An approach to the floppy infant

You are a junior doctor doing a rotation in neonates. Your registrar asks you to assess a 2-day-old baby who was found to be hypotonic on their baby check. They ask you about your approach to assessing the “floppy infant”.

Luckily, you have a stepwise approach to answering this question!

Step 1- Definition and terminology

What does the term floppy mean?

1. A decrease in muscle tone (hypotonia)
2. A decrease in muscle power (weakness)
3. Ligamentous laxity and an increased range of joint mobility

What does the term hypotonia mean?

It is defined as “resistance to passive movement around the joint”

It’s assessed in two ways by clinicians

• Phasic tone: assessed by the response of the muscle to a rapid stretch (tendon reflexes)
• Postural tone: measured by the response of the muscle to a sustained low-intensity stretch (maintaining posture against gravity = significant head lag on pull-to-sit, ragdoll posture on ventral suspension, slipping through the hands when the infant is held under their arms).

With that in mind, you go on to start your approach

Step 2 – A focused history

Discuss with mother and review the notes focusing in on specific risk factors that could give you a clue to the diagnosis

• Antenatal history – Reduced fetal movements, polyhydramnios, breech presentation
• Family history – Muscle disease, stillbirth or consanguinity
• Birth History – Labour, delivery, resuscitation, Apgar score and cord gases
• History since delivery- Respiratory effort, feeding history, level of alertness, level of spontaneous activity and character of cry

Step 3 – Examination and clinical clues

As always, your examination should start with a top-to-toe assessment of the baby using an A-E approach. Your neurological examination is specific to the floppy baby.

Some clinical clues that may further help you:-

• Poor swallowing ability as indicated by drooling and oropharyngeal pooling of secretions
• The cry!! Infants with consistent respiratory weakness have a weak cry
• Paradoxical breathing pattern – intercostal muscles paralyzed with intact diaphragm

It is important to determine whether the hypotonia is central (upper motor neuron) or peripheral (lower motor neuron).

TIP- Examine the baby with mum in a familiar environment to increase the likelihood of the baby being alert but not unsettled or crying.

Remember that in the neonatal period, central causes account for two-thirds of all cases, with hypoxic ischaemic encephalopathy being the most common.

Now that you have narrowed down the likely lesio n, let’s consider some aetiologies. It’s time to think back to the corticospinal tract that you learned all those years ago in medical school to help you.

Step 4 – Investigations

So what next? Let us decide which investigations we think are appropriate according to our central or peripheral causes.

Central hypotonia

1 st line to consider

• Serum (Ca, Glucose, U&Es, Mg, PO4, LFTs, VBG, Lactate and ammonia)
• Septic screen
• Plasma AA
• Urine organic acids
• Cranial Ultrasound
• Microarray CCG

2 nd line to consider

• MRI
• EEG
• Urine sample
• Congenital viral infections

Peripheral hypotonia

1 st line to consider

• CK,
• DNA for Muscular Dystrophy
• Genetic testing for SMA
• EDTA for Prader Willi
• CXR
• Echo
• Microarray CCG

2 nd line to consider

• Neurology services for EMG/ NCS, muscle biopsy

Step 5 – Formulating a management plan

Management plans will differ from case to case but should include a multi-disciplinary team approach.

• Hypotonia can cause a loss of airway control and diminished breathing effort therefore some babies will need:
  • Resuscitation at birth
  • Assistance in maintaining airway
  • Ongoing respiratory support
  • Prevention and correction of scoliosis with orthopaedic input
  • Consideration to the ethical appropriateness of & considerations to the ethical appropriateness of CPR in the event of acute respiratory arrest
  • Follow up of general development and stimulation of learning.

  Please note that with advances in the treatment of SMA and potential gene therapy in DMD, early diagnosis is important. Early treatment is recommended for individuals with infantile-onset (Type 1) and pre-symptomatic SMA.

  Selected references

  Ahmed MI, Iqbal M, Hussain N. A structured approach to the assessment of a floppy neonate. J Pediatr Neurosci. 2016;11(1):2-6. doi:10.4103/1817-1745.181250

  Leyenaar J, Camfield P, Camfield C. A schematic approach to hypotonia in infancy. Paediatr Child Health. 2005;10(7):397-400. doi:10.1093/pch/10.7.397

  Author

  “The real baby doc “- junior paeds doc interested in neonates and acute care medicine. Currently, an ex-pat in Melbourne living the Australian dream spending my time swimming, brunching, and beating my partner at chess. View all posts