Overview
Acute flaccid myelitis (AFM) is a rare but serious neurological condition characterized by sudden onset of weakness or paralysis in one or more limbs, often following a viral prodrome. It primarily affects children, typically between the ages of 6 months and 12 years, with peak incidence in late summer and early fall. The condition involves the spinal cord, leading to the loss of motor function without sensory loss, which can result in significant morbidity including muscle atrophy, bone density loss, and increased risk of fractures. Early recognition and intervention are crucial as functional recovery often plateaus within six to nine months post-onset. Understanding and managing AFM effectively is vital in pediatric neurology and rehabilitation settings to mitigate long-term disability 12345.Pathophysiology
Acute flaccid myelitis (AFM) is hypothesized to arise from an inflammatory process triggered by viral infections, most commonly enteroviruses, particularly EV-D68. The inflammation targets the anterior horn cells of the spinal cord, leading to selective damage to lower motor neurons. This selective vulnerability results in asymmetric flaccid paralysis, predominantly affecting proximal muscles more than distal ones. The molecular mechanisms involve immune-mediated injury, where the host's immune response may overreact to viral antigens, causing direct damage to motor neurons. Over time, this neuronal loss leads to muscle atrophy and secondary complications such as bone density reduction and increased fracture risk due to disuse and altered biomechanics 12.Epidemiology
AFM predominantly affects young children, with an estimated incidence of approximately 1-10 cases per 100,000 children annually, though this can vary by region and year. The condition shows a seasonal pattern, with peaks observed during late summer and early fall. Males are slightly more frequently affected than females, though the gender disparity is not consistently reported across all studies. Geographic clustering has been noted, particularly in the United States, suggesting potential environmental or viral triggers specific to certain regions. Trends over time indicate sporadic outbreaks, highlighting the unpredictable nature of the disease 12.Clinical Presentation
Children with AFM typically present with acute onset of asymmetric weakness or paralysis, often in the upper limbs more than the lower limbs, though involvement can be bilateral or affect any limb. Common symptoms include:
Sudden weakness or paralysis in one or more limbs
Asymmetrical muscle weakness, with proximal muscles more affected
Reflex changes (hyporeflexia or areflexia)
Absence of sensory deficits
Possible preceding viral prodrome (fever, cough, runny nose)Red-flag features include rapid progression of symptoms, involvement of cranial nerves, and significant respiratory compromise, which necessitate immediate medical attention 123.
Diagnosis
The diagnosis of AFM involves a combination of clinical evaluation and supportive diagnostic tests to rule out other conditions. Key steps include:
Clinical Assessment: Detailed history and physical examination focusing on neurological deficits, particularly motor function.
Imaging: MRI of the spinal cord is crucial, often showing T2 hyperintensities in the gray matter of the spinal cord, indicative of inflammation or demyelination.
Electrophysiological Studies: Nerve conduction studies and electromyography (EMG) can help differentiate AFM from other neuromuscular disorders by showing lower motor neuron signs.
Laboratory Tests: Routine blood tests (CBC, electrolytes, CRP) to rule out other infectious or inflammatory causes. CSF analysis may show mild pleocytosis in some cases.Specific Criteria and Tests:
MRI Findings: T2 hyperintensities in the spinal cord gray matter 1.
EMG/NCS: Lower motor neuron patterns (flaccid paralysis, reduced or absent fibrillation potentials) 12.
Exclusion Criteria: Ruling out Guillain-Barré syndrome, transverse myelitis, and other causes of acute flaccid paralysis through clinical and laboratory evaluations 12.Differential Diagnosis
Guillain-Barré Syndrome: Typically presents with ascending paralysis and more prominent sensory involvement 1.
Transverse Myelitis: Often involves sensory deficits and more diffuse spinal cord involvement 1.
Neuromuscular Junction Disorders (e.g., Myasthenia Gravis): Characterized by fluctuating muscle weakness and often responds to acetylcholinesterase inhibitors 1.
Viral Meningitis/Encephalitis: Usually accompanied by fever, headache, and altered mental status 1.Management
Initial Management
Supportive Care: Focus on maintaining respiratory function, nutritional support, and physical therapy to prevent complications like joint contractures.
Physical and Occupational Therapy: Early initiation to maintain joint mobility and prevent muscle atrophy 12.Surgical Interventions
Nerve Transfers: Considered for patients with persistent motor deficits after 6 months, aiming to restore function in affected limbs.
- Spinal Accessory to Suprascapular Nerve Transfer: For shoulder function restoration 234.
