Which disease primarily involves degeneration of motor nerve cells in the brain and spinal cord?

Which disease primarily involves degeneration of motor nerve cells in the brain and spinal cord?

• A. Amyotrophic lateral sclerosis
• B. Alzheimer's disease
• C. Multiple sclerosis
• D. Parkinson's disease

Answer: (A)

This item tests recognition of a motor neuron disease that affects both the brain and spinal cord, leading to progressive muscle weakness and atrophy. The disease that fits this description is ALS, because it involves degeneration of motor neurons throughout the CNS, including both upper motor neurons in the brain and lower motor neurons in the spinal cord and brainstem. This double hit produces a combination of signs: spasticity and hyperreflexia from upper motor neuron loss, along with muscle wasting and fasciculations from lower motor neuron loss, ultimately advancing to breathing difficulties as the muscles of respiration weaken. Other conditions don’t fit this pattern: Alzheimer's disease primarily involves cortical neurons and affects memory and cognition rather than the motor pathways; multiple sclerosis is a demyelinating disease with a wide range of neurologic symptoms depending on where lesions occur, not a primary degeneration of motor neurons; Parkinson's disease results from loss of dopaminergic neurons in the substantia nigra, leading to tremor, rigidity, and bradykinesia, not a direct motor neuron degeneration.

This item tests recognition of a motor neuron disease that affects both the brain and spinal cord, leading to progressive muscle weakness and atrophy. The disease that fits this description is ALS, because it involves degeneration of motor neurons throughout the CNS, including both upper motor neurons in the brain and lower motor neurons in the spinal cord and brainstem. This double hit produces a combination of signs: spasticity and hyperreflexia from upper motor neuron loss, along with muscle wasting and fasciculations from lower motor neuron loss, ultimately advancing to breathing difficulties as the muscles of respiration weaken.

Other conditions don’t fit this pattern: Alzheimer's disease primarily involves cortical neurons and affects memory and cognition rather than the motor pathways; multiple sclerosis is a demyelinating disease with a wide range of neurologic symptoms depending on where lesions occur, not a primary degeneration of motor neurons; Parkinson's disease results from loss of dopaminergic neurons in the substantia nigra, leading to tremor, rigidity, and bradykinesia, not a direct motor neuron degeneration.