1324 - When Radiculopathy Isn’t Just Radiculopathy: Malignant Peripheral Nerve Sheath Tumor Mimicking Lumbar Radiculopathy in a Patient with Rectal Cancer

A 56-year-old male with past medical history of metastatic rectal cancer on surveillance presented to an outpatient oncology rehab clinic with new onset lower back pain with radiation of the pain into the left lower extremity.  Initial MRI showed L5-S1 anterolisthesis with S1 spondylolisthesis and moderate L5-S2 neuroforaminal stenosis. Electromyography was consistent with left-sided lumbosacral radiculopathy at S1. The patient underwent L5-S1 and repeat L5-S1 and S1-2 TFESI with no improvement of symptoms. Patient continued to have worsening pain, not responsive to pain medications, neuropathic medications, and physical therapy. Repeat imaging several months later revealed new soft tissue nodularity along the piriformis muscle with involvement of the sciatic nerve. Biopsy confirmed a malignant peripheral nerve sheath tumor consistent with recurrence of rectal cancer. The patient is now undergoing palliative radiation therapy for pain control.

Discussions: This case highlights the diagnostic challenge of distinguishing radiculopathy due to degenerative spine disease from symptoms secondary to malignancy. While the patient’s presentation was initially consistent with classic radiculopathy, progression of pain despite appropriate conservative measures prompted further investigation. Repeat imaging identified a malignant peripheral nerve sheath tumor involving the sciatic nerve, representing an unusual cause of radicular symptoms in the setting of metastatic rectal cancer.

Conclusions: Patients with a history of cancer should be monitored closely for new or progressing pain symptoms, even when they mimic common conditions such as lumbar radiculopathy. New onset or worsening of existing symptoms may present as the first signs of progression of disease or disease recurrence. This case underscores the importance of maintaining a broad differential diagnosis in oncology patients and considering malignant etiologies when symptoms fail to respond to conventional treatment.