatty substances leads to a gradual loss of physical abilities, mental function, and eventually results in severe disability.

When cancer from other parts of the body spreads to the bile ducts, it creates a rare and challenging situation that requires specialized care and understanding.

When cancer spreads from other parts of the body to the brain or spinal cord, it creates metastases to the central nervous system. These tumors are far more common than cancers that start in the brain itself, and modern medicine now offers more treatment options than ever before.

When cancer spreads from another part of the body to the liver, it creates a condition that is far more common than cancer that starts in the liver itself. Understanding this disease, recognizing its symptoms, and knowing the treatment options available can help patients and their families navigate this challenging diagnosis.

When cancer spreads beyond its original location, lymph nodes are often the first place it travels to. Understanding how cancer moves through the lymphatic system and what it means for treatment can help patients navigate this challenging diagnosis.

When cancer spreads to the thin membranes surrounding the brain and spinal cord, it creates a rare but serious condition that affects thousands of people each year. Understanding this disease can help patients and families navigate diagnosis, treatment options, and what to expect.

When cancer from organs like the stomach, colon, or ovaries spreads to the membrane lining your abdomen, it creates a serious condition that requires specialized care, but new treatments are helping patients live longer and better lives.

When cancer spreads to the rectum from another part of the body, or when rectal cancer spreads to distant organs, it creates unique challenges that require specialized care and treatment approaches.

Metastasis is when cancer spreads from where it started to other parts of the body. While most cancer-related deaths happen because of metastasis, new treatments are helping some people live longer with this advanced form of the disease.

Metastatic gastric cancer occurs when cancer that started in the stomach spreads to other parts of the body, most commonly the liver, peritoneum, lungs, or bones. While this advanced stage cannot usually be cured, treatments can help control the disease, reduce symptoms, and improve quality of life.

Metastatic glioma refers to the rare situation when an aggressive brain tumor called a glioma spreads beyond the brain and spinal cord to other parts of the body. While gliomas are serious tumors that often invade surrounding brain tissue, spreading outside the central nervous system is extremely uncommon.

Metastatic melanoma occurs when melanoma, the most serious type of skin cancer, spreads from its original location to other parts of the body, most commonly to the skin, lymph nodes, lungs, liver, bones, or brain.

Metastatic neoplasm is cancer that has spread from where it first started to other parts of the body. Nearly all cancers can spread, but whether they do depends on several factors. While most metastatic cancers cannot be cured, treatments can help manage symptoms and improve quality of life.

Metastatic renal cell carcinoma is kidney cancer that has spread beyond the kidney to other parts of the body, most commonly to the lungs, bones, liver, or brain. While this advanced stage cannot be cured, modern treatments can help control the disease, manage symptoms, and improve quality of life.

Metastatic squamous cell carcinoma is a form of skin cancer that has spread beyond its original location to other parts of the body. While most squamous cell carcinomas are caught early and successfully treated, about 5 percent become advanced, making them far more dangerous and challenging to manage.

Methylmalonic acidaemia is a rare inherited disorder where the body cannot properly break down certain proteins and fats, leading to a dangerous buildup of toxic substances that can affect the brain, kidneys, and other organs throughout life.

Micrographic skin surgery is a highly specialized technique for removing skin cancer while preserving as much healthy tissue as possible, offering the highest cure rates and minimal scarring.

Microsatellite instability is a unique change in cancer cells that occurs when the body’s normal DNA repair system stops working properly, leading to genetic errors that accumulate in tumor cells and affect how cancer responds to treatment.

Microscopic polyangiitis is a rare condition where tiny blood vessels throughout the body become inflamed, potentially damaging vital organs like the kidneys and lungs. Understanding this condition can help you recognize symptoms early and work with your healthcare team to manage it effectively.

Microvillous inclusion disease is a rare inherited intestinal disorder that causes severe, life-threatening diarrhea in infants, typically beginning within hours or days after birth. The disease affects the cells lining the small intestine, making it impossible for the body to absorb nutrients and fluids from food.

