Assessing the floppy baby

March 24, 2024
Neonatology
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Floppy can be used to describe:

Decreased muscle tone (hypotonia)
Decreased muscle power (weakness)
Ligamentous laxity and increased range of joint mobility

There are a wide range of causes of “floppiness” in a baby which present in different ways and will have different examination findings.

Hypotonia:

Congenital hypotonia is defined as a subjective decrease of resistance to passive range of motion around the joint in a newborn.

Causes of Hypotonia

Central causes are most common cause of congenital hypotonia, accounting for 60-80%.

Central:

Hypoxic Ischaemic Encephalopathy (HIE)
Intracranial Haemorrhage (ICH)
Cerebral malformations
Chromosomal malformations, e.g. Trisomy 21 (T21) / Prader Willi
Congenital infections, TORCH (or SCORTCH)
Acquired infections (sepsis)
Peroxisomal disorders, e.g. neonatal adrenoleukodystrophy, Zellwegers syndrome
Iatrogenic / poisoning, e.g. benzodiazepines / atracurium
Congenital Hypothyroidism
Hypoglycaemia
Inborn errors of metabolism, e.g. mucopolysaccharidoses, amino acidurias, organic acidurias, lipidoses, glycogen storage disease, Menkes syndrome

Spinal Cord:

Birth trauma, e.g. breech delivery or traumatic forceps delivery
Syringomyelia

Anterior Horn Cell:

Spinal Muscular Atrophy (SMA)
Pompe’s Disease

Neuromuscular Junction:

Congenital Myasthenia Gravis (MG)
Infant botulism

Muscle:

Muscular dystrophies including congenital myotonic dystrophy
Congenital myopathies

Peripheral nerves:

Hereditary motor and sensory neuropathies
Congenital hypomyelination

Metabolic Myopathies

Acid maltase deficiency
Carnitine deficiency
Cytochrome – C – oxidase deficiency

History

Antenatal History

Ask about reduced foetal movements – this can be a common finding in mothers of babies with SMA. It will be particulaly noticeable to them if it is their second baby and their first baby was not hypotonic.
Ask about if fluid levels during pregnancy. Were they told there was too much fluid? (polyhydramnios). This can be associated with a few different congenital malformations but in the context of hyotonia it is associated with SMA
Was the baby breech? If so were they born vaginally? This makes birth trauma more likely, which is associated with HIE.

Family History

Is the a family history of weak muscles or neurological disease?
Are there any maternal medical problems? e.g. maternal diabetes puts the baby at risk of hypoglycaemia, in maternal myasthenia gravis antibodies afainst the acetylcholine receptor esterase can cross the placenta and cause congenital MG, mytonic dystrophy is inherited with anticipation which means that as it is inherited down generations the seveirty increases.
Is there a history of miscarriages or still births? This would be more likely if there is an inborn error of metabolism, chromosomal disorders or SMA.
Are the parents consanguinous? This can be an awkward question to ask sometimes but get used to squeezing it in to your paediatric history as this has important connotations for both your differential diagnoses and for future family planning for the parents. I normally ask “are you related to your spouse in any way except by marriage?”

Birth History

How long was the labour?
Were there any risk factors for sepsis?
- Prolonged rupture of membranes > 24 hours in a term baby or > 18 hours in a preterm baby
- Maternal sepsis
- History of group B streptococcus (GBS) grown on a high vaginal swab (HVS) or in a urine sample from mum or is there a history of GBS sepsis in a previous baby
- Prematurity
Were there any signs of foetal distress or foetal compromise on the CTG?
What were the APGAR signs?
Did the baby need resuscitating? If so, were they intubated and admitted to NICU? Were they cooled?
Were the cord gases poor? (cord gases are venous and arterial blood sampled from the umbilical cord after birth and give you a pH, base excess, bicarbonate, pC02 and sometimes a lactate. If the pH is low it tells you the baby was under a lot of physiological stress at the time of delivery and is at a higher risk for HIE. All neonatal units will have their own guideline to follow for managing poor cord gases but as a rule if the pH is < 7 the baby needs to be admitted to NICU for monitoring and possibly therapeutic cooling.)

*parents may not know the answers to all of these questions but you should be able to find them in the maternity notes.

