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?
The word floppy can be used to mean:
- A decrease in muscle tone (hypotonia)
- A decrease in muscle power (weakness)
- 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 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 paralysed 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 lesion, let us 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 determine which investigations are appropriate based on our central or peripheral causes.
Central hypotonia
1st 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
2nd line to consider
- MRI
- EEG
- Urine sample
- Congenital viral infections
Peripheral hypotonia
1st line to consider
- CK,
- DNA for Muscular Dystrophy
- Genetic testing for SMA
- EDTA for Prader-Willi
- CXR
- Echo
- Microarray CCG
2nd 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 therefor,e some babies will need:
- Resuscitation at birth
- Assistance in maintaining airway
- Ongoing respiratory support
- Regular physiotherapy: stretching aimed at preventing contractures and positioning.
- Occupational therapy: necessary to facilitate activities of daily living
- Vigorous treatment of respiratory infections, including annual influenza vaccination
- Feeding strategies – Nasogastric tube or gastrotomy
- Management of gastro-oesophageal reflux.
- Evaluation and treatment of cardiac dysfunction
- Parental counseling
Later:
- Prevention and correction of scoliosis with orthopaedic input
- Considerations for the ethical appropriateness of CPR in the event of acute respiratory arrest
- Follow up on general development and stimulation of learning.
Please note that, with advances in SMA treatment and potential gene therapy for 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
