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Acute flaccid myelitis, a rare polio-like illness in children that needs a fast response.

Sudden limb weakness after a viral illness is uncommon, but it is a paediatric emergency. Early recognition, MRI of the spinal cord and specialist rehabilitation change the long-term outcome.

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A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against UKHSA surveillance data, WHO polio-like illness case definitions and the US AFM Task Force literature.

  • 03

    Current for 2026

    Reflects current UK surveillance, MRI grey-matter reporting standards and rehabilitation pathways after paediatric AFM.

Key facts

AFM at a glance.

The essentials, in plain English - what AFM is, why it happens, and what a good diagnostic and treatment pathway looks like in the UK.

  • What it is

    A rare acute paralytic illness affecting the spinal cord grey matter, usually in children, often preceded by a viral respiratory or febrile illness.

  • The likely trigger

    Non-polio enteroviruses, especially enterovirus D68 (EV-D68) and enterovirus A71 (EV-A71), account for most confirmed clusters.

  • Classic pattern

    Sudden asymmetric limb weakness with hyporeflexia and hypotonia, often with cranial nerve, bulbar or respiratory involvement.

  • Diagnosis hinges on

    MRI of the spinal cord showing T2-hyperintense signal largely confined to the anterior grey matter, plus CSF pleocytosis.

  • Not the same as GBS

    Guillain-Barre syndrome is typically ascending, symmetric and demyelinating. AFM is asymmetric, grey-matter and lower motor neurone.

  • Recovery

    Around 60 per cent make a partial recovery, 30 per cent are left with meaningful weakness and about 10 per cent have severe residual disability.

Why this guide matters

Rare, but time-critical.

AFM is uncommon and often frightening. The three points below shape everything else on this page.

  • Weakness after a virus is a red flag

    Any new limb weakness in a child after a febrile or viral illness deserves urgent paediatric review, not watchful waiting at home.

  • MRI and CSF drive the diagnosis

    Spinal cord MRI showing anterior grey-matter signal, together with CSF pleocytosis and virology, is what confirms AFM and separates it from mimics.

  • Rehabilitation shapes the outcome

    There is no magic drug. Long-term, structured neuro-rehabilitation is the single biggest driver of recovery of function.

How the diagnosis is made

From first symptoms to a confirmed diagnosis.

The steps a UK paediatric team will normally follow, in order - so families know what to expect and why each test matters.

  1. 01

    Recognising

    Rapid paediatric assessment

    Any child with sudden limb weakness after a febrile or viral illness should be seen urgently by paediatrics with neurology on call.

  2. 02

    Recognising

    Airway, breathing and bulbar check

    Weak cough, drooling, nasal speech, difficulty swallowing or shallow breathing all point to bulbar and respiratory involvement.

  3. 03

    Recognising

    Neurological examination

    Documented asymmetric weakness with reduced tone, reduced or absent reflexes and preserved sensation is highly suggestive of an anterior horn cell process.

  4. 04

    Confirming

    MRI of the spinal cord

    T2-hyperintense signal largely confined to the central grey matter of the cord, sometimes extending over multiple segments, is close to pathognomonic in the right context.

  5. 05

    Confirming

    Lumbar puncture and CSF analysis

    A mild-to-moderate lymphocytic pleocytosis is typical. CSF is sent for enterovirus and other viral PCR.

  6. 06

    Confirming

    Virology from multiple sites

    Nasopharyngeal or throat swab, stool samples and CSF are sent for enterovirus PCR, including EV-D68 and EV-A71 typing.

  7. 07

    Characterising

    EMG and nerve conduction studies

    Nerve conduction and EMG help confirm a motor axonal or anterior horn cell pattern and separate AFM from demyelinating disease such as GBS.

Typical timeline: from A&E presentation to a working diagnosis in hours, not days.

Symptoms

What AFM actually looks like.

The pattern that separates AFM from more common childhood infections - and the features that mean it is time to call for help.

