Acute flaccid myelitis
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Syed Hassan A. Kazmi BSc, MD [2]
Synonyms and keywords:; Acute flaccid paralysis, acute flaccid paralysis with anterior myelitis, paralysis with anterior myelitis, AFM, Enterovirus D68-Associated Anterior Myelitis
Overview
Historical Perspective
- In 2014, physicians in California and Colorado (USA) noted an increase in the number of patients presenting with the acute onset of flaccid paralysis and MRI findings consistent with lesions in the gray matter of the spinal cord.
- In 2014, a total of 120 cases were identified in the US and 22 were identified in 2015
- In 2016, 145 cases of AFM were diagnosed across the USA.
Causes
Acute flaccid myelitis (AFM) may be caused by viral infections or environmental toxins. The following viruses are known to be associated with AFM:
- West Nile Virus
- Coxsackievirus
- Adenovirus
- Poliovirus
- Enterovirus 71 (EV 71) and Entervirus D68 (EV 68)
Differentiating Acute Flaccid Myelitis From Other Diseases
The following table differentiates acute flaccid myelitis from other diseases that cause muscle weakness, hypotonia, and flaccid paralysis:
Diseases | History and Physical | Diagnostic tests | Other Findings | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Motor Deficit | Sensory deficit | Cranial nerve Involvement | Autonomic dysfunction | Proximal/Distal/Generalized | Ascending/Descending/Systemic | Unilateral (UL)
or Bilateral (BL) or No Lateralization (NL) |
Onset | Lab or Imaging Findings | Specific test | ||
Adult Botulism | + | - | + | + | Generalized | Descending | BL | Sudden | Toxin test | Blood, Wound, or Stool culture | Diplopia, Hyporeflexia, Hypotonia, possible respiratory paralysis |
Infant Botulism | + | - | + | + | Generalized | Descending | BL | Sudden | Toxin test | Blood, Wound, or Stool culture | Flaccid paralysis (Floppy baby syndrome), possible respiratory paralysis |
Guillian-Barre syndrome | + | - | - | - | Generalized | Ascending | BL | Insidious | CSF: ↑Protein
↓Cells |
Clinical & Lumbar Puncture | Progressive ascending paralysis following infection, possible respiratory paralysis |
Eaton Lambert syndrome | + | - | + | + | Generalized | Systemic | BL | Intermittent | EMG, repetitive nerve stimulation test (RNS) | Voltage gated calcium channel (VGCC) antibody | Diplopia, ptosis, improves with movement (as the day progresses) |
Myasthenia gravis | + | - | + | + | Generalized | Systemic | BL | Intermittent | EMG, Edrophonium test | Ach receptor antibody | Diplopia, ptosis, worsening with movement (as the day progresses) |
Electrolyte disturbance | + | + | - | - | Generalized | Systemic | BL | Insidious | Electrolyte panel | ↓Ca++, ↓Mg++, ↓K+ | Possible arrhythmia |
Organophosphate toxicity | + | + | - | + | Generalized | Ascending | BL | Sudden | Clinical diagnosis: physical exam & history | Clinical suspicion confirmed with RBC AchE activity | History of exposure to insecticide or living in farming environment. with : Diarrhea, Urination, Miosis, Bradycardia, Lacrimation, Emesis, Salivation, Sweating |
Tick paralysis (Dermacentor tick) | + | - | - | - | Generalized | Ascending | BL | Insidious | Clinical diagnosis: physical exam & history | - | History of outdoor activity in Northeastern United States. The tick is often still latched to the patient at presentation (often in head and neck area) |
Tetrodotoxin poisoning | + | - | + | + | Generalized | Systemic | BL | Sudden | Clinical diagnosis: physical exam & dietary history | - | History of consumption of puffer fish species. |
Stroke | +/- | +/- | +/- | +/- | Generalized | Systemic | UL | Sudden | MRI +ve for ischemia or hemorrhage | MRI | Sudden unilateral motor and sensory deficit in a patient with a history of atherosclerotic risk factors (diabetes, hypertension, smoking) or atrial fibrillation. |
Poliomyelitis | + | + | + | +/- | Proximal > Distal | Systemic | BL or UL | Sudden | PCR of CSF | Asymmetric paralysis following a flu-like syndrome. | |
Transverse myelitis | + | + | + | + | Proximal > Distal | Systemic | BL or UL | Sudden | MRI & Lumbar puncture | MRI | History of chronic viral or autoimmune disease (e.g. HIV) |
Neurosyphilis | + | + | - | +/- | Generalized | Systemic | BL | Insidious | MRI & Lumbar puncture | CSF VDRL-specifc
CSF FTA-Ab -sensitive |
History of unprotected sex or multiple sexual partners.
