Royal Australasian College of Physicians Examinations/Resources/Clinical Exam/Short Cases/Example Cases/Motor Neurone Disease

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Motor Neurone Disease

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Stem: This patient has difficulty speaking. Please examine the relevant cranial nerves and proceed.

Key Signs

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  • XII:
    • Bulbar
      • Tongue weakness
      • wasting
      • fasiculations
    • Psudobulbar
      • Spastic – unable to protrude
  • IX / X
    • Decreased voluntary palate elevation
    • Gag hyperreactive (PB) or absent (B)
  • VII
    • Weakness of facial movement (both)
    • Normal movement with laughing
  • V
    • Weakness of jaw opening / closure (both)
    • Jaw jerk increased (PB) or absent (B)

(B = bulbar / PB = psuedobulbar / PMA = progressive muscular atrophy)

  • Upper / Lower Limbs:
    • Inspection: Wasting / Fasiculations
    • Power: Predominantly distal weakness, esp of finger abduction
    • Reflexes: Usually present in wasted muscles, although may be absent in SMA. Extensor plantar
    • Sensation: Normal
  • Higher centres: Normal function
  • Speech – nasal (bulbar) or indistinct / “Donald Duck” (PB)

Proceed to

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  • ? PEG tube
  • Respiratory weakness
    • Forced Expiratory Time
    • Spirometry / Ask for RFTs

Example Presentation

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This patient has clinical features of motor neurone disease, including mixed bulbar signs such as tongue wasting and fasiculations, with pseudobulbar signs such as increased gag reflex and jaw jerk. In the upper and lower limbs, there are mixed upper and lower motor neurone signs, with extensor plantars, and weakness of the distal muscles, confirming the diagnosis. I would also consider ordering an EMG / nerve conduction studies which I would expect to show denervated muscles with fibrillations, but normal conduction velocities.

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