  • Sudden limb weakness

    One or more limbs become weak or floppy over hours to a few days, often after an apparently minor viral illness.

  • Asymmetric pattern

    Weakness is usually markedly asymmetric, unlike the more symmetric ascending pattern seen in classical Guillain-Barre syndrome.

  • Hypotonia and hyporeflexia

    The affected limbs are floppy with reduced or absent tendon reflexes, reflecting an anterior horn cell (lower motor neurone) process.

  • Cranial nerve involvement

    Facial droop, difficulty moving the eyes or a weak swallow can appear when the brainstem motor nuclei are affected.

  • Bulbar symptoms

    Slurred speech, nasal voice, pooling saliva, choking on feeds and difficulty swallowing are important warning signs.

  • Respiratory involvement

    A weak cough, shallow breathing or rising respiratory rate can herald diaphragmatic weakness and the need for ventilatory support.

  • Preceding febrile illness

    Most children have had a viral respiratory illness or fever in the days to two weeks before the weakness appears.

  • Red flag - rapid deterioration

    Progression to multi-limb weakness, bulbar signs or respiratory difficulty is a paediatric emergency needing intensive care assessment.

Treatment

How AFM is treated in the UK.

Intensive supportive care first, then immunomodulation where appropriate, and finally the long, patient work of rehabilitation.

  • Intensive supportive care

    Close monitoring on a paediatric ward or PICU, with airway protection, non-invasive ventilation or intubation as needed if respiratory muscles are affected.

  • Respiratory support

    From simple oxygen and cough assist to non-invasive ventilation and, in severe cases, mechanical ventilation via endotracheal tube or tracheostomy.

  • Intravenous immunoglobulin

    IVIg is commonly given, especially early, on the basis of expert consensus and biological plausibility, although randomised evidence is limited.

  • Corticosteroids

    Their role is debated. Some centres use them for suspected inflammatory or oedematous cord involvement, weighing benefit against theoretical infection risk.

  • Plasma exchange (PLEX)

    Considered in severe or rapidly progressive cases, or where an antibody-mediated process cannot be excluded, in specialist centres.

  • Physiotherapy and OT

    Early and sustained physiotherapy, occupational therapy and splinting help maintain range of movement, prevent contractures and support recovery.

  • Neuro-rehabilitation programme

    Structured inpatient and community neuro-rehabilitation over months to years, often at a specialist paediatric centre.

  • Nerve and tendon transfer surgery

    Selected children with persistent focal weakness may benefit from reconstructive surgery in specialist centres once recovery has plateaued.

What this guide is based on

The sources behind every claim on this page.

UK surveillance guidance, WHO case definitions and international clinician resources, current at the time of last review.

Key references

Guidelines and surveillance we relied on.

A quiet reminder

This guide is for information, not medical advice.

Any child with new limb weakness should be assessed urgently by a doctor. If you are worried about breathing or swallowing, call 999 or attend A&E.

  • UK Health Security Agency (UKHSA). Acute flaccid paralysis / acute flaccid myelitis surveillance guidance.

  • World Health Organization. Case definitions for acute flaccid paralysis (AFP) and vaccine-derived poliovirus surveillance.

  • US Centers for Disease Control and Prevention. Acute Flaccid Myelitis clinician resources and AFM Task Force reports.

  • Royal College of Paediatrics and Child Health (RCPCH). Guidance on acute paediatric neurological presentations.

  • Peer-reviewed literature on enterovirus D68, EV-A71 and non-polio enterovirus outbreaks.

Red flags

When to act immediately.

AFM is uncommon, but every feature below should trigger urgent hospital review, not a wait-and-see approach.

  • Any new limb weakness in a child

    Sudden weakness of an arm or a leg after a viral illness always warrants urgent paediatric assessment, even when the child otherwise looks well.

  • Bulbar symptoms

    Drooling, choking on feeds, a weak cry or difficulty swallowing suggest brainstem involvement and need immediate hospital review.

