Paediatric acute weakness

Take home points

• Acute weakness can be easy to miss. Must consider neuromuscular problems consciously
• Small children may appear weak due to pain so look for trauma
• Respiratory insufficiency and aspiration can occur with surprising rapidity
• Reflexes are key
  • Some absent, especially distally: Lower motor neuron dysfunction
  • All present: Muscle dysfunction
  • Increased: Upper motor neuron dysfunction
• Sensory level suggests spinal cord injury and warrants urgent MRI

Presentation

• <3mo: Poor feeding, reduced activity, floppy, 
• Toddlers: Regress milestones, ceasing to crawl/walk
• Pre-school: Ataxia, clumsy, ceasing to walk
• May present with cause i.e. rash of dermatomyositis or obvious tick bite
• May have localised weakness i.e. Miller-Fisher
• Trauma may masquerade as weakness:
  • Shaken baby syndrome may present as lethargic, irritable child with little or no bruising
  • Focal weakness may be due to underlying fracture
  • Emotional/nutritional neglect may present as weakness

ABC

• Airway compromise from bulbar palsy
• Impaired ventilation
  • Mild/moderate impairment can be very subtle but can progress rapidly
  • Consider repeated spirometry if possible
• Circulatory defects indicate autonomic dysfunction i.e. GBS
• Predictors of ICU/HDU admission
  • Bulbar palsy
  • Vital capacity <20mL/kg
  • >30% reduction in vital capacity from baseline
  • Flaccid quadriparesis
  • Rapidly progressive weakness
  • Autonomic cardiovascular instability

Disability

• Peripheral neuromuscular weakness
  • Anxious looking child with paucity of limb movements
• Central weakness
  • Respiratory distress (subtle) and lack of facial features
• Intracranial causes of weakness
  • Obtundation
  • Hypertonic posturing with scissoring of legs due to hip adduction
• Weak infant
  • Frog leg posture with all limbs lying on bed, abducted at hips and flexed at knees

Exposure

• Consider intra-abdominal pathology i.e. intussusception in the weak, floppy infant
• Look for ticks including deep skin folds
• Look for bites/stings
• Rashes of enterovirus or dermatomyositis
• Signs of NAI
• Weight/height/head circumference should be plotted
• Hypoglycaemia can cause focal weakness

History

• If chronic weakness, needs inpatient workup as extensive differential
• Acute on chronic can occur e.g. influenza in Duchenne
• Tick bites, snake bites, toxic exposures
• Pattern of weakness
  • Ascending?
  • Lateralising?
  • Progressive?

• Sudden onset suggests vascular or epileptic event
• Rapid onset suggests toxidrome, venom
• Family Hx and any consanguinity
• Recent infectious illnesses
• Immunisation history including polio vaccination
• Any overseas travel (polio and diphtheria are common causes of weakness in third world)

Detailed examination

• Muscular
  • Proximal > distal
  • Reflexes preserved until very late
  • May have tenderness
  • Positive Gower’s sign (see next slide)
• Neuromuscular junction e.g. Myaesthenia gravis
  • Fatiguability
  • Reflexes preserved

Detailed examination

• LMN lesion
  • Peripheral > proximal
  • Reflexes lost early
• UMN lesion
  • Initial flaccid phase, then hypertonic and hyperreflexic
  • Sensory level may indicate spinal pathology
  • Intracranial problems may have obtundation, speech dysfunction, ataxia and bulbar dysfunction

Gower’s sign

• Child laid on back and encouraged to stand
• Proximal weakness means will roll over and climb up their own legs

Investigations

• FBC
• Electrolyts
• Urea/creatinine
• CK
• Thyroid
• Adrenal tests
• LP
• EMG/ENG testing
• Urgent MRI if suspicious for spinal lesion
• CT/MRI brain if central cause suspected
• CXR for suspected aspiration/respiratory compromise

Guillain-Barre syndrome

• Two main pathological mechanisms: Demyelination and axonal degeneration
• Peaks age 4-9 and males 1.5x more at risk
• <1/100 000 in children
• Associated with Campylobacter, Mycoplasma, EBV, Coxsackie, influenza, echovirus and CMV

• Presentation
  • Weakness, falls, regression and ataxia
  • Muscle pain in early part of illness +- paraesthesiae
  • CN involved in 40-50%
  • Miller-Fisher variant = oculomotor palsies, ataxia and areflexia
  • Usually infectious illness in preceding 2 weeks
  • Classically ascending symmetrical weakness
  • Autonomic dysfunction is common
  • Sensory disturbance (esp. proprioception) does occur

• Usually peaks at 1-2 weeks then recovery over 2 -6 weeks
• Recovery may take up to 18 months
• CSF
  • Isolated protein elevation in 90%. Peaks at 5 weeks
  • 5% will have pleocytosis of approximately 100 cells
• C. jejuni serology positive in 30% and can confirm diagnosis in suspected cases
• Treatment
  • ABC monitoring
  • IVIG/plasma exchange

