motor neuron disease

Question 1

definition

Answer 1

A progressive neurodegenerative disorder of cortical, brainstem and spinal motor neurons (lower and upper motor neuron).

Various subtypes:

• Amyotrophic lateral sclerosis (ALS) or Lou Gehrig’s disease: combined degeneration of upper and lower motor neurones producing a mix of UMN and LMN neurones.
• Progressive muscular atrophy variant: Only LMN signs, e.g. flail arm or flail foot syndrome. Better prognosis.
• Progressive bulbar palsy variant:1 Dysarthria and dysphagia with wasted fasciculating tongue (LMN) and brisk jaw jerk (UMN).
• Primary lateral sclerosis variant: UMN pattern of weakness, brisk reflexes, extensor plantar responses, without LMN signs.

Question 2

symptoms

Answer 2

• Weakness of limbs (focal or asymmetrical).
• Speech disturbance (slurring or reduction in volume).
• Swallowing disturbance (e.g. choking on food, nasal regurgitation).
• There may be behavioural changes (e.g. disinhibition, emotional lability).

Question 3

examination

Answer 3

Combination of upper motor neuron (UMN) and lower motor neuron (LMN) signs often affecting several regions asymmetrically.

LMN features: Muscle wasting, fasciculations, flaccid weakness, depressed or absent reflexes.
UMN features: Spastic weakness, brisk reflexes, extensor plantars.

Sensory examination: Should be normal!!!!

Question 4

investigations

Answer 4

clinical diagnosis!

Investigations aimed to confirm the diagnosis by providing evidence of combined UMN and LMN loss and excluding other causes.
- Blood: CK (slightly raised), ESR.
Consider testing for anti-GM1 ganglioside antibodies (present in multifocal motor neuropathy2).
- Electromyography (EMG): Features of acute and chronic denervation with giant motor unit action potentials in more than 1 limb and/or paraspinals.
- Nerve conduction studies: Most often normal.
- MRI: To exclude cord or root compression, and brainstem lesion in progressive bulbar palsy variant. May show high signal in motor tracts on T2 imaging.