  • Breathing difficulty

    Shallow breathing, rising respiratory rate or a weak cough can precede respiratory failure. Call 999 or go straight to A&E.

  • Rapid neurological progression

    Weakness spreading from one limb to others over hours needs urgent transfer to a centre with paediatric neurology and intensive care.

  • Altered consciousness or seizures

    These point to wider central nervous system involvement, such as encephalitis, and change the differential and the treatment.

  • Suspected transverse myelitis or MS

    Sensory levels, bladder involvement or optic symptoms suggest transverse myelitis or a demyelinating illness rather than isolated AFM.

  • Recent travel or unusual exposure

    Travel to areas with circulating polio or vaccine-derived poliovirus, or contact with unwell travellers, must be flagged early to public health.

  • Deterioration after apparent recovery

    Any second dip in strength or breathing after initial improvement should trigger urgent reassessment.

  • Family concern that "something is wrong"

    Parental instinct in a previously well child matters. If a parent feels their child is not right, they should be believed and reviewed.

Living with it

After the acute illness, the long recovery.

Four things that make the biggest difference for families in the months and years after AFM - rehab, school, family support and consistent specialist follow-up.

A quiet reminder

Small, steady gains add up over years.

Recovery from AFM rarely looks like a straight line. Families who keep going with rehabilitation over the long term usually see the best functional outcomes.

  1. 01 Rehab

    The work is long, not linear

    Recovery from AFM is measured in months and years, with plateaus and setbacks. A structured neuro-rehab plan matters more than any single treatment.

  2. 02 School

    Plan reintegration early

    A phased return to school with an EHCP or care plan protects both learning and confidence, especially when weakness or fatigue persists.

  3. 03 Family

    Look after the whole family

    Parents, siblings and carers need support too. Peer groups, psychology input and respite can protect the family system through a long recovery.

  4. 04 Follow-up

    Stay connected to specialists

    Regular follow-up with paediatric neurology, respiratory, orthopaedics and rehab keeps small problems small and picks up late complications early.

Frequently asked

Everything families ask about AFM.

Quick answers on causes, diagnosis, treatment and the long-term outlook.

  • What is acute flaccid myelitis?

    Acute flaccid myelitis (AFM) is a rare but serious neurological illness that mainly affects children. It causes sudden weakness and floppiness in one or more limbs, often after a viral infection, because inflammation damages the anterior horn cells of the spinal cord.

  • What causes AFM?

    Most cases are linked to non-polio enteroviruses, especially enterovirus D68 (EV-D68) and enterovirus A71 (EV-A71). Other viruses and, historically, poliovirus can cause a similar picture. In many cases the exact trigger is never identified even after extensive testing.

  • How is AFM different from Guillain-Barre syndrome?

    GBS is usually a symmetric ascending weakness caused by an immune attack on peripheral nerves, with reduced reflexes and often sensory symptoms. AFM is typically an asymmetric weakness affecting the anterior horn cells of the spinal cord, with a very characteristic MRI pattern of grey-matter T2 signal.

  • How is AFM diagnosed?

    Diagnosis is made by a paediatric neurology team using a combination of the clinical picture, MRI of the spinal cord (looking for T2 signal in the grey matter), CSF analysis after lumbar puncture and virology on throat swab, stool and CSF. EMG and nerve conduction studies help confirm a motor neurone pattern.

  • What treatments are available?

    There is no single proven cure. Care focuses on protecting the airway and breathing, intravenous immunoglobulin (IVIg), sometimes corticosteroids or plasma exchange in severe cases, and above all long-term rehabilitation with physiotherapy, occupational therapy and, where useful, reconstructive surgery.

  • What is the long-term outlook?

    Outcomes vary. Broadly, around 60 per cent of children make a partial recovery, about 30 per cent are left with meaningful residual weakness and roughly 10 per cent have severe long-term disability. Early recognition, intensive care and sustained rehabilitation improve the chances of a better outcome.

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