Amyotrophic lateral sclerosis (a-mi-o-TROE-fik LAT-ur-ul skluh-ROE-sis), or ALS, is a nervous system (neurological) disease that causes muscle weakness and impacts physical function.
ALS is often called Lou Gehrig's disease, after the famous baseball player who was diagnosed with it. ALS is a type of motor neuron disease that causes nerve cells to gradually break down and die. In the United States, ALS is sometimes called motor neuron disease.
In most cases, doctors don't know why ALS occurs. A small number of cases are inherited.
ALS often begins with muscle twitching and weakness in an arm or leg, or sometimes with slurring of speech. Eventually, ALS can affect your ability to control the muscles needed to move, speak, eat and breathe. ALS can't be cured and eventually leads to death.
Early signs and symptoms of ALS include:
- Difficulty walking, tripping or difficulty doing your normal daily activities
- Weakness in your leg, feet or ankles
- Hand weakness or clumsiness
- Slurring of speech or trouble swallowing
- Muscle cramps and twitching in your arms, shoulders and tongue
- Difficulty holding your head up or keeping a good posture
The disease frequently begins in your hands, feet or limbs, and then spreads to other parts of your body. As the disease advances, your muscles become progressively weaker. This weakness eventually affects chewing, swallowing, speaking and breathing.
However, ALS doesn't usually affect your bowel or bladder control, your senses, or your thinking ability. It's possible to remain actively involved with your family and friends.
In ALS, the nerve cells that control the movement of your muscles gradually die, so your muscles progressively weaken and begin to waste away.
ALS is inherited in 5 to 10 percent of cases. The other cases appear to occur randomly.
Researchers are studying several possible causes of ALS, including:
- Gene mutation. Various genetic mutations can lead to inherited ALS, which appears nearly identical to the noninherited form.
- Chemical imbalance. People with ALS generally have higher than normal levels of glutamate, a chemical messenger in the brain, around the nerve cells in their spinal fluid. Too much glutamate is known to be toxic to some nerve cells.
- Disorganized immune response. Sometimes a person's immune system begins attacking some of his or her body's own normal cells, which may lead to the death of nerve cells.
Protein mishandling. Mishandled proteins within the nerve cells may lead to a gradual accumulation of abnormal forms of these proteins in the cells, eventually causing the nerve cells to die.
Established risk factors for ALS include:
- Heredity. Five to 10 percent of the people with ALS inherited it (familial ALS). In most people with familial ALS, their children have a 50-50 chance of developing the disease.
- Age. ALS most commonly occurs in people between the ages of 40 and 60.
- Sex. Before the age of 65, slightly more men than women develop ALS. This sex difference disappears after age 70.
It may be that in some people ALS, is triggered by certain environmental factors.
Also, some studies examining the entire human genome (genome-wide association studies) found numerous genetic variations that people with familial ALS and some people with noninherited ALS had in common. These genetic variations might make people more susceptible to ALS.
Environmental factors under study that may modify a person's individual risk of ALS include:
- Smoking. Smoking cigarettes appears to increase a person's risk of ALS to almost twice that of a nonsmoker. The more years spent smoking, the greater the risk. However, quitting smoking can eventually lower the increased risk.
- Lead exposure. Some evidence suggests that exposure to lead in the workplace may be associated with the development of ALS.
Military service. Recent studies indicate that people who have served in the military are at higher risk of ALS. Exactly what about military service may trigger the development of ALS is uncertain, but it may include exposure to certain metals or chemicals, traumatic injuries, viral infections and intense exertion.
As the disease progresses, people with ALS experience complications, which may include:
Over time, ALS paralyzes the muscles needed to breathe. Some devices to assist your breathing are worn only at night and are similar to devices used by people with sleep apnea. For example, you may be given noninvasive positive pressure ventilation to assist with your breathing at night.
In the latter stages of ALS, some people choose to have a tracheostomy — a surgically created hole at the front of the neck leading to the windpipe (trachea) — to enable the full-time use of a respirator that inflates and deflates their lungs.
The most common cause of death for people with ALS is respiratory failure. On average, death occurs within three to five years after symptoms begin.
Most people with ALS will develop trouble speaking over time. This usually starts as some mild slurring of words, often intermittently, but progresses over time to be more severe. With time, speech becomes more difficult for others to understand, and people with ALS often rely on other communication technologies to communicate.