History of genital ulcer (chancre), diffuse maculopapular rash. |
Muscular dystrophy | + | - | - | - | Proximal > Distal | Systemic | BL | Insidious | Genetic testing | Muscle biopsy | Progressive proximal lower limb weakness with calf pseudohypertrophy in early childhood. Gower sign positive. |
Multiple sclerosis exacerbation | + | + | + | + | Generalized | Systemic | NL | Sudden | ↑CSF IgG levels
(monoclonal) |
Clinical assessment and MRI | Blurry vision, urinary incontinence, fatigue |
Amyotrophic lateral sclerosis | + | - | - | - | Generalized | Systemic | BL | Insidious | Normal LP (to rule out DDx) | MRI & LP | Patient initially presents with upper motor neuron deficit (spasticity) followed by lower motor neuron deficit (flaccidity). |
Inflammatory myopathy | + | - | - | - | Proximal > Distal | Systemic | UL or BL | Insidious | Elevated CK & Aldolase | Muscle biopsy | Progressive proximal muscle weakness in 3rd to 5th decade of life. With or without skin manifestations. |
Epidemiology and Demographics
Incidence and Prevalence
USA
- From June 1, 2012 to July 31, 2015, 59 reported cases met the California Department of Public Health (CDPH) case definition of acute flaccid myelitis (AFM), which defines AFM as acute onset of flaccid limb paralysis along with a lesion in the gray matter of the spinal cord.
- Between August and December of 2014, 120 children from 34 US states met the criteria of AFM as outlined by the CDC.
- From August 2014 through October 2018, CDC has received information on a total of 396 confirmed cases of acute flaccid myelitis (AFM) from EV-D68 across the US; most of the cases have occurred in children
- In October 2018, the New York State Department of Health (NYSDOH) confirmed 39 cases of the enterovirus EV-D68 in children across the state which was associated with an increase in number of cases of AFM.
![](/images/e/e7/AFM.jpg)
Risk Factors
The following risk factors increase the risk of development of AFM:
- Pulmonary comorbities (Asthma, COPD)
- Immunocompromised states (Immunosuppressants, organ transplantation, diabetes, systemic autoimmune diseases, hematologic malignancies)
Natural History, Complications and Prognosis
Natural History
- The clinical course of AFM typically consists of three phases:
- Prodormal phase
- Progressive neurological injury phase
- Convalescent phase
Prodormal phase
- A prodromal, often febrile, illness often precedes the onset of neurological deficits in most patients by a median of 5 days.
- The prodormal period consists of respiratory symptoms such as rhinorrhea, cough, or pharyngitis and/or gastrotestinal symptoms such as nausea, vomiting or diarrhea.
- Some patients report clinical improvement in their preceding illness before return of fever accompanied by headaches, stiff neck, or pain in the neck, back, or affected limb around the time of neurological deficit onset
Progressive neurological injury
- The pattern of limb weakness in AFM corresponds to a lower motor neuron lesion and upper extremities are more commonly affected.
- Involvement of cranial nerves points towards lesions in the cranial nerve motor nuclei of the brainstem
- On CSF examination, mild pleocytosis with mildly elevated protein may be seen
- On MRI, confluent, longitudinally extensive gray matter lesions may be seen in spinal cord. This may progress to nerve root enhancement on MRI in 2-3 weeks.
- On electromyography (EMG), reduced recruitment of motor unit potentials (MUPs) and low amplitude of compound muscle action potentials may be seen.
Convalescent phase
- Months after the initial acute neurological illness, patients suffering from AFM may smild improvements with rehabilitation therapies.
- On CSF examination, pleocytosis may resolve and protein remains elevated
- On EMG, fibrillations may be seen
Complications
AFM may lead to the development of following complications:
- Respiratory failure
- Urinary tract infections
- Skin ulcers and traumatic injury (specially in the affected extremity)
- Progressive muscular atrophy
Prognosis
Diagnosis
Diagnostic Criteria
Diagnosis | Criteria |
---|---|
Confirmed |
AND
|
Probable |
AND
|
Symptoms
The following are the symptoms of acute flaccid myelitis:
- Acute onset of flaccid limb paralysis (asymmetric)
- Fever
- Pain in the paralytic limb
- Eyelid drooping
- Difficulty with swallowing or slurred speech
- Cranial nerve abnormalities
- Headache
- Neck pain
- Bowel/bladder changes