🧠 MOCK OSCE · FCPS, MCPS, MD PAEDIATRICS ⏱ 10 min · NEUROMUSCULAR · FLOPPY INFANT

Floppy Infant · Short Case

Candidate task: perform focused neuromuscular examination on a child with suspected neuromuscular disorder (floppy infant).
Then discuss differential diagnosis, investigations, management & follow‑up.
Pre‑exam Protocol
⏤ · Wash, Warm, Introduce, Position, Expose, Approach ▾

Standard pre‑examination protocol – must be demonstrated:

🖐 Wash hands with sterilizing solution.
🔥 Warm hands and stethoscope.
👋 Introduce yourself to child & parent.
🧍 Position child: supine, then sitting (if possible).
👕 Exposure — fully expose for neuromuscular exam, warm environment.
➡️ Approach from the right side.
✔ CPSP marker: Pre‑exam Protocol is observed and scored.
1. Clinical Examination (≈6 min)
02 General Look (Inspection from end of bed) ▾

Key observations – “Floppy infant” clues:

  • Posture: frog‑leg position (hips abducted, externally rotated) – suggests hypotonia.
  • Movement: paucity of spontaneous movement (Werdnig‑Hoffmann), or “flail” limbs.
  • Facial features: myopathic face (ptosis, open mouth, tented upper lip) – myotonic dystrophy, congenital myopathies.
  • Respiratory: paradoxical breathing, bell‑shaped chest (intercostal weakness) – SMA type 1.
  • Skin: neurocutaneous stigmata, joint contractures (arthrogryposis).
  • Behaviour: alert, bright eyes (SMA type 1) vs lethargy (central cause).
👁 Red flags: tongue fasciculations + areflexia + frog‑leg posture → SMA type 1.
03 Neuromuscular Examination (Tone, Power, Reflexes, Primitive Reflexes) ▾

Systematic neuromuscular exam – “180° examination” sequence:

  • Supine: observe posture, spontaneous movements, frog‑leg position.
  • Traction response (pull to sit): head lag (weakness) vs normal head control.
  • Sitting: head control, truncal support (normally achieved by 6‑8 months).
  • Weight bearing (vertical suspension): scissoring (CP), or slipping through (hypotonia).
  • Ventral suspension: “C” shape (severe hypotonia) vs normal (head above trunk).
  • Prone: ability to lift head/chest.
  • Tone: passive range of motion, scarf sign, traction response.
  • Power: antigravity movements, withdrawal response.
  • Reflexes: deep tendon reflexes – absent in SMA, brisk in central hypotonia.
  • Primitive reflexes: Moro (absent in SMA), grasp, stepping, ATNR.
🔍 Key: absent reflexes + tongue fasciculations + hypotonia → anterior horn cell disease (SMA).
04 General Physical Exam (Hands → Face → Chest → Abdomen → Limbs) ▾

Systematic examination:

  • Hands: small, fine (Prader‑Willi); contractures; thenar wasting.
  • Face: myopathic facies (myotonic dystrophy, congenital myopathies); tongue fasciculations (SMA).
  • Chest: bell‑shaped, intercostal recession (SMA); auscultate for aspiration (bulbar weakness).
  • Abdomen: hepatomegaly (storage disorders – Pompe, GSD); umbilical hernia (Prader‑Willi).
  • Limbs: joint contractures (arthrogryposis, congenital muscular dystrophy); muscle wasting.
  • Back: scoliosis, midline defects (spina bifida).
📏 Anthropometry: weight, length, head circumference – plot growth.
05 Developmental Assessment & Associated Signs ▾

Assess:

  • Motor milestones: delayed or regression (SMA, metabolic).
  • Social: bright, alert (SMA type 1) vs delayed (central hypotonia).
  • Speech/feeding: poor suck, dysphagia (bulbar weakness).
  • Syndromic: dysmorphic features (Prader‑Willi, Down, myotonic dystrophy).
  • Eyes: ptosis, ophthalmoplegia (myasthenia, congenital myopathies).
🧠 Genetic clues: floppy + dysmorphic + hypogonadism → Prader‑Willi (15q11‑13).

📋 Case Presentation – (fill in during exam)

This is a _____-month-old _____ child, referred for _____ (hypotonia / weakness / feeding difficulties). On examination, the child appears _____ (alert / lethargic), with _____ (frog‑leg posture / normal). Cranial nerves: _____ (tongue fasciculations / ptosis / normal). Tone: _____ (profoundly hypotonic / normal). Power: _____ (poor antigravity / preserved). Reflexes: _____ (absent / brisk / normal). Primitive reflexes: _____ (Moro absent / present). Respiratory: _____ (paradoxical breathing / normal). Growth: weight _____ percentile, length _____ percentile, head circumference _____ percentile. Associated signs: _____ (contractures / dysmorphism / hepatomegaly).

