A 52-year-old man with a 6-month history of lower back pain radiating to the left leg presents to the pain clinic. Clinical examination suggests nerve root compression. Before initiating interventional pain management, which investigation is most appropriate to confirm the diagnosis and localize the exact level of pathology?

## Investigation of Choice for Radiculopathy Localization ### Clinical Context The patient presents with classic radiculopathy: lower back pain with dermatomal radiation, suggesting nerve root compression. Confirmation and precise anatomical localization are essential before any interventional procedure. ### Why MRI is the Gold Standard **Key Point:** MRI of the lumbar spine is the investigation of choice for suspected nerve root compression because it provides: - Superior soft tissue contrast (disc, ligament, nerve root visualization) - Direct visualization of neural structures without radiation - Multiplanar imaging capability (axial, sagittal, coronal) - Ability to identify disc herniation, stenosis, and foraminal compromise **High-Yield:** MRI has >90% sensitivity and specificity for detecting disc herniation and nerve root compression at the level causing symptoms. ### Comparison with Other Modalities | Investigation | Sensitivity for Disc Herniation | Radiation | Soft Tissue Detail | Best Use | |---|---|---|---|---| | Plain X-ray | ~30% | Yes | Poor | Screening only, bony anatomy | | MRI | >90% | No | Excellent | Gold standard for nerve compression | | CT | ~70% | Yes | Moderate | Bony stenosis, post-fusion assessment | | EMG/NCS | N/A | No | Functional assessment | Confirms denervation, not anatomical | **Clinical Pearl:** While EMG/NCS can confirm denervation, it does NOT localize the anatomical lesion or show the structural cause — it is a functional test, not a diagnostic imaging modality. ### Timing and Indications **Key Point:** MRI should be obtained BEFORE interventional procedures (epidural injection, nerve blocks) to: 1. Confirm the diagnosis 2. Identify the exact spinal level 3. Rule out contraindications (e.g., cauda equina syndrome, infection) 4. Plan the approach for intervention **Warning:** Plain radiography alone is insufficient for soft tissue pathology and will miss ~70% of clinically significant disc herniations.