DDx

• Puffer fish, blue ringed octopus, ciguatera – Descending paralysis. Hx.
• Tick paralysis
• Snake envenomation: Coags
• Spinal cord lesion: Sensory level/mixed upper and lower signs. MRI
• Periodic paralysis: FHx, serum potassium
• Infant botulism: Hx of eating honey, culture stools for Clostridium botulinum and test for botulinum toxin
• Organophosphate poisoning: Hx
• Myaesthenia gravis: Often CN involved, fatiguability, look for antibodies, Tensilon test (edrophonium – prevents Ach breakdown)
• Vasculitis: Check urinalysis and look for autoantibodies
• Myositis: Reflexes preserved, no ophthalmoplegia, dermatomyositis rash, CK, EMG
• Polio, diphtheria, enterovirus: Fever and sore throat (diphtheria), immunisations, travel

Predictors of intubation

• Vital capacity <20mL/kg
• Maximum Pinsp <30cmH20
• Maximum Pexp <40cmH20
• Vt 5mL/kg
• pCO2 >50
• Increasing RR
• Increasing O2 requirement
• Increased use of accessory muscles and paradoxical diaphragm movements

Prognosis

• 85% of children recover completely
• Mortality 2-4%

Tick paralysis

• Ixodes holocyclus
• Toxins inhibit release of ACh from motor end plates
• 5-7 days after bite
• Causes ascending paralysis (like GBS)
• Most often CN palsy
• Can worsen for 48 hours after tick removal
• Risk of myocarditis and autonomic dysfunction (rare)
• Remove whole tick (don’t squeeze as can push toxin in and make sure mouth parts are removed)
  • Best to kill with ether-containing spray (pyrethrum spray best) then remove
  • Can use fine forceps close to skin to gently pull tick away or can try string method
• Treatment is supportive

Infant Botulism

• Caused by release of botulinum toxin from C. botulinum in intestines
• Toxin enters terminal bouton of motor nerve and inhibits ACh-containing vesicles from attaching to cell membrane irreversibly
• Risk factors:
  • Exposure to honey in first 6 months (not recommended under 1yo)
  • Decreased frequency of stools
  • Lack of breastfeeding

• Diagnosis
  • Almost always <6mo
  • Descending paralysis (bulbar palsy first) – Often just weak suck and lack of facial expression
  • Fatiguability but lack of reversibility with edrophonium or neostigmine
  • Absence of fever, normal mental status, normal sensation and normal CSF
  • Stool culture/PCR for C. botulinum
  • EMG is characteristic
  • Need high index of suspicion

• Treatment: Supportive and antitoxin
• Antibiotics not recommended unless secondary infection e.g. pneumonia
  • Can increase toxin release into guts
• Continue NG feeds to promote clearance from gut
• Aminoglycosides worsen the paralysis (like myaesthenia gravis)
• 50% need intubation and ventilation
• Infants seem to recover completely

Food-borne botulism

• Consumption of food with pre-formed toxin
• Associated with canned foods prepared at home
• 1/3 have gastroenteritis symptoms
• Usually 18-36 hours after ingestion
• Can occur at any age
• Descending paralysis

Wound botulism

• Fever, infected wound and subsequent paralysis
• Requires aggressive antibiotic and antitoxin therapy

Spinal cord lesions

• The key is a sensory level but can be difficult in preverbal children and transverse myelitis
• May have mixed upper and lower motor neuron in TM also

Transverse myelitis

• Acute spinal cord inflammation of unclear aetiology
• Rapid onset of lower limb weakness (usually) with altered sensation
• Often neck stiffness, fever, lower back pain or abdominal pain early on
• Sensory level usually mid-thoracic
  • Proprioception and vibriosense usually more preserved
• Bladder and bowel disturbance is common
• Tone usually flaccid early then later UMNL signs
• 60% recover fully within weeks to months
• Urgent MRI shows fusiform oedema
• CSF moderate lymphocytosis and mildly raised protein
• Treatment – Possibly corticosteroids

Tumours

• Usually more gradual onset
• Progressive gait and bladder disturbance with back pain in absence of fever is typical
• May have mixed UMN and LMN signs
• Urgent MRI

AV malformations

• Usually thoracic in origin
• May cause compression or vascular steal from spinal cord
• Usually subacute presentation unless haemorrhage or infarction occurs
• May have cutaneous angioma over region +- bruit
• MRI/MRA is usually required

Epidural abscess

• Rare in children
• Back pain, rigidity, fever, leukocytosis and raised ESR
• MRI required

Tethered cord/diastematomyelia

• Fix cord as child grows
• Usually present with subacute weakness
• May see tuft/pit over sacrum

Myaesthenia gravis

• Transient myaesthenia of newborns
  • Maternal myaesthenia anti-AChR antibodies cross placenta
  • Baby born with fatiguable muscle weakness
  • May be flaccid or just poor feeders
  • Improves within weeks
  • Supportive therapy +- intubation and ventilation/NG feeds
  • No increased risk of MG in baby

