Neurological examination across childhood — formative SAQs

SAQ 1 (10 marks)

A four-month-old infant, born at 30 weeks gestation and now assessed at corrected age, is seen in the neonatal follow-up clinic. The mother reports that the baby is feeding slowly and seems stiff down the right side. On examination, the head circumference is on the 50th centile and tracking along it, the anterior fontanelle is soft and flat, and the baby is alert and socially engaged. The tone is increased in the right arm and leg with a velocity-dependent catch on fast stretch, the right hand is fisted, the deep tendon reflexes are brisk on the right with a few beats of unsustained clonus at the right ankle, and the plantar response is extensor on the right. The General Movements Assessment shows absent fidgety movements. [4] [8]

a) Explain why an extensor plantar response and a few beats of ankle clonus are interpreted differently in a four-month-old infant than they would be in a four-year-old child. (3 marks) [2]

b) Describe how you would assess tone in this infant, naming the bedside manoeuvres, and classify the abnormal tone using the Task Force on Childhood Motor Disorders definitions. (3 marks) [6]

c) State the significance of the absent fidgety movements, name the window in which the General Movements Assessment is most informative, and outline the integrated early-detection pathway for suspected cerebral palsy. (3 marks) [4] [8]

d) Give your disposition, naming the neuroimaging modality of choice and the safety-net you would give the family. (1 mark) [9]

SAQ 2 (10 marks)

A three-month-old term infant is referred by the general practitioner as a floppy baby who does not move much and has a weak cry. On examination the infant lies in a frog-leg posture, is alert and socially engaging with good eye contact and a social smile, but moves all four limbs very little and only the distal movements are visible. The tone is globally and symmetrically reduced, the deep tendon reflexes are absent at the knees and ankles, and tongue fasciculations are present. The mother reports the movements have been progressively reduced over the last six weeks. [10] [12]

a) Using the reflex pattern and the social engagement, classify the hypotonia as central or peripheral and justify your call. (3 marks) [10]

b) Give the most likely diagnosis, name two further focused investigations, and explain why the history of progressive reduction in movement changes the urgency. (3 marks) [11]

c) Contrast this infant with a floppy infant in whom the tone is reduced but the reflexes are preserved and brisk, the primitive reflexes persist, and social engagement is reduced. Name the likely class of cause and two examples. (2 marks) [10]

d) Explain why distinguishing developmental delay from developmental regression is critical, and describe how you would establish the trajectory from the history. (2 marks) [12]

Marking guide

SAQ 1. An extensor (upgoing) plantar response and a few beats of unsustained ankle clonus are normal in young infants because the corticospinal tracts are incompletely myelinated at birth, and the inhibitory pathway that flexes the toe matures over the first twelve to twenty-four months. In a four-month-old these are read against the rest of the examination and accepted if isolated; in a four-year-old an upgoing plantar is an upper motor neuron sign, and sustained clonus is always abnormal. Here the finding is asymmetric — extensor on the right only — and paired with right-sided hypertonia and brisk reflexes, so it is pathological in context. [2]

Tone is assessed by passive movement of each joint through its full range, slowly and then quickly to feel for the velocity-dependent catch, plus the traction response (pull to sit and watch the head and limbs), ventral suspension (held prone, the infant should flex the limbs and hold the head near horizontal), and vertical and horizontal suspension. The abnormal tone here is spasticity — a velocity-dependent increase in resistance on fast stretch — as defined by the Task Force on Childhood Motor Disorders, distinguishing it from dystonia (co-contraction with movement) and rigidity (continuous, velocity-independent resistance). [6]

Absent fidgety movements at the fidgety age are among the strongest single predictors of cerebral palsy. The General Movements Assessment is most informative at corrected age nine to twenty weeks post-term, when the normal repertoire shows continuous, variable, low-amplitude movements of the neck, trunk and limbs. The integrated early-detection pathway combines the General Movements Assessment, the Hammersmith Infant Neurological Examination, and magnetic resonance imaging to make an early, accurate diagnosis of cerebral palsy, ideally before corrected age six months, with early intervention begun in the window of greatest neuroplasticity. [4] [8]

The disposition is referral to paediatric neurology and developmental services, with magnetic resonance imaging of the brain as the modality of choice to define the lesion (here likely a periventricular leukomalacia with a right-sided predominance). The safety-net is to return urgently with any change in feeding, breathing, conscious state, seizures, or a rapid change in tone or head size. [9]

SAQ 2. The hypotonia is peripheral — the reflexes are absent in proportion to the weakness, yet the infant is alert and socially engaged with a preserved social smile, which excludes a primary central (brain) cause. A central cause would preserve or increase the reflexes and typically reduce the social engagement or add seizures and dysmorphism. [10]

The most likely diagnosis is spinal muscular atrophy, supported by the severe symmetric proximal weakness, the areflexia, and the tongue fasciculations in an alert infant. The focused investigations are genetic testing for the survival motor neuron gene (the diagnostic test) and electromyography and nerve conduction studies to confirm the anterior horn cell localisation if the genetic result is pending. The progressive reduction in movement over six weeks signals a progressive lower motor unit disorder, which raises the urgency because spinal muscular atrophy can compromise the respiratory muscles over weeks to months and because disease-modifying therapy is now available and time-critical. [11]

A floppy infant with reduced tone but preserved or brisk reflexes, persistent primitive reflexes, and reduced social engagement has a central cause of hypotonia — the brain is the seat of the problem. Two examples are a hypoxic-ischaemic encephalopathy with residual injury and a chromosomal syndrome such as Down syndrome; a benign congenital hypotonia is a diagnosis of exclusion in this group. [10]

Delay is the slow acquisition of skills that are still being gained; regression is the loss of skills once held. The distinction is critical because delay warrants surveillance and routine referral, whereas regression is an emergency demanding urgent investigation for a neurodegenerative, metabolic, structural or severe epileptic process. The trajectory is established by asking explicitly, at three and six months ago, whether each skill — movement, vocalisation, social smile — was the same, better, or worse, and by documenting the trend over serial visits, because the family will rarely volunteer regression spontaneously. [12]