Postnatal History

Ask about respiratory effort since birth. Respiratory distress is an important sign and could mean many things.
- Increased work of breathing with grunting and tachypnoea could be due to sepsis, hypoglycaemia or acidosis due to an inborn error of metabolism.
- Paradoxical breathing (when the chest moves inwards during inhalation and the abdomen is pushed out, and the abdomen is then sucked in during exhalation). This occurs due to intercostal muscle weakness with preserved diaphragmatic function and therefore is a sign in peripheral hypotonia such as SMA.
Take a good feeding history. How is the baby latching and feeding? With Congenital MG repetitive movements tire the muscles so they may become tired after a few sucks and stop feeding. With encephalopathies they may have lost some primitive reflexes that allow them to root, latch and suck and therefore will be feeding very poorly.
What is the babies consciousness level and level of activity?

Character of cry – babies with SMA have a weak cry, septic babies will have a shrill high pitched cry and may be inconsolable

Examination:

It is important to examine thoroughly top to toe to help you narrow down your list of differentials.

Start by looking from the end of the bed at the babies face for any dysmorphic features and also looking at their general level of activity and posture.

Inspection

See if you can list the dysmorphic facies and other signs you may notice from the end of the bed, associated with the following conditions / syndromes that cause hypotonia. Then click on the drop down button to reveal the answers

Trisomy 21

Flat nasal bridge
Protruding tongue
Epicanthic folds
Upslanting palpebral fissures
Low set ears
Single palmar crease
Sandal gap

Image from Punekar News

Zellwegers Syndrome

High forehead
Wide fontanelles
Midface hypoplasia
Epicanthic folds

Image from Wikipedia

Prader Willi Syndrome

*Children with Prader Willi syndrome are well known to have insatiable appetites and are often overweight in childhood and adolescence but in infancy they are poor feeders, are often small for gestational age and have very poor tone

Fair hair and skin
Almond shaped eyes
Thin upper lip
Narrow nasal bridge
Hypogonadism causes small genitalia in boys

Image from Kidspot

Mucopolysaccharoidosis

Babies with a severe variant of mucopolysaccharoidosis may have coarse facial features from birth, including:

a flat nasal bridge
macroglossia
frontal bossing.
As well as inguinal / umbilical hernias

However, generally the coarse facial features are not present at birth at develop around 12 months of age

Image from Case Report in Italian Journal of Paediatrics

Congenital Hypothyroidism

Jaundice
Widened fontanelle
Macroglossia
Per-orbital oedema
Umbilical hernia

Image from Orphanet Journal of Rare Diseases

Spinal Muscular Atrophy

SMA causes peripheral hypotonia which is evident from the end of the bed by examining the babies posture. SMA causes a typical frog leg position as seen here, compared to a babies posture with normal tone below.

Image from Cure SMA

This is a baby with a normal posture for a term newborn with hips and shoulders abducted and knees and elbows flexed, and fists clenched

Image from Stanford Medical School Website

Congenital Myotonic Dystrophy

Expressionless face
Tented upper lip
Bilateral ptosis
Bilateral wasting of temporalis and masseter muscles as they age
Triangular shaped mouth
Talipes
If you shake the mothers hand you may notice she will have a delayed release of grip

Image from MedLink Neurology

Breathing

In many causes of hypotonia there is also respiratory distress or poor respiratory effort due to muscle weakness.
Hypotonic babies are also at risk of aspirating if they have an unsafe swallow and some causes of hypotonia are associated with an increased risk of lower respiratory tract infection, e.g. mucopolysaccharidosis, T21
Examine for respiratory distress and pattern of breathing.
- In SMA there is paradoxical breathing due to intercostal muscle weakness. In this pattern the chest is drawn in during inspiration and the abdomen is pushed out, and then during exhalation the chest is pushed out and abdomen is sucked in.
- In myotonic dystrophy there is short shallow breaths due to diaphragmatic weakness and these babies can present in respiratory failure shortly after birth
- Increased work of breathing could also be due to sepsis, hypoglycaemia, lower respiratory tract infection or aspiration

Cardiovascular System

Examine for signs of heart failure, and heart murmurs
- Certain inborn errors or metabolism and SMA type 3 are associated with cardiomyopathy, although this usually does not present in infancy.
- Congenital myotonic dystrophy type 2 is associated with arrhythmias, cardiomyopathy and heart failure

Neurological System

Assess tone, posture, deep tendon reflexes and primitive reflexes. Also examine the fontanelle. Check Blood sugar!

