Acute Flaccid Myelitis (AFM) is an inflammatory condition of the spinal cord that causes sudden muscle weakness. It is a rare condition with fewer than a million new patients recorded worldwide every year, mainly children.

The median age of AFM patients reported in 2014 was 7.1 years (with an age range of 4.8 – 12.1 years), but it can affect adults as well. AFM causes damage to the gray matter of the spinal cord, where the cell bodies of the neurons are located. This affects the ability to pass signals between the central and peripheral nervous system.

AFM Signs and Symptoms

The symptoms of AFM are similar to those of poliomyelitis. Children affected by AFM experience a sudden onset of muscle weakness. It is advised that parents who notice a sudden loss of muscle strength and tone in children seek medical attention, as this is a typical symptom of EFM. The motor and sensory symptoms associated with AFM are usually scattered and asymmetric.

The first distinctive signs of AFM present after an initial period of flu-like symptoms that last several days. These include respiratory and/or gastrointestinal symptoms. The patient then presents with acute muscle weakness in the extremities, as well as neck stiffness and pain. Cranial nerve abnormalities and headache are commonly present.

The muscles affected by AFM include:

• arm and leg muscles,
• muscles of the face and mouth,
• eye muscles

Along with acute-onset muscle weakness, some patients report pain, but this is not typical. The most common symptoms in children developing AFM include:

• sudden weakness of muscles in the arms or legs
• loss of reflexes
• facial muscle droop including drooping eyelids
• difficulty in moving the eyes
• difficulty in swallowing
• slurred speech

Other symptoms include tingling and numbness in the arms and legs, as well difficulty in passing urine. The severity of the symptoms varies depending on the localization and number of damaged neurons; and it could lead to complete paralysis in the most severe cases. AFM is most dangerous when it affects the muscles involved in breathing, as this may cause respiratory failure. When AFM is suspected, precautions should be taken to ensure that the patient’s airway is protected.

If the AFM is identified as following a viral infection, the time that elapses between the infection and the first symptoms will depend on the type of virus. As AFM is considered a rare disease, the symptoms also vary on a case-to-case basis.

AFM Differential Diagnosis

Since the symptoms of AFM are similar to those of some other viral infections and neurodegenerative disorders, it is important to differentiate it from the following disorders at the time of diagnosis:

• Guillain-Barre syndrome (GBS)
• transverse myelitis
• acute disseminated encephalomyelitis (ADEM)
• spinal cord infarction
• early “spinal shock”

In contrast to GBS, where the symptoms presented are usually symmetrical (e.g. paralysis that affects both upper limbs), the signs of AFM are typically scattered and asymmetrical. An MRI scan, as well as additional tests as indicated, should be run in order to present the right diagnosis.

Examples of laboratory testing recommendations for patients with suspected AFM:

• testing the cerebrospinal fluid (CSF),
• nerve conduction velocity (NCV) tests,
• electromyography (EMG) to test muscle response to stimuli from nerve cells,
• Respiratory PCR panel
• enterovirus PCR
• West Nile Virus IgG and IgM in serum
• EBV antibodies
• Lyme serology (where applicable)

Further Reading

• All Acute Flaccid Myelitis Content
• What is Acute Flaccid Myelitis?
• Acute Flaccid Myelitis Treatment
• Acute Flaccid Myelitis Causes and Diagnosis