Motor neuron disease is a neurological condition of unknown cause which can present with both upper and lower motor neuron signs. It rarely presents before 40 years and various patterns of disease are recognised including:

• Amyotrophic lateral sclerosis (most common) - UMN and LMN disease
• Progressive bulbar palsy(second most common) - Affecting muscles of talking and swallowing
• progressive muscular atrophy (10%) - exclusively LMN signs
• Primary lateral sclerosis - progressive and bilateral UMN signs

Pathophysiology

There is a progressive degeneration of both upper and lower motor neurones. The sensory neurones are spared.

Exact cause is unknown

Risk factors:

• Positive family Hx (genetic component, 5-10% of cases are inherited)
• smoking
• exposure to heavy metals
• certain pesticides.

PC

• A mixture of upper and lower motor neurone signs + Absence of sensory signs/symptoms

Signs of lower motor neurone disease:

• Muscle wasting
• Reduced tone