Tone is assessed in two ways:

Phasic tone – Deep Tendon Reflexes (the response of the muscle to rapid stretch)
Postural tone – Response of muscle to sustained low-intensity stretch, e.g. head lag on pulling to sit, rag-doll posture when suspended face down horizontally, slipping through the hands when held under the arms.

Image portraying a baby with hypotonia with significant head lag on the left and rag-doll posture on the right

Image from Medicine Today

Image demonstrating the difference between a baby with normal tone being held under the arms (on the left) and a baby with hypotonia being held (on the right) almost slipping through the grip

Image from Annals of Neurology authored by Dr Bryan Burnette, cited from Clinical Gate

Examine deep tendon reflexes, in particular looking for diminished or brisk reflexes.

Examine for primitive reflexes, absence of these suggest a central cause for the hypotonia. Examine:

Moro reflex (a normal moro is symmetrical)
Palmar and plantar grasp
Rooting
Suck
Stepping reflex

Examine the fontanelle to feel if it is bulging (suggesting meningitis) or if it is wide, which can occur with certain metabolic or endocrine conditions.

Everything Else

Examine the abdomen for any organomegaly which can occur in metabolic or storage disorders or SCORTCH infections
Look for signs of jaundice which can occur with hypothyroidism or inborn errors or metabolism. Severe jaundice causing kernicterus may also cause central hypotonia and seizures. Always look at the sclera as in babies with dark skin you may not be able to see that they are jaundiced on general inspection.
Examine the genitalia as some inborn errors of metabolism and Prader Willi cause hypogonadism with small or undescended testes.
Some inborn errors of metabolism can cause an unpleasant or strange odour.
Examine for arythrogryposis or contractures which can happen more with peripheral causes of hypotonia.

Image showing a baby with peripheral hypotonia resulting in arythrogryposis, which may be seen antenatally

Image from article “Distal Arythrogryposis and Lethal Congenital Contracture Syndrome” Desai D et al

Central (Upper Motor Neurone) hypotonia findings:

Normal antigravity movements
Normal or brisk reflexes
Irritability / loud cry
Seizures (these could be focal or generalised tonic clonic)
Dysmorphic features
History suggestive of HIE or birth trauma

Peripheral (Lower Motor Neurone) hypotonia findings:

Reduced or absent antigravity movements
Diminished or absent reflexes
Weak cry
Muscle fasciculations
Myopathic facies (open mouth with tented upper lip / carp mouth, poor seal when sucking, no facial expressions, ptosis)

*During the acute phase of some central causes of hypotonia the infant may appear weak and as if they have a peripheral cause. This is particularly true of HIE, usually within a number of days the signs change to those of central hypotonia.

Investigations

How you investigate depends if you feel there is central or peripheral hypotonia which is why your examination and history are so important for helping narrow down your differentials

Investigations for a Central cause of Hypotonia

Bloods for: FBC, U&Es, LFTs, Bone Profile, Magnesium, Blood gas, Ammonia, Glucose
Cranial USS
Consider a septic screen if there are risk factors for sepsis or the baby is irritable
Consider plasma amino acids and organic acids and urine organic acids if you feel there is an underlying metabolic disorder
Consider a microarray or genetics referral if there are dysmorphisms and a syndrome is suspected
MRI will look for any underlying structural abnormality and will also rule in or out any evidence of HIE
Consider screening for congenital infections
An EEG will inform you as to whether the baby is encephalopathic or if there are any seizures ongoing

Investigations for a Peripheral cause of Hypotonia

Bloods for Creatinine Kinase which can be raised in myopathies
Consider genetic screening to investigate for SMA or myotonic dystrophy
ECHO will be needed early on and then will need to be done regularly to screen for cardiomyopathy
Nerve conduction studies and muscle biopsy may be useful when the baby is older.
Have a low threshold to refer to neurology for their advice

Management

Obviously depends on the cause of hypotonia

Some babies that have severe illness will need respiratroy support and feeding support

An MDT approach is required no matter the cause of hypotonia as the family will need occupational and physiotherapy as well as speech and language, dietician and likely neurology involvement