Motor Neuron Disease

Motor Neuron Disease (MND)

DR FAROOQ SATTAR DHEDHI

• Motor neuron disease (MND) is a progressive neurodegenerative disorder.
• Characterised by selective loss of motor neurons in brain and spinal cord.
• Leads to muscle weakness, wasting, and fasciculations.
• Most common form: Amyotrophic Lateral Sclerosis (ALS).

Motor neuron disease

• Motor neuron disease is degenerative disease which selectively affect motor tract fibers
• (corticospinal tract+ anterior horn cell)
  • ↓
  • ↓
• UMN signs                                      LMN signs

Motor pathway

A flowchart illustrating the motor pathway from the cortex motor area to muscle, and the feedback loops involving motor neuron disease.

Epidemiology

• Incidence: ~2 per 100,000 per year.
• Peak onset: 50–70 years.
• More common in males (ratio 1.5:1).
• 5–10% familial, rest sporadic.
• Degeneration of upper and lower motor neurons.
• Upper motor neuron (UMN): corticospinal tract degeneration.
• Lower motor neuron (LMN): anterior horn cell and cranial motor nuclei loss.
• Excitotoxicity (glutamate), oxidative stress, genetic mutations implicated.
• Sporadic:90% unclear
• Inherited:10% familial ALS,25% mutation in gene encoding copper zinc super oxide dismutase (SOD1)
• Is progressive : median survival is approximately 3y

Clinical Features – UMN Signs

• Spasticity.
• Hyperreflexia.
• Extensor plantar response (Babinski sign).
• Stiffness and clumsy movements.

Clinical Features – LMN Signs

• Muscle weakness (asymmetrical, distal > proximal).
• Muscle wasting.
• Fasciculations.
• Cramps.

Clinical Features – Bulbar Involvement

• Dysarthria (slurred speech).
• Dysphagia (difficulty swallowing).
• Tongue wasting and fasciculations.
• Spastic tongue
• Emotional lability (pseudobulbar affect).

A Amyotrophic lateral sclerosis

B C8 radiculopathy

• Classic ALS (amyotrophic lateral sclerosis)..UMN+LMN signs

• others

  • Progressive muscular atrophy
  • Primary lateral sclerosis
  • Progressive bulbar palsy
  • Progressive pseudo bulbar palsy

• Mixed lower motor neuron + upper motor neuron signs

• Early patient may exhibit only LMN signs or upper LMN signs

• Weakness begin a symmetrical and distally then spread to involve contiguous group of motor neurons

• Bulbar & pesudobulber palsy involvement ..dysphagea & dysarthria

• Nooooooooooooo

• Cognitive

• Sensory

• Ocular muscles

• Autonomic Sphincter dysfunction

Diagnosis

• El Escorial criteria for dx

• Definitive

• Probable

• possible

• Electromyography (EMG): denervation and fasciculations.

• Nerve conduction studies (NCV): normal sensory, reduced motor.

• MRI brain/spinal cord: to exclude other causes.

• Genetic testing in familial cases.

• NCS: sensory..N
  motor:normal or decreased amplitude

• EMG: denervation

• MRI normal

• No specific diagnostic test – clinical diagnosis.

Differential Diagnosis

• Multifocal motor neuropathy.
• Cervical myelopathy.
• Multiple sclerosis.
• Myasthenia gravis.
• Inclusion body myositis.

Split hand sign: Amyotrophic lateral sclerosis (1st clinical sign)

Atrophy of

1. 1st Dorsal interossei
2. Abductor pollicis brevis

(wasting of thenar eminence, but sparing of hypothenar eminence)

Differentiated from C8 radiculopathy by

1. Sensory involvement
2. Hypothenar wasting

A Amyotrophic lateral sclerosis

B C8 radiculopathy

• No cure, treatment is supportive and symptomatic.
• Riluzole: prolongs survival by few months (ALS).
• Edaravone: slows progression (in some cases).
• Non-invasive ventilation for respiratory failure.
• Multidisciplinary care: physiotherapy, speech therapy, nutrition support.

Prognosis

• Progressive and ultimately fatal disease.
• Median survival: 3–5 years from symptom onset.
• Respiratory failure is the commonest cause of death.
• Better prognosis in younger onset and slowly progressive variants.

Summary

• MND is a progressive neurodegenerative disorder of motor neurons.
• ALS is the most common type with both UMN and LMN features.
• Clinical diagnosis supported by EMG, MRI to exclude mimics.
• No cure – Riluzole and supportive care improve survival and quality of life for only few months.
• Prognosis poor, with respiratory failure leading to death.