Hypotonia in neonates
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Congenital hypotonia is a relatively common diagnosis in the newborn period. It is defined as a subjective decrease of resistance to passive range of motion in a newborn and can be due to a defect at any level of the nervous system.
Causes include (but are not limited to):
|Central (most common)||Hypoxic ischaemic
Chromosomal abnormalities (e.g.Trisomy 21, Prader-Willi syndrome)
Congenital infections (TORCH)
Drug effects (e.g. benzodiazepines)
|Spinal cord||Birth trauma (especially Breech
|Anterior Horn Cell||Spinal Muscular Atrophy
Pompe's disease (acid maltase deficiency)
|Neuromuscular junction||Myasthenia gravis (transient /
|Muscle||Muscular dystrophies (incl. congenital
Congenital myopathies (e.g. central core disease)
|Peripheral nerves||Hereditary motor and sensory neuropathies|
|Metabolic myopathies||Acid maltase deficiency
The first goal in diagnosing the source of neonatal hypotonia is to ascertain if it is central (upper motor neuron) or peripheral (lower motor neuron). Central causes are the most common. This delineation will determine the investigations most likely to yield a diagnosis.
- Any significant family history - affected parents or siblings, consanguinity, stillbirths, childhood deaths
- Maternal disease - diabetes, epilepsy, myotonic dystrophy (may not be recognised)
- Pregnancy and delivery history - drug or teratogen exposure
- Decreased fetal movements
- Abnormal presentation
- Polyhydramnios/ oligohydramnios
- Apgar scores
- Resuscitation requirements
- Cord gases
- History since delivery:
- Respiratory effort
- Ability to feed
- Level of alertness
- Level of spontaneous activity
- Character of cry
A detailed physical examination should be performed, assessing muscle tone, any asymmetry, the infant's strength, deep tendon reflexes (DTR), and any dysmorphic or unusual features.
|Central||Anterior Horn Cell||Nerve||Neuromuscular Junction||Muscle|
||generalised weakness||weakness, distal>proximal||weakness, face/eyes/ bulbar||weakness, proximal>distal, face, EOM|
|normal/ increased DTRs†
||decreased/absent DTRs,||decreased/absent DTRs||normal DTRs||decreased DTRs|
|+/-dysmorphic features, reduced alertness||Often described as alert||+/- arthrogryposis||+/- contractures|
+ At times babies with profound central hypotonia may have absent DTR, therefore absent DTR at least in the first few days of life would not rule out a central cause for the hypotonia
* Note that the presence of profound weakness as well as hypotonia suggests a disorder of the lower motor neuron. A sign of this may be a weak cry. Weakness is uncommon in central hypotonia except in the acute stages.
Arthrogryposis (the fixation of joints at birth) may be associated with neonatal hypotonia, more commonly with lower motor neuron unit or multisystem abnormalities.
Additional clues which may direct to a specific diagnosis:
- Hepatosplenomegaly - storage disorders, congenital infections
- Renal cysts, high forehead, wide fontanelles - Zellweger's syndrome
- Hepatomegaly, retinitis pigmentosa - neonatal adrenoleukodystrophy
- Congenital cataracts, glaucoma - oculocerebrorenal (Lowe) syndrome
- Abnormal odour - metabolic disorders
- Hypopigmentation, undesceded testes - Prader Willi
Examination of the mother is also important in suspected cases of congenital myotonic dystrophy or myasthenia gravis.
Most studies have found that central causes account for 60-80% of cases and that the diagnosis can usually be made by a careful history and examination. However, there may be a mixed picture. Infants with a peripheral cause for their hypotonia may be at increased risk for problems during labour, delivery and resuscitation and develop hypoxic ischaemic encephalopathy.
Further investigation needs to be guided by history and examination:
- If the infant is hypotonic but has a degree of strength, a central cause is most likely and investigations should be directed toward this.
- If the infant is hypotonic and weak a peripheral cause is possible and an early review by the neurology service is warranted.
If after first line investigations the diagnosis is not clear, please consider referral to neurology. There are rapid advances in genetic diagnostic opportunities that may need to be considered and could impact on early management.
- Ultrasound scan in the first instance.
- MRI may be indicated if a structural abnormality of brain development is suspected and to exclude other abnormalities (for example, evidence of HIE)
- EEG: prognostic information as to brain function, useful clinically if seizures suspected
- Genetics review if dysmorphic features, consider molecular karyotype and DNA methylation studies or FISH for Prader-Willi syndrome (if indicated)
- Congenital infection screen
- Metabolic workup
- Neurology services review
- Cervical myelopathies are an infrequent cause of hypotonia. The diagnosis is made by history and examination. Diagnostic studies are of limited value.
- Molecular genetics - CTG repeats (congenital myotonic dystrophy), deletions in SMN gene (spinal muscular atrophy), consideration of Neuromuscular or other gene panel after neurology review.
- Creatine kinase (levels need to be interpreted with caution in the newborn, as levels tend to be high at birth and increase in the first 24 hours, they also increase with acidosis). If elevated in an early sample, repeat after a few days.
- Nerve conduction studies and muscle biopsy (Depending on clinical situation, may be delayed until around 6 months of age as neonatal results are difficult to interpret)
- Fenichel GM. Neonatal Neurology 3rd edition. Churchill Livingston Inc. 1990
- Paro-Panjan D, Neubauer D. Congenital hypotonia: is there an algorithm? Journal of Child Neurology; Jun2004, Vol.19 (6): 439-43
- Prasad AN, Prasad C. The floppy infant: contribution of genetic and metabolic disorders. Brain and Development; Oct 2003, Vol.25(7): 457-76
Did you find this information helpful?
- Date last published: 03 July 2018
- Document type: Clinical Guideline
- Services responsible: Neonatology
- Author(s): Melinda Nolan
- Owner: Newborn Services Clinical Practice Committee
- Editor: Sarah Bellhouse
- Review frequency: 2 years
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