When the muscles that control swallowing are affected, people with ALS can develop malnutrition and dehydration. They are also at higher risk of getting food, liquids or saliva into the lungs, which can cause pneumonia. A feeding tube can reduce these risks.
Some people with ALS experience problems with memory and making decisions, and some are eventually diagnosed with a form of dementia called frontotemporal dementia.
If you're having some of the early signs and symptoms of a neuromuscular disease such as ALS, you might first consult your family doctor, who will listen to your description of symptoms and do an initial physical examination. Then your doctor will probably refer you to a doctor trained in nervous system conditions (neurologist) for further evaluation.
What you can do
Once you're under the care of a neurologist, it may still take time to establish the diagnosis.
If you've been referred to certain medical centers, your evaluation may involve an integrated team of neurologists, and other doctors and health care professionals trained in different aspects of motor neuron disease.
Doctors will give you a comprehensive evaluation to diagnose your condition. However, this process can be stressful and frustrating unless your medical team keeps you informed. These strategies may give you a greater sense of control.
- Keep a symptom diary. Before you see a neurologist, start using a calendar or notebook to jot down the time and circumstances each time you notice problems with walking, hand coordination, speech, swallowing or involuntary muscle movements. Your observations may reveal a pattern that aids diagnosis.
- Find a neurologist and care team. Generally, an integrated care team led by your neurologist is most appropriate for your ALS care. Your team should communicate and be familiar with your individual needs.
An integrated team may prolong survival and improve your quality of care.
What to expect from your doctor
Your family doctor will carefully review your family's medical history and your signs and symptoms. Your neurologist and your family doctor may conduct a physical and neurological examination, which may include testing:
- Muscle strength
- Muscle tone
- Senses of touch and sight
Amyotrophic lateral sclerosis (ALS) is difficult to diagnose early because it may appear similar to several other neurological diseases. Tests to rule out other conditions may include:
Electromyogram (EMG). During an EMG, your doctor inserts a needle electrode through your skin into various muscles. The test evaluates the electrical activity of your muscles when they contract and when they're at rest.
Abnormalities in muscles seen in an electromyogram can help doctors diagnose ALS, or determine if you have a muscle or nerve condition that may be causing your symptoms. It can also help guide your exercise therapy.
- Nerve conduction study. This study measures your nerves' ability to send impulses to muscles in different areas of your body. This test can determine if you have nerve damage or certain muscle diseases.
- Magnetic resonance imaging (MRI). Using radio waves and a powerful magnetic field, an MRI can produce detailed images of your brain and spinal cord. An MRI can evaluate if you have spinal cord tumors, herniated disks in your neck or other conditions that may be causing your symptoms.
- Blood and urine tests. Analyzing samples of your blood and urine in the laboratory may help your doctor eliminate other possible causes of your signs and symptoms.
- Spinal tap (lumbar puncture). Sometimes a specialist may remove a sample of your spinal fluid for analysis. In this procedure, a specialist inserts a small needle between two vertebrae in your lower back and removes a small amount of cerebrospinal fluid for testing in the laboratory.
- Muscle biopsy. If your doctor believes you may have a muscle disease rather than ALS, you may undergo a muscle biopsy. In this procedure, while you're under local anesthesia a small portion of your muscle is removed and sent to a lab for analysis.
Because there's no reversing the course of amyotrophic lateral sclerosis, treatments focus on slowing the progression of symptoms, preventing unnecessary complications and making you more comfortable and independent.
Because ALS involves complex physical, mental and social issues, you may find it helpful to have an integrated team of doctors trained in many areas and other health care professionals provide your care. Having an integrated team of doctors and other health care professionals manage your ALS care may prolong your survival and improve your quality of life.
Your team will help you select the right treatments for you. You always retain the right to choose or not choose any of the treatments suggested.
The drug riluzole (Rilutek) is the only medication approved by the Food and Drug Administration for ALS. The drug appears to slow the disease's progression in some people, perhaps by reducing levels of a chemical messenger in the brain (glutamate) that's often present in higher levels in people with ALS.
Riluzole may cause side effects such as dizziness, gastrointestinal conditions and liver function changes.
