A 52-year-old woman presented with a 1-year history of weakness and pain of the left lower back radiating to the hip and thigh. She occasionally had pain in the other leg. Past medical history was significant for gallbladder surgery and a C-section.
Examination revealed no demonstrable muscle weakness despite her complaints. The straight leg raising test was positive on the left. Reflexes were 2+, symmetrical except for a decreased (trace) left ankle jerk.
She had decreased sensation in the posterior and outer aspect of the leg. The rest of the neurologic examination was normal.
What is the Differential Diagnosis?
The low back pain, positive straight leg raising test, and absent left ankle reflex indicate an S1 radiculopathy, most likely caused by a ruptured disk. Other causes include masses, infections, or canal stenosis from osteoarthritis. The back pain argues against a diagnosis of sciatic neuropathy.
What Tests should be Done?
An imaging study such as an MRI or CAT scan of the lumbar spine and an EMG should be done.
An EMG Test was Performed
| Nerve and Site | Latency (ms) | Amplitude (mV) | Conduction Velocity (m/s) |
|---|---|---|---|
| Peroneal Nerve R. | Normal ≤ 5.7 | Normal ≥ 3 | Normal ≥ 40 |
| Ankle | 3.7 | 8 | – |
| Fibular head | 9.5 | 7 | 42 |
| Tibial Nerve R. | Normal ≤ 5.3 | Normal ≥ 4 | Normal ≥ 40 |
|---|---|---|---|
| Ankle | 3.2 | 6 | – |
| Pop. fossa | 11.6 | 5 | 45 |
| Nerve | Latency (ms) | Normal Latency ≤ (ms) |
|---|---|---|
| Peroneal nerve R. | 43.1 | 54 |
| Tibial nerve R. | 45.9 | 54 |
| H-reflex R. | 32.6 | 34 |
| H-reflex L. | 34.3 | 34 |
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