Which statement best describes the diagnostic test that supports amyotrophic lateral sclerosis?

Which statement best describes the diagnostic test that supports amyotrophic lateral sclerosis?

• A. MRI brain
• B. CSF oligoclonal bands
• C. PET scan
• D. EMG/NCS showing widespread denervation

Answer: (D)

ALS affects motor neurons, so the most informative evidence comes from assessing muscle electrical activity. An EMG with nerve conduction studies reveals widespread denervation and reinnervation across multiple muscle groups, including spontaneous activity at rest (fibrillations and positive sharp waves) and reduced recruitment. This pattern mirrors lower motor neuron loss and, when paired with the clinical signs of upper motor neuron involvement, supports the diagnosis of ALS. Other tests tend to rule out alternatives rather than confirm ALS: MRI of the brain is not specific for ALS, CSF oligoclonal bands point toward demyelinating diseases like MS, and PET scans provide non-specific metabolic information. Therefore, EMG/NCS showing widespread denervation best supports the diagnosis.

ALS affects motor neurons, so the most informative evidence comes from assessing muscle electrical activity. An EMG with nerve conduction studies reveals widespread denervation and reinnervation across multiple muscle groups, including spontaneous activity at rest (fibrillations and positive sharp waves) and reduced recruitment. This pattern mirrors lower motor neuron loss and, when paired with the clinical signs of upper motor neuron involvement, supports the diagnosis of ALS. Other tests tend to rule out alternatives rather than confirm ALS: MRI of the brain is not specific for ALS, CSF oligoclonal bands point toward demyelinating diseases like MS, and PET scans provide non-specific metabolic information. Therefore, EMG/NCS showing widespread denervation best supports the diagnosis.