Flaccid Myelitis

What is flaccid myelitis?

Flaccid myelitis, usually called acute flaccid myelitis (AFM), is a rare but serious condition of the nervous system. “Myelitis” means inflammation of the spinal cord, the bundle of nerve tissue that runs from the brain down the back and carries signals to the muscles. “Flaccid” describes muscles that have become weak and floppy rather than stiff. In flaccid myelitis, the inflammation mainly affects the gray matter of the spinal cord, the area that contains the nerve cells (motor neurons) that tell muscles to move. When these cells are damaged, the muscles they control become weak, and in some cases they stop working.

If you are asking “what is flaccid myelitis,” the simplest answer is that it is a sudden, polio-like weakness of one or more limbs that develops over hours or days, usually shortly after a mild viral illness. It is not the same as polio, but it looks similar because both conditions damage the same part of the spinal cord.

Flaccid myelitis mostly affects children, often between the ages of about two and eight, although older children and adults can develop it. It is uncommon. In the United States, cases have tended to appear in clusters every two years or so, most often in late summer and early fall, which fits with the seasonal spread of certain viruses. Health authorities such as the Centers for Disease Control and Prevention (CDC) track reported cases closely.

Flaccid myelitis symptoms

Flaccid myelitis symptoms usually appear suddenly, and this speed is one of the features that separates the condition from many other causes of weakness. In many cases, a child first has an ordinary-looking illness such as a cold, cough, sore throat or fever. About one to two weeks later, weakness appears in an arm or a leg and may progress quickly, sometimes over a matter of hours.

The most common flaccid myelitis symptoms include:

• Sudden weakness in an arm or leg, often on one side of the body and frequently affecting the arm more than the leg
• Loss of muscle tone, so the limb feels limp or floppy
• Reduced or absent reflexes in the affected limb
• Difficulty using a limb, such as trouble lifting an arm, gripping objects, standing or walking
• Pain in the neck, back or the affected limb, which sometimes appears before the weakness
• Facial drooping or weakness, including drooping eyelids or trouble moving the eyes
• Difficulty swallowing or slurred speech
• Neck weakness, making it hard to hold the head up
• Trouble breathing, which is the most dangerous symptom because the muscles that support breathing can be affected

Unlike some other spinal cord conditions, sensation is usually preserved. A person with flaccid myelitis can typically still feel touch, temperature and pain in the weak limb, even though they cannot move it well. Bladder and bowel control are usually not affected, although this can occasionally happen. Confusion or a change in alertness is uncommon and may point to a different problem.

Symptoms can vary by stage. In the early stage, weakness is often mild and may be mistaken for a sprain, a pulled muscle or simple tiredness. Over the following days it can spread to other limbs or to the muscles of the face, throat and chest. After the acute stage, the pattern of weakness tends to become stable, and the affected muscles may begin to shrink (a change called atrophy) because they are no longer receiving normal nerve signals.

Causes and risk factors

Flaccid myelitis causes are not fully understood, but the strongest evidence points to viral infection. The most closely linked viruses are enteroviruses, a large family of common viruses that usually cause mild illnesses such as colds, fever, rashes or stomach upsets. One type, enterovirus D68 (EV-D68), has been found in a substantial share of children during outbreak years, and another type, enterovirus A71 (EV-A71), has also been associated with the condition. Poliovirus, which caused paralysis in earlier generations, is also an enterovirus and produces a similar picture, which is why doctors test for it to rule it out.

Other viruses that have been linked to flaccid myelitis or to a very similar spinal cord illness include:

• West Nile virus and related mosquito-borne viruses
• Adenoviruses
• Certain other enteroviruses and coxsackieviruses

Doctors think the virus either directly attacks the motor neurons in the spinal cord or triggers an immune response that damages them. Because the virus has often been cleared from the body by the time weakness appears, it is frequently not detected in samples taken from the spinal fluid, which makes the exact cause hard to confirm in an individual patient.

Known risk factors are limited. Most children who develop flaccid myelitis were previously healthy. Factors that appear to be associated with it include:

• Being a young child, since most reported cases occur in children
• Having had a recent respiratory illness or fever, especially during late summer and fall
• Living in or traveling to an area where an enterovirus outbreak is occurring
• Exposure to mosquitoes in regions where West Nile virus circulates

It is important to stress that the vast majority of children who catch these common viruses never develop flaccid myelitis. Why a small number do is still an area of active research.

Flaccid myelitis diagnosis

There is no single test that proves flaccid myelitis. Instead, a flaccid myelitis diagnosis is based on a combination of the medical history, a careful physical examination, imaging and laboratory tests. Because the condition can worsen quickly, this assessment is usually done urgently, often in a hospital.

