Definition

• Subjective decrease in resistance to passive range of movement 
• Separate from weakness, which refers to lack of muscle strength
• Important to differentiate between central (upper motor neurone), and peripheral (lower motor neurone) hypotonia – may be a mixed picture. See Table 1 
  • central hypotonia is most common (70–80%)
• Hypotonia
  • relatively common finding in newborn period
  • transient in majority of cases
  • if severe/persistent investigate further

Symptoms and signs

• Reduced activity/movement
• Reduced level of consciousness/alertness
• High pitched, weak or fatigable cry
• Increased or reduced respiratory effort
• Feeding difficulties/choking/pooling of secretions
• Seizures/abnormal movements
• Note: Look for syndrome associated dysmorphic features

• Causes of hypotonia in the newborn baby are numerous, not all are listed here
• Benign congenital hypotonia is a diagnosis of exclusion

Central

• Hypoxic ischaemic encephalopathy (HIE)
• Intracranial haemorrhage
• Structural brain malformation
• Chromosomal abnormalities e.g. trisomy 21, Prader-Willi syndrome
• Congenital infection e.g. TORCH
• Acquired infection e.g. Group B Streptococcus
• Endocrine e.g. congenital hypothyroidism
• Metabolic disorders e.g. acid maltase deficiency (Pompe's disease), carnitine deficiency, muccopolysacharidosis, peroxisome biogenesis disorders e.g. Zellweger syndrome
• Drug effects e.g. benzodiazepines

Peripheral

• Spinal cord e.g. birth trauma (especially breech delivery), syringomyelia
• Anterior horn cell e.g. spinal muscular atrophy (SMA)
• Neuromuscular junction e.g. myasthenia gravis, transitory myasthenia
• Peripheral nerves e.g. hereditary motor and sensory neuropathies e.g. Charcot Marie-Tooth disease
• Muscle disorders e.g. muscular dystrophy, congenital myopathy

Family

• Affected parents/siblings 
• Consanguinity
• Previous miscarriage/stillbirth 
• Metabolic/genetic disease
• Premature death

Maternal

• Diabetes
• Infection 
• Medications
• Myotonic dystrophy
• Myasthenia gravis 

Antenatal

• TORCH infections 
• Drug/alcohol exposure 
• Fetal movements 
• Liquor volume

Birth

• Gestational age 
• Delivery complications
• Malpresentation
• Instrumental delivery 
• APGAR score/resuscitation at birth 
• Cord gases 

Neonatal

• Respiratory distress
• Feeding issues 
• Level of alertness 
• Level of spontaneous movement 
• Seizures 
• Hypoglycaemia 
• Weak cry

Mother

• Examine for signs of myotonic dystrophy

Baby

• Full neurological assessment
• Level of alertness 
• Abnormal posture
• Degree of hypotonia 
  • pull to sit – significant head-lag
  • scarf sign
  • shoulder suspension − ‘slipping through hands’
  • ventral suspension
  • frog-leg posture 
• Asymmetry 
• Strength
• Deep tendon reflexes 
• Primitive reflexes
• Gag and suck
• Fasciculations (including tongue)
• Abnormal eye movements
• Ptosis
• Cataracts
• Dysmorphic features/abnormal facies
• Respiratory effort
• Hepatosplenomegaly
• Undescended testicles
• Contractures
• Arthrogryposis

Table 1: Summary of typical findings according to cause

© Auckland District Health Board 

• Weakness uncommon in central hypotonia – except in acute stages
  • points to lower motor neurone disorder
• Clinical findings which may direct to a specific diagnosis:
  
  • hepatosplenomegaly – storage disorders, congenital infections
  • hypopigmentation, undescended testes – Prader-Willi syndrome
  • hepatomegaly, retinitis pigmentosa – neonatal adrenoleukodystrophy
  • renal cysts, high forehead, wide fontanelle – Zellweger syndrome
  • congenital cataracts, glaucoma, proteinuria – oculocerebrorenal (Lowe) syndrome
  • abnormal odour – metabolic disorders

• Guided by detailed history and clinical examination
• If hypotonic with a degree of strength, central cause is most likely
• If hypotonic and weak, peripheral cause is possible. Discuss with neurologist
• Involve relevant specialist team early

• Specific management determined by individual condition and presentation
• Airway and breathing
  
  • may need resuscitation at birth
  • airway positioning/Guedel airway
  • intubation and ongoing respiratory support
  • suction of respiratory secretions
• Feeding
  
  • specialised bottles/teats
  • nasogastric tube feeds
  • early speech and language team involvement (where available) 
• Skin and developmental care 
  
  • regular position changes to avoid pressure sores, reduce risk of contractures and optimise neurodevelopment (see Developmental care guideline)
• Physiotherapy
  
  • refer to neonatal/paediatric physiotherapy (while inpatient)
  • physiotherapist will: 
    
    • advise on specific handling and positioning to optimise neurodevelopmental outcomes 
    • assess for symmetry and risk of joint contractures/positional deformity and advise on management
  • on discharge refer to community paediatric physiotherapy services
• Early involvement of neurologist, and other specialist teams as indicated