Delayed-onset lumbosacral polyradiculitis following proton precision beam therapy for localized prostate cancer: A case report.

Introduction: In males, prostate cancer is the second most diagnosed cancer worldwide and the sixth leading cause of cancer death. Radiation therapy is a common treatment modality for prostate cancer but carries a multitude of adverse effects, ranging from radiation cystitis to post-radiation neuropathy. Proton beam therapy has gained attention as a valuable alternative, due to its improved precision with targeted dose delivery and reduced toxicity. However, the risk for radiation-induced complications, such as radiation-induced lumbar radiculopathy, is not fully understood and requires further investigation. Case presentation: We present a 68-year-old man with delayed-onset lumbosacral polyradiculitis following proton precision beam therapy for localized prostate cancer. The patient underwent proton therapy treatment for the prostate and seminal vesicles with favorable results and tumor remission. However, five months after completing radiation therapy, the patient presented with chronic lower extremity pain, weakness, and bilateral lower extremity paresthesias. MRI showed diffuse hyperintensity of bilateral L5-S3 nerve roots and an intramuscular edema-like signal involving the bilateral obturator externus and internus muscles, likely due to radiation. Additionally, EMG findings suggested the presence of chronic bilateral L5 radiculopathy. Conclusion: The clinical manifestation of delayed-onset radiation-induced lumbosacral plexopathy is a rare and uncommon complication of external beam radiation therapy that presents as radicular or myelopathic symptoms based on the location and severity of the inflammation. This case highlights the need for continued follow-up post-radiation and emphasizes the need for a comprehensive review of the oncological history of cancer patients.