Steps your doctor may use include:

• History and neurological examination. The doctor asks about recent illnesses and the timing of the weakness, then tests muscle strength, muscle tone, reflexes and sensation in each limb. The typical finding is weakness with reduced tone and reduced reflexes, while sensation stays normal.
• Magnetic resonance imaging (MRI) of the spinal cord. MRI uses magnets and radio waves to make detailed pictures of the spine. In flaccid myelitis it often shows a characteristic change in the gray matter, particularly in the front part of the cord where the motor neurons sit. A brain MRI is commonly done at the same time to look for other explanations, such as brainstem involvement.
• Lumbar puncture (spinal tap). A thin needle is used to take a small sample of cerebrospinal fluid, the clear fluid that surrounds the brain and spinal cord. In flaccid myelitis this fluid often shows an increased number of white blood cells, a sign of inflammation.
• Nerve conduction studies and electromyography (EMG). These tests measure how well electrical signals travel along nerves and into muscles. They help distinguish flaccid myelitis from conditions that damage the nerves outside the spinal cord, such as Guillain-Barré syndrome.
• Samples for viral testing. Swabs from the nose and throat, along with stool, blood and spinal fluid samples, are sent to look for enteroviruses, poliovirus, West Nile virus and other possible causes. Public health laboratories are often involved.

Doctors also work to rule out other conditions that can look similar, including Guillain-Barré syndrome, transverse myelitis (inflammation across the whole width of the spinal cord that usually also affects sensation), stroke, spinal cord compression, botulism and certain metabolic disorders. In many countries, suspected cases are reported to public health authorities, which apply a standard case definition based on sudden flaccid limb weakness plus MRI evidence of gray matter involvement in the spinal cord.

Flaccid myelitis treatment options

At present there is no specific medicine that has been proven to cure flaccid myelitis or to reverse the damage to the motor neurons. Flaccid myelitis treatment options therefore focus on supporting the body during the acute illness, trying to limit inflammation where a doctor judges this reasonable, and then helping the person regain as much function as possible through rehabilitation.

Hospital monitoring and supportive care. Because weakness can spread rapidly and can involve the muscles used for breathing and swallowing, people with suspected flaccid myelitis are usually admitted to the hospital. Breathing is watched closely, and some patients need help from a breathing machine (ventilator) for a period. If swallowing is unsafe, feeding may be given through a tube to prevent food or liquid from entering the lungs. Pain is treated, and steps are taken to prevent complications such as pressure sores, blood clots and stiff joints.

Medications. Several treatments have been tried, but none has been shown in rigorous studies to change the outcome. Your doctor may consider:

• Intravenous immunoglobulin (IVIG), a preparation of antibodies given through a vein, which some specialists use in the hope of reducing immune-related damage
• Corticosteroids, anti-inflammatory medicines, which are used cautiously because they may also reduce the body’s ability to fight the virus
• Plasma exchange, a procedure that filters antibodies from the blood, which has been used in selected cases

Antiviral drugs that reliably work against the enteroviruses involved are not currently available. Decisions about these treatments are made case by case by a team that typically includes a pediatric neurologist, a specialist in disorders of the nervous system in children.

Rehabilitation. Rehabilitation is the part of treatment with the clearest benefit for daily function and usually begins as soon as the person is medically stable. It can include:

• Physical therapy to maintain range of motion, strengthen muscles that still work and prevent contractures (permanent tightening of muscles and joints)
• Occupational therapy to relearn everyday tasks such as dressing, eating and writing
• Speech and swallowing therapy if the face or throat muscles are affected
• Braces, splints or mobility aids to support weak limbs
• Electrical stimulation of muscles in some programs, to help maintain muscle bulk

Rehabilitation is often long term and is coordinated by a specialist in physical medicine and rehabilitation. At Acibadem, this ongoing care is provided through the Physical Medicine & Rehabilitation department, working alongside the neurology team.

Surgery. For some people whose weakness does not improve after many months, surgeons may consider a nerve transfer. In this procedure, a healthy, less essential nerve is redirected to power a paralyzed muscle, most often in the arm or shoulder. Tendon transfers, which move a working muscle’s attachment to take over the job of a paralyzed one, may also be discussed. These operations are usually timed carefully, because nerve transfers tend to work best when done within a certain window after the injury, and results vary from person to person.

Living with flaccid myelitis and outlook

The outlook after flaccid myelitis varies widely. Some people regain a good deal of strength over months to years, especially in muscles that were only partly affected. Others are left with lasting weakness in one or more limbs, and a smaller number remain dependent on breathing support. Recovery, when it happens, tends to be slow and gradual, and it is generally greater in the first year, although improvements can continue beyond that with ongoing therapy. Because the condition is rare and relatively newly recognized, long-term studies are still limited, and doctors are cautious about predicting how any one person will do.