Migraine is far more than just a bad headache. It’s a complex neurological condition that can leave you unable to carry out daily activities for hours or even days, causing intense throbbing pain, nausea, and extreme sensitivity to light and sound.

Migraine with aura is a recurring headache disorder where sensory disturbances called auras occur before or during the headache. These temporary symptoms, most commonly visual, can include seeing flashing lights, blind spots, or zigzag patterns, and typically last less than an hour.

Migraine without aura is the most common form of migraine, affecting roughly three out of every four people who experience this neurological condition. Unlike migraine with aura, attacks occur without warning signs like flashing lights or vision problems, but the pain and other symptoms can be just as disabling.

Milk allergy is one of the most common food allergies, especially in young children. It happens when your body’s immune system mistakenly treats milk proteins as harmful invaders, triggering reactions that can range from mild discomfort to life-threatening emergencies.

Mite allergy is a common allergic reaction caused by tiny bugs that live in household dust. These microscopic creatures thrive in warm, humid places like bedding and furniture, and their droppings can trigger symptoms ranging from sneezing and runny nose to more serious breathing problems.

Mitochondrial DNA depletion syndrome is a rare genetic condition that dramatically reduces the amount of vital DNA inside the power generators of cells, leading to severe energy failure in affected organs and tissues.

Mitochondrial myopathy affects the tiny energy factories inside our cells, leading to muscle weakness and fatigue that can impact daily life in profound ways.

Mitral valve disease affects the valve between the left upper and lower chambers of your heart. This condition can range from mild, with no symptoms, to severe, potentially leading to serious complications like heart failure if left untreated.

Mitral valve incompetence is a condition where the valve between the two left chambers of your heart doesn’t close properly, allowing blood to leak backward. This common heart valve problem can range from mild, causing no symptoms, to severe, requiring treatment to prevent serious complications.

Mitral valve prolapse is a common heart condition that affects millions of people worldwide, yet many don’t even know they have it. While most cases are harmless and require no treatment, understanding this condition can help you manage your heart health and know when to seek medical attention.

Mixed dementia is a condition where brain changes from more than one type of dementia occur at the same time. The most common form combines Alzheimer’s disease and vascular dementia, though other combinations are also possible.

Mixed-type liposarcoma is a rare and aggressive form of cancer that combines different types of liposarcoma cells within the same tumor, making it particularly challenging to treat and manage.

Mpox, formerly known as monkeypox, is a viral illness that can affect anyone through close contact with an infected person or animal. Most people recover fully within a few weeks, but understanding the symptoms and how to protect yourself can help prevent the spread of this disease.

Monogenic diabetes is a rare form of diabetes caused by a change in a single gene, making it fundamentally different from the more common type 1 and type 2 diabetes that involve multiple genes and environmental factors.

Morning sickness affects up to 70% of pregnant women, causing nausea and vomiting that can strike at any time of day—not just in the morning. While this common condition is usually harmless to both mother and baby, understanding its causes and knowing how to manage it can make the journey through pregnancy much more comfortable.

Mucopolysaccharidosis is a group of rare inherited diseases that cause progressive cellular damage throughout the body, affecting appearance, physical abilities, and organ function. These conditions result from missing or malfunctioning enzymes that normally break down complex sugar molecules, leading to their harmful accumulation in cells and tissues.

Mucopolysaccharidosis type I is a rare inherited condition that affects many parts of the body, causing progressive damage to organs, bones, and tissues due to the buildup of complex sugar molecules inside cells.

Mucopolysaccharidosis type II, also known as Hunter syndrome, is a rare genetic disorder that occurs almost exclusively in boys. This progressive condition affects many parts of the body, from physical appearance to organ function, and its severity varies greatly among affected individuals.

Mucopolysaccharidosis type III, also known as Sanfilippo syndrome, is a rare inherited disease that primarily affects the brain and spinal cord, causing progressive damage to the nervous system in early childhood.

Mucosal inflammation is a painful condition affecting the protective lining of your body’s internal passages. It can cause burning, soreness, and swelling in your mouth, digestive tract, and other areas where mucous membranes protect your body from the outside world.

