Overview
Definition:
Acute flaccid myelitis (AFM) is a rare but serious neurologic condition characterized by a sudden onset of flaccid paralysis in a limb or limbs
It affects the gray matter of the spinal cord, leading to weakness and loss of muscle tone
AFM is often associated with viral infections, particularly enteroviruses.
Epidemiology:
AFM is a non-polio acute flaccid paralysis
Outbreaks have been reported periodically, with peaks occurring every 2 years, particularly in late summer and early fall
Children are disproportionately affected, with most cases occurring in those under 5 years old
The incidence is low, but its impact is significant due to the potential for permanent disability.
Clinical Significance:
AFM poses a significant challenge for pediatricians and neurologists due to its rapid onset, severity, and potential for long-term sequelae including paralysis and respiratory compromise
Accurate and timely diagnosis, particularly through characteristic MRI findings, is crucial for initiating appropriate management and supportive care to improve outcomes
Understanding AFM is vital for DNB and NEET SS aspirants who will encounter these complex cases.
Clinical Presentation
Symptoms:
Sudden onset of asymmetric flaccid weakness in one or more limbs
Loss of muscle tone
Decreased or absent reflexes in affected limbs
Often preceded by a febrile illness, respiratory symptoms (cough, runny nose), or gastrointestinal symptoms (vomiting, diarrhea)
Some patients may report neck pain or back pain
Sensory deficits are less common but can occur.
Signs:
Asymmetric weakness and decreased muscle tone in affected extremities
Diminished or absent deep tendon reflexes
Normal or minimally altered vital signs, though respiratory muscle weakness can lead to hypoxia and hypercapnia
Cranial nerve palsies can occur in some cases.
Diagnostic Criteria:
Diagnostic criteria for AFM generally include: 1
Acute onset of flaccid paralysis/weakness in one or more limbs
2
Spinal cord gray matter involvement on MRI, characterized by lesions predominantly in the gray matter, often involving the anterior or lateral columns
3
Exclusion of other identifiable causes of flaccid paralysis, such as Guillain-Barré syndrome or traumatic spinal cord injury.
Diagnostic Approach
History Taking:
Detailed history of recent illness, including fever, respiratory or gastrointestinal symptoms, and any preceding travel or exposure
Onset and progression of weakness
Presence of pain
Vaccination history (to rule out vaccine-derived polio)
Recent exposure to similar cases.
Physical Examination:
Thorough neurologic examination focusing on motor strength (graded 0-5), muscle tone (flaccid vs
spastic), reflexes (deep tendon and superficial), sensation (light touch, pinprick, proprioception), and cranial nerves
Assess for respiratory muscle strength and function
Assess for bowel and bladder dysfunction.
Investigations:
Spinal cord MRI is the cornerstone for diagnosis: typically shows T2 hyperintensities in the gray matter of the spinal cord, often in a unilateral or asymmetric pattern, affecting anterior or lateral columns
Cerebrospinal fluid (CSF) analysis may show pleocytosis (increased white blood cells), elevated protein, and normal glucose
viral PCR may be positive for enteroviruses, though often negative
Stool and nasopharyngeal/rectal swabs for enterovirus PCR are crucial
Serologic testing for enteroviruses can also be performed
Electromyography (EMG) and nerve conduction studies (NCS) can help differentiate AFM from other neuropathies, showing denervation changes in affected muscles.
Differential Diagnosis:
Guillain-Barré syndrome (GBS) (typically symmetric, involves peripheral nerves, often with sensory involvement), transverse myelitis (often symmetric, involves white matter), spinal cord compression, poliomyelitis (rare due to vaccination), West Nile virus infection, and other viral myelitides.
Management
Initial Management:
Hospitalization is typically required for close monitoring of respiratory status and neurologic progression
Supportive care is paramount
Airway, breathing, circulation, and disability (ABCD) assessment
Prompt consultation with pediatric neurology and infectious diseases specialists.
Medical Management:
There is no specific antiviral treatment for AFM
Management is primarily supportive and aimed at managing symptoms and complications
Intravenous immunoglobulin (IVIG) or plasma exchange have been used, but evidence of efficacy is limited and controversial
they are sometimes considered for patients with rapid progression or severe disease, particularly if a post-infectious inflammatory component is suspected
Steroids are generally not recommended unless other inflammatory causes are strongly suspected, as they may worsen viral infections
Pain management with analgesics is important.
Surgical Management:
Surgical intervention is generally not indicated for AFM itself
However, surgical management may be required for complications such as severe scoliosis or joint contractures that develop due to chronic paralysis, requiring orthopedic or reconstructive procedures.
Supportive Care:
Aggressive respiratory support is critical, including oxygen therapy, non-invasive ventilation (CPAP/BiPAP), or mechanical ventilation if diaphragmatic weakness is significant
Physical and occupational therapy should be initiated early to maintain range of motion, prevent contractures, and promote functional recovery
Bladder and bowel management programs may be necessary
Nutritional support should be provided as needed
Psychological support for the child and family is essential.
Complications
Early Complications:
Respiratory failure due to paralysis of respiratory muscles
Autonomic dysfunction (e.g., labile blood pressure, cardiac arrhythmias)
Urinary tract infections
Pneumonia
Deep vein thrombosis (DVT) and pulmonary embolism (PE) due to immobility
Pressure ulcers.
Late Complications:
Chronic paralysis with significant functional disability
Muscle atrophy
Joint contractures
Scoliosis
Chronic pain
Post-polio syndrome-like symptoms
Psychological sequelae such as depression and anxiety.
Prevention Strategies:
Preventing AFM largely relies on general public health measures to prevent viral infections
This includes good hygiene practices (handwashing), avoiding close contact with sick individuals, and prompt management of viral outbreaks
For enterovirus infections, there is currently no vaccine for the specific serotypes most commonly associated with AFM.
Prognosis
Factors Affecting Prognosis:
Severity of initial paralysis
Extent of spinal cord involvement on MRI
Promptness and comprehensiveness of supportive care and rehabilitation
Age of the patient
Presence of specific viral etiologies
Some patients experience significant recovery of motor function, while others are left with permanent deficits.
Outcomes:
Outcomes vary widely
Some children may regain substantial motor function over months to years, while others may have persistent weakness, paralysis, and functional limitations
A significant proportion of patients experience only partial recovery, necessitating long-term rehabilitation and adaptive strategies.
Follow Up:
Long-term follow-up with pediatric neurology, physical medicine and rehabilitation, and potentially other subspecialties is crucial
This includes regular assessment of motor function, muscle strength, tone, reflexes, and management of complications
Ongoing physical therapy, occupational therapy, and orthopedic monitoring for deformities are essential.
Key Points
Exam Focus:
AFM: sudden onset, asymmetric flaccid paralysis, spinal cord gray matter involvement on MRI
Enteroviruses (e.g., EV-D68) are common etiologies
Management is primarily supportive
Respiratory support is critical.
Clinical Pearls:
Always consider AFM in a child with acute flaccid paralysis, especially during late summer/fall outbreaks
MRI is key for diagnosis, look for asymmetric gray matter lesions
Early and aggressive supportive care, particularly respiratory, is paramount for survival and functional outcome.
Common Mistakes:
Misdiagnosing AFM as GBS due to limb weakness
remember AFM is usually asymmetric and involves gray matter
Delaying respiratory assessment and support
this is the most life-threatening aspect
Underestimating the need for intensive rehabilitation
long-term recovery is often slow and requires multidisciplinary approach.