Your doctor may also prescribe medications to provide relief from other symptoms, including:
- Muscle cramps and spasms
- Excessive salivation
- Excessive phlegm
- Sleep problems
- Uncontrolled outbursts of laughing or crying
Breathing care. Over time, you'll have more difficulty breathing as your muscles become weaker. Doctors may test your breathing regularly and provide you with devices to assist your breathing at night.
In some cases, you may choose to breathe through mechanical ventilation. Doctors insert a tube in a surgically created hole at the front of your neck leading to your windpipe (tracheostomy), and the tube is connected to a respirator.
Physical therapy. A physical therapist can address pain, walking, mobility, bracing and equipment needs that help maintain your independence. Some measures include low-impact exercises to maintain your cardiovascular fitness, muscle strength and range of motion for as long as possible.
A physical therapist can also help you become accustomed to a brace, walker or wheelchair and may be able to suggest devices such as ramps that make it easier for you to get around.
Regular exercise can also help improve your sense of well-being. Appropriate stretching can help prevent pain and help your muscles function at their best.
Occupational therapy. An occupational therapist can help you compensate for hand and arm weakness in a manner that helps you to keep your independence for as long as possible. Adaptive equipment can help you to continue to perform daily activities such as dressing, grooming, eating and bathing.
An occupational therapist can also help you understand how to modify your home to allow accessibility if you become less able to walk safely.
Occupational therapists also have a good understanding of how assistive technology and computers can be used, even if your hands are weak.
Speech therapy. Because ALS affects the muscles you use to speak, communication becomes an issue as the disease progresses. A speech therapist can teach you adaptive techniques to make your speech more clearly understood. Speech therapists can also help you explore other methods of communication, such as an alphabet board or simple pen and paper.
Later in disease progression, a speech therapist can recommend devices such as tablet computers with text-to-speech applications or computer-based equipment with synthesized speech that may help you communicate. Ask your therapist about the possibility of borrowing or renting these devices.
- Nutritional support. Your team will work with you and your family members to ensure you're eating foods that are easier to swallow and meet your nutritional needs. You may eventually need a feeding tube.
- Psychological and social support. Your team may include a social worker to help with financial issues, insurance, and getting equipment and paying for devices you may need. Psychologists, social workers and others may provide emotional support for you and your family.
Learning you have ALS can be devastating. The following tips may help you and your family cope:
- Take time to grieve. The news that you have a fatal condition that will reduce your mobility and independence can be difficult to absorb. If you are newly diagnosed, you and your family will likely experience a period of mourning and grief.
- Be hopeful. Your team will help you focus on your ability and healthy living. Some people with amyotrophic lateral sclerosis live much longer than the three to five years usually associated with this condition. Some live 10 years or more. Maintaining an optimistic outlook can help improve quality of life for people with ALS.
- Think beyond the physical changes. Many people with amyotrophic lateral sclerosis lead rich, rewarding lives despite physical limitations. Try to think of ALS as only one part of your life, not your entire identity.
- Join a support group. You may find comfort in sharing your concerns in a support group with others who have ALS. Your family members and friends helping with your care also may benefit from a support group of others who care for people with amyotrophic lateral sclerosis. Find support groups in your area by talking to your doctor or by contacting the ALS Association.
Make decisions now about your future medical care. Planning for the future allows you to be in control of decisions about your life and your care.
With the help of your doctor, hospice nurse or social worker, you can decide whether you want certain life-extending procedures.
You can also determine where you want to spend your final days. You may consider hospice care options. Planning for the future can help you and your loved ones put to rest some common anxieties.
- Experience. Mayo Clinic doctors trained in neuromuscular conditions (neurologists) have extensive experience treating amyotrophic lateral sclerosis (ALS). Mayo Clinic doctors evaluate and treat more than 700 people with ALS each year.
Team approach. At Mayo Clinic, neurologists work as a team with doctors trained in physical medicine and rehabilitation (physiatrists), physical and occupational therapists, nutrition specialists (dietitians), nurses, social workers and others to treat people with ALS. Depending on your need, many health care professionals are available and willing to become part of your team.
The integrated team is committed to providing for your needs and managing your condition through continuing care and follow-up appointments.
Doctors trained in amyotrophic lateral sclerosis diagnose and treat people with ALS at Mayo Clinic in Arizona, Florida and Minnesota.