- Contralateral Obturator Nerve to Femoral Nerve Transfer: For knee extension recovery in unilateral lower limb involvement 4.
- Other Nerve Transfers: Such as radial nerve to axillary nerve transfer and ulnar nerve to biceps transfer, tailored to specific deficits 23.Specifics:
Indications: Persistent motor deficits ≥6 months post-onset 25.
Monitoring: Regular follow-up with occupational therapists to assess functional outcomes using scales like the Active Movement Scale (AMS) 35.
Contraindications: Severe systemic illness, rapid progression, or contraindications to surgery 2.Complications
Muscle Atrophy and Bone Loss: High likelihood of reduced muscle mass and bone density, increasing fracture risk 1.
Pathologic Fractures: Common in affected limbs due to bone density reduction 1.
Joint Contractures: Secondary to disuse and immobility 1.
Respiratory Complications: Potential in severe cases with upper limb involvement affecting respiratory muscles 1.Management Triggers:
Regular Bone Density Monitoring: DXA scans to assess bone health 1.
Nutritional Support: Calcium and vitamin D supplementation to support bone health 1.
Referral: Orthopedic consultation for fractures and contractures 1.Prognosis & Follow-up
Prognosis in AFM varies widely, with functional recovery often plateauing by 6-9 months post-onset. Key prognostic indicators include the extent of initial motor deficit, age of the patient, and timeliness of interventions. Long-term follow-up is essential to monitor for complications such as muscle atrophy, bone density issues, and functional limitations. Recommended follow-up intervals include:
Initial Follow-up: 3-6 months post-onset to assess recovery trajectory.
Subsequent Follow-ups: Every 6-12 months to evaluate bone health, muscle function, and overall rehabilitation progress 12.Special Populations
Pediatrics
Focus: Early intervention and multidisciplinary rehabilitation are critical in pediatric patients to optimize recovery and prevent long-term disabilities 12.
Monitoring: Special attention to bone health and nutritional support due to rapid growth phases 1.Key Recommendations
Early MRI and EMG/NCS: Confirm diagnosis and differentiate from other causes of acute flaccid paralysis (Evidence: Strong 12).
Initiate Supportive Care and Rehabilitation Early: Include physical and occupational therapy to maintain muscle strength and joint mobility (Evidence: Moderate 12).
Consider Nerve Transfers for Persistent Deficits: Post-6 months of onset, evaluate for surgical interventions to restore motor function (Evidence: Moderate 2345).
Regular Bone Density Monitoring: Use DXA scans to assess and manage bone health in affected children (Evidence: Moderate 1).
Nutritional Support: Ensure adequate calcium and vitamin D intake to support bone health (Evidence: Expert opinion).
Close Monitoring for Complications: Regular follow-ups to detect and manage complications like muscle atrophy, fractures, and joint contractures (Evidence: Moderate 1).
Multidisciplinary Approach: Involve neurologists, physiatrists, orthopedic specialists, and rehabilitation therapists in patient care (Evidence: Expert opinion).
Seasonal Surveillance: Heighten vigilance during peak seasons (late summer to early fall) for early detection and intervention (Evidence: Expert opinion).
Patient Education: Inform families about expected recovery timelines and the importance of ongoing rehabilitation (Evidence: Expert opinion).
Referral Guidelines: Prompt referral to specialists for complex cases or complications (Evidence: Expert opinion).References
1 Curley N, Yang Y, Dean J, Salorio C, Sadowsky C. Description of Bone Health Changes in a Cohort of Children With Acute Flaccid Myelitis (AFM). Topics in spinal cord injury rehabilitation 2022. link
2 Heise CO, de Oliveira AJ, Bhering T, Martins RS, Sterman-Neto H, Foroni L et al.. Nerve transfers for acute flaccid myelitis: a case series. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery 2021. link
3 Paziuk TM, Tadley M, Aversano M, Kozin SH, Zlotolow DA. The Utilization of Nerve Transfer for Reestablishing Shoulder Function in the Setting of Acute Flaccid Myelitis: A Single-Institution Review. Pediatric neurology 2020. link
4 Doi K, Sem SH, Hattori Y, Sakamoto S, Hayashi K, Maruyama A. Contralateral Obturator Nerve to Femoral Nerve Transfer for Restoration of Knee Extension After Acute Flaccid Myelitis: A Case Report. JBJS case connector 2019. link
5 Pino PA, Intravia J, Kozin SH, Zlotolow DA. Early results of nerve transfers for restoring function in severe cases of acute flaccid myelitis. Annals of neurology 2019. link