2. Viva Discussion (≈4 min)
06 Viva · Differential, Investigations, Management, Follow‑up ▾
🔹 Differential Diagnosis

• Spinal muscular atrophy (SMA) type 1 – areflexia, tongue fasciculations, frog‑leg posture
• Congenital myopathies (nemaline, central core) – weakness, normal CK
• Congenital muscular dystrophy – elevated CK, contractures
• Congenital myotonic dystrophy – maternal history, myopathic facies
• Infantile botulism – descending paralysis, constipation, ptosis
• Metabolic myopathies – Pompe (cardiomegaly), GSD, mitochondrial
• Central hypotonia – CP, Down, Prader‑Willi (normal reflexes, dysmorphic)
• Neuromuscular junction – transient neonatal myasthenia, congenital myasthenic syndrome
• Peripheral neuropathy – Charcot‑Marie‑Tooth, congenital hypomyelinating

🔹 Investigations – Diagnosis

• Genetic testing: SMA (SMN1 deletion) – first line.
• Creatine kinase (CK): normal in SMA, elevated in dystrophies.
• Electromyography (EMG): neurogenic (SMA) vs myopathic (myopathies).
• Nerve conduction studies: normal in SMA, slow in neuropathies.
• Muscle biopsy: for congenital myopathies, metabolic disorders.
• Brain MRI: if central cause suspected.

🔹 Investigations – Aetiology

• SMA gene testing: SMN1 homozygous deletion (95%).
• Metabolic screen: lactate, ammonia, amino acids, acylcarnitine.
• TORCH: if congenital infection suspected.
• Chromosomes: Prader‑Willi (FISH for 15q11‑13).
• Maternal history: myotonic dystrophy, myasthenia gravis.

🔹 Investigations – Exclude Others

• Brain MRI: to exclude structural/central causes.
• Lumbar puncture: if infection (botulism, meningitis).
• Echocardiogram: if Pompe or mitochondrial suspected.
• EMG/NCS: to differentiate myopathy vs neuropathy vs NMJ.

🔹 Investigations – Rule Out Complications

• Pulmonary function: FVC, sleep study (SMA, myopathies).
• Swallow study: aspiration risk (bulbar weakness).
• ECG/ECHO: cardiomyopathy (myotonic dystrophy, mitochondrial).
• Orthopedic: X‑ray for scoliosis, hip dislocation.
• Genetic counselling: recurrence risk, prenatal diagnosis.

🔹 Management – Across Organ Systems

Respiratory

Non‑invasive ventilation (BiPAP), cough assist, chest physiotherapy. Avoid respiratory infections.

Nutrition

High‑calorie feeds, NG tube or gastrostomy for dysphagia. Monitor for aspiration.

Orthopedic

Physiotherapy, stretching, splints; manage scoliosis, hip dislocation.

Genetic/Medication

SMA: nusinersen, risdiplam, gene therapy. Myotonic: mexiletine for myotonia. Myasthenia: pyridostigmine.

Palliative

Discuss prognosis, advanced care planning, support for family.

Multidisciplinary

Neurology, respiratory, genetics, physiotherapy, occupational therapy, dietitian, social work.

📈 Prognosis

  • SMA type 1 (untreated): death by 2 years (respiratory failure).
  • SMA type 1 (treated): improved survival, motor milestones with nusinersen/risdiplam.
  • Congenital myopathies: usually non‑progressive; variable severity.
  • Congenital myotonic dystrophy: severe; early mortality, but survivors improve.
  • Infantile botulism: excellent recovery with supportive care and antitoxin.
  • Central hypotonia: depends on underlying cause (CP, syndrome).

📋 Follow‑up Schedule

  • SMA: monthly/3‑monthly during therapy titration; then 3‑6 monthly.
  • Congenital myopathy: annually for respiratory, orthopedics.
  • Botulism: weekly until recovery; then discharge.
  • Central hypotonia: routine developmental surveillance.
💡 Examiner expectation: logical differential (central vs peripheral), systematic investigation (genetic first for SMA), and a management plan covering respiratory support, nutrition, and emerging therapies. Know the SMN1 deletion test as first‑line for suspected SMA.
📚 Visit paeds.online for more CPSP resources
Mock OSCE · Floppy Infant · Based on Wyne‑Harris, Nelson & Pediatric Clinical Advisor