- Expertise. The ALS Association has certified Mayo Clinic in Arizona, Florida and Minnesota as Centers of Excellence.
- Comprehensive care. Doctors offer comprehensive care for people with ALS and their families, coordinating their diagnostic tests, treatment, rehabilitation, nutrition, lung and breathing care (pulmonary care), and follow-up care. Doctors offer treatment and continuing care that can address your medical needs and improve your quality of life.
- Support. Mayo Clinic offers you and your family many resources for support, information and education. Your treatment team partners with you and your family to provide care and support. Support groups for people with ALS and their family members are available throughout the United States, and your treatment team can work with you to find support groups in your area.
Mayo Clinic in Rochester, Minn., ranks #1 for neurology and neurosurgery in the U.S. News & World Report Best Hospitals rankings. Mayo Clinic in Scottsdale, Ariz., is ranked among the Best Hospitals for neurology and neurosurgery, and Mayo Clinic in Jacksonville, Fla., is ranked high performing for neurology and neurosurgery by U.S. News & World Report.
At Mayo Clinic, we assemble a team of specialists who take the time to listen and thoroughly understand your health issues and concerns. We tailor the care you receive to your personal health care needs. You can trust our specialists to collaborate and offer you the best possible outcomes, safety and service.
Mayo Clinic is a not-for-profit medical institution that reinvests all earnings into improving medical practice, research and education. We're constantly involved in innovation and medical research, finding solutions to improve your care and quality of life. Your doctor or someone on your medical team is likely involved in research related to your condition.
Our patients tell us that the quality of their interactions, our attention to detail and the efficiency of their visits mean health care — and trusted answers — like they've never experienced.
Why Choose Mayo Clinic
What Sets Mayo Clinic Apart
Mayo Clinic doctors who have training in neuromuscular conditions (neurologists) have experience diagnosing Lou Gehrig's disease (ALS) and other brain (neurological) conditions that may cause your symptoms. You often can be evaluated and tested for ALS within two or three days.
Lou Gehrig's disease can be difficult to diagnose in its early stages because the symptoms are similar to many other disorders, including spinal cord diseases, muscle diseases and neurological diseases such as multiple sclerosis, multifocal motor neuropathy, myasthenia gravis, spinal muscular atrophy and stroke. Doctors at Mayo Clinic have experience evaluating people for ALS and other conditions with similar symptoms.
To diagnose your condition, your neurologist will discuss your symptoms and any family history of neuromuscular diseases. Your neurologist will give you a complete physical examination and check for signs of muscle weakness. Your doctor may order various tests, including tests to rule out other conditions.
Diagnostic tests may include:
- Blood tests. Your doctor may use blood tests to check for the enzyme creatine kinase (CK), which leaks out of damaged muscle, or other blood tests for conditions that mimic Lou Gehrig's disease (ALS). Blood tests can also be used for genetic testing to detect familial ALS, which occurs when ALS is present in two or more family members related by blood.
- Cerebrospinal fluid examination. Your doctor may examine the cerebrospinal fluid surrounding your brain and spinal cord. In this test, a specialist will insert a needle into your lower back to withdraw a small amount of spinal fluid in a procedure called a spinal tap or lumbar puncture.
- Electromyogram (EMG). This test measures the tiny electrical signals in muscles. A specialist inserts a thin-needle electrode into the muscle to be tested. An instrument records the electrical activity in the muscle when it's at rest and when it contracts. An EMG may indicate that the motor nerves aren't functioning, yet the sensory nerves are normal, a sign of Lou Gehrig's disease.
- Genetic testing. Sometimes your doctor may perform genetic testing to test for some forms of familial ALS and for other neurological conditions with similar symptoms.
- Magnetic resonance imaging (MRI). This test uses powerful magnets and radio waves to produce a detailed view of your nervous system. Your doctor may order an MRI of your brain or spine to rule out other conditions.
- Muscle biopsy. To determine if you have a muscle disorder (myopathy) such as myositis or muscular dystrophy, rather than ALS, you may have a muscle biopsy. A specialist removes a small amount of tissue from a muscle to test.
- Nerve conduction study (NCS). This test measures electrical nerve impulses and functioning in your muscles and nerves. A specialist places two electrodes on your skin. A small shock is passed through the nerve to measure the electrical impulses in the nerve signals.
