Magnetic resonance neurography–supported L3–L4 radiculitis presenting as refractory peripatellar neuropathic pain in a patient with diabetes: A case report

RATIONALE: Peripatellar pain is usually attributed to local knee disorders. However, proximal neural lesions can also cause pain around the knee. Third and fourth lumbar (L3-L4) radiculitis presenting mainly as peripatellar neuropathic pain is uncommon and may be missed when typical radicular symptoms are absent. PATIENT CONCERNS: A 75-year-old man with a more than 20-year history of type 2 diabetes presented with severe left peripatellar pain for 10 days. The pain was burning and stabbing and was accompanied by numbness and marked touch-evoked allodynia. The visual analog scale score was 8-9/10, and the Douleur Neuropathique 4 score was 9/10. He had no low back pain, typical radicular pain, motor weakness, or reflex abnormalities. DIAGNOSES: Knee magnetic resonance imaging showed degenerative changes that did not explain the neuropathic pain phenotype. Lumbar magnetic resonance imaging showed no definite compression of the L3 or L4 nerve roots. Electrodiagnostic testing did not provide level-specific localization. Magnetic resonance neurography showed asymmetric hyperintensity involving the left L3 and L4 proximal neural structures, supporting the diagnosis of L3-L4 radiculitis. INTERVENTIONS: Neuropathic pain medications and knee-targeted procedures provided inadequate or only transient relief. The patient was subsequently treated with pregabalin, duloxetine, short-term opioid analgesia, and optimization of glycemic control. OUTCOMES: The pain and allodynia gradually improved within 2 weeks, and analgesic medications were discontinued. At 3 months, the visual analog scale score was 0-3/10 and the Douleur Neuropathique 4 score was 1/10. Touch-evoked allodynia had resolved. LESSONS: L3-L4 radiculitis may present as refractory peripatellar neuropathic pain without low back pain or typical radicular symptoms. When severe neuropathic pain around the knee cannot be explained by local pathology, a proximal neural lesion should be considered. Magnetic resonance neurography may help identify radiculitis that is not evident on conventional lumbar imaging.