In evaluating ALS, which test is commonly used to rule out other conditions?

• A. MRI
• B. Spinal tap
• C. EKG
• D. Lumbar puncture

Answer: (B)

When evaluating ALS, doctors try to exclude other conditions that can look like motor neuron disease. A spinal tap (lumbar puncture) is commonly used because it provides cerebrospinal fluid for analysis, helping to identify infections, inflammatory or autoimmune processes, or other disorders of the nervous system that could explain the weakness.CSF testing can reveal infectious agents, inflammatory markers, or patterns such as oligoclonal bands that suggest diseases like multiple sclerosis, or other findings that point away from ALS. If CSF results are not indicative of an alternative disease and imaging doesn’t reveal a different cause, the likelihood of ALS increases in the overall evaluation. MRI is helpful to exclude structural problems, but the spinal tap specifically targets conditions that could masquerade as ALS at a cellular level. An EKG, by contrast, doesn’t address the neural causes of weakness and is not used to rule in or out ALS.