Living with lasting weakness can affect many parts of daily life, including school, play, work and mobility. Children may need adjustments at school, assistive devices and regular follow-up with several specialists. Growth can bring new challenges, such as uneven limb length, joint problems or curvature of the spine (scoliosis), which is why long-term monitoring by an orthopedic team is often recommended. Emotional support for the child and family is an important part of care, and many families find it helpful to connect with support organizations for people affected by flaccid myelitis.

Prevention is limited because the exact trigger cannot be predicted. General measures that reduce the spread of the viruses linked to flaccid myelitis include frequent handwashing with soap and water, avoiding close contact with people who are sick, covering coughs and sneezes, cleaning frequently touched surfaces, and protecting against mosquito bites in areas where West Nile virus is present. Keeping up to date with routine vaccinations, including polio vaccination, remains important, although there is currently no vaccine that specifically prevents flaccid myelitis caused by non-polio enteroviruses.

Frequently asked questions

Is flaccid myelitis the same as polio?

No, although the two conditions look alike. Polio is caused specifically by poliovirus and is prevented by the polio vaccine. Flaccid myelitis describes the same kind of damage to the motor neurons of the spinal cord, but it is linked to other viruses, most often non-polio enteroviruses such as EV-D68. Doctors test for poliovirus during a flaccid myelitis diagnosis to be certain it is not the cause.

What are the first flaccid myelitis symptoms parents should watch for?

The earliest sign is usually sudden weakness or limpness in an arm or leg, often within a week or two of a cold-like illness or fever. Some children first complain of neck, back or limb pain, or a parent may notice that the child is not using one arm normally. Facial drooping, a hoarse voice, trouble swallowing or difficulty breathing are also warning signs that need immediate attention.

What causes flaccid myelitis in children?

Flaccid myelitis causes are believed to be mainly viral. Enteroviruses, particularly EV-D68 and EV-A71, are the most strongly linked, and West Nile virus and adenoviruses have also been associated with it. The virus is thought to damage the motor neurons directly or through the immune response it triggers. Why only a very small number of infected children develop weakness is still being studied.

How do doctors confirm a flaccid myelitis diagnosis?

There is no single confirmatory test. Doctors combine the history of sudden limb weakness after a viral illness, a neurological examination showing low muscle tone and reduced reflexes with normal sensation, an MRI of the spinal cord showing gray matter changes, and a spinal fluid sample showing inflammation. Nerve tests and viral testing of throat, stool and blood samples help rule out other conditions.

Are there effective flaccid myelitis treatment options?

There is currently no treatment proven to reverse the nerve damage. Care focuses on hospital support for breathing and swallowing, careful monitoring, and in some cases medicines such as IVIG or steroids, which are used on a case-by-case basis without firm evidence of benefit. Rehabilitation therapy is the mainstay of longer-term treatment, and nerve or tendon transfer surgery may be considered for selected people with persistent weakness.

Can adults get flaccid myelitis?

Yes, although it is much less common than in children. Most reported cases have been in children under the age of ten, but teenagers and adults have also been affected. The symptoms, tests and treatment approach are broadly similar across age groups.

Does flaccid myelitis go away on its own?

The acute inflammation settles over days to weeks, but the weakness it causes often does not fully resolve. Many people recover some strength over months to years, particularly with consistent rehabilitation, while others have lasting weakness in one or more limbs. Because each case is different, doctors avoid making firm predictions early in the illness.

When to see a doctor

Flaccid myelitis is a medical emergency in its early stage because weakness can spread quickly and can affect breathing. Seek emergency care immediately, or call your local emergency number, if you or your child has any of the following, especially within a few weeks of a cold, cough or fever:

• Sudden weakness or limpness in an arm or leg, or a child who suddenly stops using a limb
• Difficulty breathing, shallow or labored breathing, or a weak cough
• Trouble swallowing, drooling or choking on liquids
• Slurred speech or a hoarse, weak voice
• Drooping of the face or eyelids, or difficulty moving the eyes
• Neck weakness, such as an inability to hold the head up
• Severe neck, back or limb pain together with any weakness
• Rapid worsening of any weakness over hours

Even when weakness seems mild, it should be checked the same day, because early hospital assessment allows doctors to monitor breathing, begin testing and start supportive care promptly. Anyone who has had flaccid myelitis should also see their care team if they notice new pain, joint stiffness, changes in posture or a loss of function that had previously improved.