IV. Diseases with spinal cord and/or cerebellum involvement
A. Amyotrophic lateral sclerosis (ALS): one type of motor neuron disease
1. Age of Onset: middle‑aged and elderly (usually older than 50 years)
2. Location of Lesions: degeneration of both upper and lower motor neurons, i.e., cortical pyramidal cells, neurons in cranial nerve nuclei, anterior horn cells are all involved. Degeneration of the corticospinal tract axons and peripheral nerves occurs in association with the neuronal degeneration.
3. Pathogenesis: unknown; approximately 10% of cases appear to be familial, with an autosomal dominant inheritance pattern.
4. Clinical Presentation: symptoms expected of upper motor neuron dysfunction (hyperactive reflexes, Babinski signs) and/or lower motor neuron dysfunction of either cranial nerves or spinal nerves (weakness, dysphagia, dysphonia, muscular wasting and fasciculations, pulmonary insufficiency).
5. Gross Pathology: atrophy of anterior horns and ventral nerve roots; cortical atrophy.
6. Microscopic Pathology: loss of anterior horn cells in spinal cord and motor neurons in the motor strip; Wallerian degeneration.
7. Effect on Muscle: causes denervation atrophy of affected muscles.