• Congenital myaesthenia
  • Not due to autoantibodies
• Acquired myaesthenia gravis
  • 1/300 000 under 15 years; 1% of all myaesthenia cases present in children
  • Ptosis, ophthalmoplegia or bulbar weakness
  • Clue is worsening through day due to fatiguability
  • Neostigmine test is preferred in children (Edrophonium can cause arrhythmias)
    • Atropine given prior to block muscarinic effects
  • EMG is characteristic and obviates need for muscle biopsy
  • AChR antibodies are usually present
  • DO NOT GIVE NEUROMUSCULAR BLOCKERS (can last weeks)
  • DO NOT GIVE AMINOGLYCOSIDES

Poliomyelitis

• Always ask about immunisation
• If unimmunised, ask about contact with infants who have recently received Sabin (oral weakened live poliovirus vaccine) as they may excrete the virus in stools
• Ask travel history
• Fever, sore throat, anorexia, nausea, vomiting, generalised abdo pain, malaise, headache then asymptomatic for 1-2 days, then aseptic meningitis and mild transient bladder paralysis/loss of anal reflex
• May then progress to paralytic polio with patchy asymmetrical lower motor neuron weakness (but can be mixed UMN and LMN) often with bulbar palsy

Bell’s palsy

• 3-10/100 000 in children
• Usually 2 weeks after infectious illness with rapid onset over hours
• Lyme disease associated so serology if been in endemic region
• EBV, mumps and herpes simplex all associated
• Presentation
  • Pain around ipsilateral ear (severe ? VZV), abnormal hearing (hyperacusis), 50% have loss of taste to anterior 2/3 of tongue on one side, hemifacial dysaesthesia due to proprioceptive fibres to facial muscles in the facial nerve
• Diagnosis
  • Look for evidence of trauma including NAI, CNS dysfunction, Aural disorders (Ramsay-Hunt), other cranial nerve involvement, HTN and GBS
  • Forehead involved (sparing = UMNL)
  • If <2 reconsider diagnosis

• Prognosis
  • 60-80% full recovery
  • Average time 7 weeks (up to 7 months)
• Treatment
  • Glucocorticoids recommended for almost all cases if presenting within 72 hours of onset (evidence extrapolated from adults)
  • Aciclovir if vesicular rash evident
  • Protect cornea: Hypromellose drops three times daily and pad eye shut with ocular lubricant at night

Anticholinesterase toxicity

• Organophosphates and carbamates
• Cholinesterase inhibitors with persistent stimulation at motor end plate and subsequent refractory weakness
• Usually cholinergic toxidrome also
• Intermediate syndrome
  • 12hrs-7 days after initial presentation, proximal limb weakness may arise that is unresponsive to atropine or pralidoxime
• Late neurotoxicity
  • 4-21 days after acute exposure with mixed sensory/motor deficit (can be permanent)
• Avoid muscle relaxants as have prolonged effect

Lead and other heavy metals

• Lead, mercury, arsenic can all cause mononeuritis multiplex
• Vincristine/vinblastine and cisplatin can all cause peripheral neuropathy also

Juvenile dermatomyositis

• Systemic vasculitis thought to follow an infection
• Associated with enteroviruses and GAS
• Most common myositis of childhood
• Peak age 6 years
• Usually gradual onset
• Vasculitis can also affect myocardium, cardiac conduction, kidneys, liver, spleen, retina, iris, CNS, lungs

• Rash may occur prior to weakness
  • Malar rash with heliotropic discolouration of eyelids
  • Extensor surfaces of arms/legs/thorax/ankles/buttocks
  • Gottron’s papules over finger joints
  • Weakness often 2 months later
  • Proximal weakness predominates
  • Children may present with hoarse voice or dysphagia due to pharyngeal weakness
  • Affected muscles often tender and swollen

• Diagnosis
  • Raised CK + History
• Complications
  • Calcinosis of muscles, subcut fat and fascia
    • May then become infected
• Treatment
  • Judicious pain relief and referral
  • Sunscreen for rash
  • Immunosuppression
• Prognosis
  • 80% make good recovery

Infectious myositis

• Influenza usually causes widespread myositis
• Strep, Mycoplasma may cause focal myositis with prospect of permanent muscle damage
• CK raised +- rhabdomyolysis/myoglobinuria

Periodic paralyses

• Genetic ion channel disorders leading to acute episodes of weakness lasting from 1 hour up to more than a day
• Often come on after rest, during sleep or following exercise but NEVER during exercise
• Diagnosis is by serum electrolyte measurement during attack or response to metabolic challenge OR gene mutation identification
  • Hypokalaemic variety: Presents in adolescence
  • Hyperkalaemic variety: Early childhood, more frequent attacks. May have normal or elevated K

Somatisation disorders/malingering

• Inconsistent neurological examination
• Child will have knees give way but not fall (requires more strength than just walking as equates to a squat)
• Reflexes will be normal
• Discuss with carer first
• Reassurance is often best method
• Investigate social situation

Bulbar vs. pseudobulbar palsy

• Bulbar = Lower motor neuron lesion of CN IX, X and XII
• Pseudobulbar = Upper motor neuron lesion of CN IX, X and XII

Last Updated on November 10, 2021 by Andrew Crofton