Mucous membrane pemphigoid is a rare autoimmune condition that causes painful blisters primarily in the mouth and eyes, and can lead to serious complications including vision loss if not treated early.

Multifocal motor neuropathy is a rare condition where the body’s immune system mistakenly attacks nerves that control muscles, causing slowly worsening weakness mainly in the hands and arms, though treatment can help manage symptoms effectively.

Multiple sclerosis is a chronic disease where the body’s immune system mistakenly attacks the protective covering of nerve cells in the brain, spinal cord, and optic nerves. While there is no cure, modern treatments can help control the disease so effectively that many people continue living full, active lives with minimal disruption.

Multiple sclerosis relapses are episodes when new symptoms suddenly appear or existing symptoms get worse. These attacks are a key feature of the disease, especially in the relapsing-remitting form that affects most people with MS. Understanding what causes relapses and how to manage them can help you work with your healthcare team to maintain stability and quality of life.

Multiple system atrophy is a rare and progressive brain disease that causes parts of the brain to deteriorate over time, affecting movement, balance, and the body’s automatic functions like blood pressure and digestion. Though there is currently no cure, treatments and support can help manage symptoms and maintain quality of life for as long as possible.

Mumps is a contagious viral infection that causes painful swelling of the salivary glands, making the cheeks and jaw puff up. While most people recover completely within two weeks, the disease can spread easily and sometimes leads to serious complications.

Muscle hypertrophy is the process of increasing muscle size through exercise and proper nutrition. This natural response to resistance training involves the growth of muscle cells, making muscles larger and often stronger. Understanding how muscles grow can help anyone interested in building muscle mass achieve better results.

Muscle injuries are among the most common soft tissue injuries, affecting everyone from professional athletes to people doing everyday activities. These painful tears in muscle fibers can range from minor stretches to complete ruptures, but most heal with proper rest and care.

Muscle spasticity is a condition where muscles become stiff, tight, and resist being stretched, making movement difficult and sometimes painful. It affects people with various neurological conditions and can range from mild muscle tightness to severe, uncontrollable spasms that significantly impact daily life.

Muscle strains are one of the most common injuries affecting both athletes and everyday people, causing pain that can range from mild discomfort to severe tears requiring surgery. Understanding how these injuries happen and heal can help you recover safely and prevent future problems.

Muscular dystrophy is a group of more than 30 genetic diseases that cause muscles to become progressively weaker over time, making everyday activities increasingly difficult.

Myasthenia gravis is a chronic condition where communication between nerves and muscles breaks down, causing muscles to feel weak and tire quickly. While there’s no cure, effective treatments can help most people manage symptoms and live full, active lives.

Mycobacterium abscessus complex is a challenging bacterial infection found in water, soil, and dust that can cause serious health problems, particularly in people with lung disease or weakened immune systems. Treatment is difficult and requires a combination of antibiotics for many months.

Mycobacterium avium complex (MAC) infection is a bacterial disease caused by common germs found in water, soil, dust, and food. While almost everyone is exposed to these bacteria, they typically only cause illness in people with weakened immune systems or existing lung disease.

Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is a rare inflammatory condition where the immune system mistakenly attacks the protective covering of nerves in the brain, spinal cord, and eyes, causing symptoms that can range from vision loss to paralysis.

Myelodysplastic syndrome is a group of disorders that disrupts normal blood cell production in the bone marrow, leaving the body without enough healthy blood cells to function properly. While some people live with the condition for years without treatment, others may see it progress to a more aggressive form of cancer.

Myelodysplastic syndrome (MDS) is a group of blood disorders that can progress to a more serious form of cancer. Understanding what happens when MDS transforms into acute myeloid leukemia and what affects the outcome can help patients and families prepare for the challenges ahead.

Myelodysplastic syndrome with excess blasts is a high-risk form of a blood disorder where the bone marrow produces too many immature blood cells and not enough healthy ones, often leading to serious complications.