Pathology
The pathology of motor neuron degeneration involves the destruction of motor neurons residing in the cortex, brainstem (corticobulbar tracts), cranial motor nuclei and anterior horn cells within the spinal cord, resulting in a range of neurological symptoms.
Aetiology
In roughly 5-10% of cases, this condition is passed down to individuals through genetic inheritance. Mutations in SOD1 and TDP43 genes can cause familial motor neuron degeneration.
Symptoms
- Gait difficulties
- Dysphagia
- Dysarthria
- Weakness
There is no sensory involvement in motor neuron degeneration.
Signs
- Upper motor neuron: spasticity, brisk reflexes, and a positive Babinski
- Lower motor neuron: fasciculations, muscle wasting, and weakness
- Bulbar: dysarthria, dysphagia, tongue fasciculations/atrophy, and brisk jaw jerk
Investigations
- Imaging: MRI brain and spine to exclude other diagnoses.
- Special tests: Nerve conduction studies/electromyography show signs of chronic denervation in muscles.
Treatment
- Medical: Riluzole (anti glutamate antagonist) is the only treatment available.
- Supportive: Non-invasive ventilation, PEG feeding, and communication aids.
Complications
- Infection
- Incontinence
- Spasticity
- Depression
- Dysphagia
Prognosis
The average length of survival for individuals with motor neuron degeneration is usually between 2 and 5 years from onset. There is a five-year survival rate of 25%.