- Respiratory testing. Your doctor may order respiratory tests to determine if your condition affects the muscles that control your breathing.
Doctors with training in neuromuscular conditions (neurologists), physical medicine and rehabilitation specialists, physical and occupational therapists, speech therapists, swallowing disorder specialists, nutrition specialists (dietitians), social workers and other specialists work together as a team to treat many people each year who have Lou Gehrig's disease (ALS). The integrated team is committed to providing for your needs and managing your condition through continuing care and follow-up appointments.
The treatment team meets regularly to discuss the most appropriate care for people who have Lou Gehrig's disease (ALS). Although ALS can't be cured, doctors focus on slowing the progression of your condition, relieving your symptoms, helping you maintain function through rehabilitation and improving your quality of life. The team partners with you and your family to provide care and support.
- Medications. Your doctor decides whether to manage your condition with medications based on your symptoms and the severity of your condition. Your doctors may prescribe other medications to reduce nerve damage, control muscle spasms and stiffness, and reduce symptoms such as fatigue, pain, sleep disturbances, constipation, and excess saliva and phlegm. You may need several medications.
- Physical and occupational therapy. In physical therapy, you may perform low-impact exercises such as walking, swimming and stationary-bicycle riding to strengthen your muscles, improve your heart (cardiovascular) health and fight fatigue and depression. You also may perform range-of-motion and stretching exercises to help prevent muscle spasms and cramping and maintain your range of motion. In occupational therapy, you may learn to use assistive devices such as a wheelchair.
- Speech therapy. Lou Gehrig's disease affects the muscles you use to speak. A speech therapist can teach you how to speak more clearly to be better understood. As your disease progresses, you may learn to use devices such as speech synthesizers and computers to communicate.
- Assistive devices. Assistive devices can help you maintain as much mobility as possible. Braces can support weakened muscles in your limbs. Canes, walkers and wheelchairs also can help with mobility. As Lou Gehrig's disease weakens muscles you use to breathe, you may need a breathing machine (a mask or a ventilator) to assist with your breathing.
- Nutritional support. A nutrition specialist can offer you advice about nutritious foods that are easy to swallow. As Lou Gehrig's disease progresses, you may eventually need to have a feeding tube inserted into your stomach for nutrition.
- Mental health care. As Lou Gehrig's disease progresses, your mind, personality, intelligence, memory and senses usually aren't affected. You're usually aware that you're losing muscle function. Some people become anxious and depressed and benefit from medication and counseling.
- Family support. Your family members may need help coping with your disease and its challenges. Your treatment team offers various resources, education and information for your family. Also, your family members can ask your treatment team for information about connecting with local ALS support groups.
- Follow-up care. Mayo Clinic doctors provide coordinated treatment and follow-up care for people who have Lou Gehrig's disease and will work closely with your primary care or local doctor.
Mayo Clinic works with hundreds of insurance companies and is an in-network provider for millions of people. In most cases, Mayo Clinic doesn't require a physician referral. Some insurers require referrals or may have additional requirements for certain medical care. All appointments are prioritized on the basis of medical need.
Doctors trained in neurology work with doctors in several areas to care for people with amyotrophic lateral sclerosis (ALS) at Mayo Clinic in Arizona.
The ALS Center staff includes doctors with training in neuromuscular conditions (neurologists), physical and occupational therapists, a speech and language pathologist, a social worker, a nutrition specialist (dietitian), a breathing (respiratory) therapist and a nurse coordinator.
For appointments or more information, call the Central Appointment Office at 800-446-2279 (toll-free) 8 a.m. to 5 p.m. Mountain Standard Time, Monday through Friday or complete an online appointment request form.
- U.S. Patients
- International Patients
The ALS Center at Mayo Clinic in Florida offers integrated, supportive care and information for people with amyotrophic lateral sclerosis (ALS), their families and caregivers. The team works closely with the ALS Association and the Muscular Dystrophy Association.
For appointments or more information, call the Central Appointment Office at 904-953-0853 8 a.m. to 5 p.m. Eastern time, Monday through Friday or complete an online appointment request form.
