Neonatal Hypotonia (Floppy Baby)

Baby with low muscle tone

Aetiology

Central

  • Hypoxic ischaemic encephalopathy
  • Intracranial haemorrhage
  • Cerebral malformations
  • Chromosomal abnormalities (e.g. trisomy 21, Prader-Willi syndrome)
  • Congenital infections (TORCH)
  • Acquired infections
  • Peroxisomal disorders
  • Drug effects (e.g. benzodiazepines)

Spinal cord

  • Birth trauma (especially breech delivery)
  • Syringomyelia

Anterior horn cell

  • Spinal muscular atrophy
  • Pompe's disease (acid maltase deficiency)

Neuromuscular junction

  • Myasthenia gravis (transient/congenital)
  • Infantile botulism

Muscle

  • Muscular dystrophies (incuding congenital myotonic dystrophy)
  • Congenital myopathies (e.g. central core disease)

Peripheral nerves

  • Hereditary motor and sensory neuropathies

Metabolic myopathies

  • Acid maltasedeficiency
  • Carnitine deficiency
  • Cytochrome-c-oxidase deficiency

Clinical presentation

  • 'Rag doll'
  • Lack of head control
  • Increased range of movement
  • 'Frog legged'
  • 'Feel like they'll fall out your grasp'
  • Possibly breathing difficulties
notion image

Examination findings

Central
  • Normal strength
  • Normal/increased DTRs
  • +/- seizures
  • +/- dysmorphic features, reduced alertness
Anterior horn cell
  • Generalised weakness
  • Decreased/absent DTRs
  • Fasciculations
  • Often described as alert
Neuromuscular junction
  • Weakness, face/eyes/bulbar
  • Normal DTRs
  • No fasiculations
  • +/- arthrogryposis +/- contractures
Muscle
  • Weakness - proximal > distal, face, EOM
  • Decreased DTRs
Nerve
  • Weakness distal > proximal
  • Decreased/absent DTRs
  • +/- fasciculations

Investigations

Bloods

  • Genetics - NGS
  • Metabolic
  • Congenital infection screening
  • Creatinine kinase

Neurology review

  • EEG
  • EMG (after 6 months)

Imaging

  • Cranial USS
  • MRI

Management

  • Early intervention - respiratory and feeding support, physiotherapy, occupational therapy, patient involvement
  • Regular review of growth and development - clinic followup, health visitor and GP communication
  • Some specific management may be available depending on cause e.g. RNA targeted therapy for spinal muscular atrophy
    • Early diagnosis is key as there is often a critical window for treatment (e.g. in PKU, spinal muscular atrophy)