1517 - Beyond the Bulge: When Disc Disease Doesn’t Explain the Deficit

A 53-year-old man developed sudden left buttock pain while at rest, which radiated down his leg the next day.  Over several days, he noted progressive dorsiflexion weakness, burning pain, and numbness in the left lateral leg.  Lumbar spine MRI without contrast showed only mild degenerative changes with a small L5-S1 disc bulge. He was diagnosed with L5 radiculopathy and underwent lumbar epidural steroid injections without improvement. Electrodiagnostic studies revealed denervation in the left L5 myotome with absent sensory responses, consistent with a lumbosacral plexopathy. Patient was referred to neuromuscular clinic where MRI neurography with/without contrast of the pelvis showed edema and thickening of the L5-S1 nerve roots and sciatic nerve without focal compression. Based on presentation, imaging, and electrodiagnostic findings, he was diagnosed with non-diabetic LRPN. The patient received high-dose steroids. He completed physical therapy, was fit with an orthosis, but continued to have significant dorsiflexion weakness.

Discussions: LRPN is thought to result from an immune-mediated microvasculitis of the vasa nervorum, producing ischemic injury of the plexus and nerve roots. Clinically, it can mimic radiculopathy, leading to potentially avoidable spinal procedures. Accurate diagnosis requires a high index of suspicion, as LRPN remains largely a diagnosis of exclusion. Although many patients improve, recovery is often delayed and incomplete.

Conclusions: This case underscores the importance of considering LRPN in patients with acute or subacute monophasic, asymmetric pain and weakness. Though more common in diabetes, it also occurs in non-diabetics. Comprehensive evaluation, particularly with electrodiagnostic testing, can prevent misdiagnosis and guide more appropriate management.