- U.S. Patients
- International Patients
The Amyotrophic Lateral Sclerosis Subspecialty Group at Mayo Clinic in Minnesota offers comprehensive care for people with amyotrophic lateral sclerosis (ALS) and their families. The team works closely with the ALS Association.
For appointments or more information, call the Central Appointment Office at 507-538-3270 7 a.m. to 6 p.m. Central time, Monday through Friday or complete an online appointment request form.
- U.S. Patients
- International Patients
Researchers at Mayo Clinic in Arizona, Florida and Minnesota actively study possible causes of amyotrophic lateral sclerosis (ALS). Research includes identifying biomarkers in blood and cerebrospinal fluid that may someday help to identify and monitor loss of motor neurons in ALS and aid in monitoring response to treatment.
Research also includes identifying genes that may cause or contribute to the development of ALS. Researchers study genes that may predict people who are at high risk of ALS.
In addition, researchers study potential new treatments for people with ALS and ALS-related diseases and participate in clinical trials of potential new medications. For example, researchers study how stem cells potentially may be used to prevent cell death and tissue damage.
Read more about research in neuromuscular diseases and amyotrophic lateral sclerosis (ALS). Also read about genetic analysis of novel and known genes implicated in frontotemporal dementia and amyotrophic lateral sclerosis and research in therapy for ALS.
Read more about monitoring and treating ALS.
Mayo Clinic publications
See a list of publications by Mayo Clinic doctors on amyotrophic lateral sclerosis on PubMed, a service of the National Library of Medicine.
Apr. 09, 2014
- Amyotrophic lateral sclerosis fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/amyotrophiclateralsclerosis/detail_amyotrophiclateralsclerosis.htm. Accessed Sept. 28, 2010.
- Elman LB, et al. Clinical features of amyotrophic lateral sclerosis. http://www.uptodate.com/home/index.html. Accessed Sept. 28, 2010.
- Maragakis NJ, et al. Epidemiology and pathogenesis of amyotrophic lateral sclerosis. http://www.uptodate.com/home/index.html. Accessed Sept. 28, 2010.
- McCluskey L. Familial amyotrophic lateral sclerosis. http://www.uptodate.com/home/index.html. Accessed Sept. 28, 2010.
- Neurological diagnostic tests and procedures. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/misc/diagnostic_tests.htm. Accessed Sept. 28, 2010.
- ALS in the military: Unexpected consequences of military service. ALS Association. http://www.alsa.org/files/pdf/als_military_paper.pdf. Accessed Sept. 28, 2010.
- Elman LB, et al. Diagnosis of amyotrophic lateral sclerosis. http://www.uptodate.com/home/index.html. Accessed Sept. 28, 2010.
- Galvez-Jimenez N, et al. Symptom-based management of amyotrophic lateral sclerosis. http://www.uptodate.com/home/index.html. Accessed Sept. 28, 2010.
- Choudry RB, et al. Pharmacologic treatment of amyotrophic lateral sclerosis. http://www.uptodate.com/home/index.html. Sept. 28, 2010.
- Why is exercise important? In: Everyday Life With ALS: A Practical Guide. Muscular Dystrophy Association. http://www.als-mda.org/publications/everydaylifeals/ch8/. Accessed Sept. 28, 2010.
- Miller RG, et al. Practice parameter update: The care of the patient with amyotrophic lateral sclerosis: Multidisciplinary care, symptom management, and cognitive/behavioral impairment (an evidence-based review): Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2009;73:1227.
- Miller RG, et al. Practice parameter update: The care of the patient with amyotrophic lateral sclerosis: Drug, nutritional, and respiratory therapies (an evidence-based review): Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2009;73:1227.
- Covering all the bases. ALS Association. http://www.alsa.org/coveringallthebases/. Accessed Oct. 21, 2010.
- Armon C. Smoking may be considered an established risk factor for sporadic ALS. Neurology. 2009;73:1693.
- Gallo V, et al. Smoking and risk for amyotrophic lateral sclerosis: Analysis of the EPIC cohort. Annals of Neurology. 2009;65:378.
- Mayadev AS, et al. The amyotrophic lateral sclerosis center: A model of multidisciplinary management. Physical Medicine and Rehabilitation Clinics of North America. 2008;19:619.
- Crum BA (expert opinion). Mayo Clinic, Rochester, Minn. Oct. 6, 2010.