Lumbosacral plexopathy can result when radiation, used in the treatment of various neoplasms, is directed toward management of abdominal and pelvic malignancies.
Anatomically, the lumbosacral plexus consists of lumbar (L1-L4) and sacral (L5-S5) portions, which are connected by the lumbosacral trunk (L4-L5). The L1-L4 nerve roots transverse through the psoas muscle and then coalesce into the lumbar plexus, which then divides into anterior and posterior divisions. The first 3 nerves (iliohypogastric, ilioinguinal, and femoral) of the 7 major branches of lumbar plexus provide motor and sensory innervation to the abdominal wall. The next 3 nerves (lateral femoral cutaneous, femoral, and obturator) innervate the anteromedial thigh. The femoral nerve terminates in the saphenous nerve providing sensation along the medial aspect of the leg.
The sacral plexus also divides into anterior and posterior divisions, which further divide into various peripheral nerves, providing sensory motor innervation to posterior hip girdle, thigh, and anterior and posterior leg. The 5 main nerves are the superior gluteal, inferior gluteal, posterior femoral cutaneous, sciatic, and pudendal. The sciatic nerve divides into the common peroneal and tibial nerves in the thigh.
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The effects of radiation are correlated with the dose, technique, and concomitant use of chemotherapy. Risk particularly increases with intracavitary radiation.  The mechanism may be related to a combination of localized ischemia and subsequent soft-tissue fibrosis due to microvascular insufficiency. With doses above 1000 cGy, pathologic changes can be seen in Schwann cells, endoneurial fibroblasts, vascular cells, and perineural cells. Injury to anterior and posterior nerve roots in rodents has been shown with doses of 3500 Gy. However, combined modality therapy may alter predicted tolerability and potential for late effects.
Radiation-induced lumbosacral plexopathy is rare (0.3-1.3% of patients treated with radiation). It was noted in 1.3% of patients after abdominal irradiation and in 0.32% of patients after pelvic irradiation.
The international incidence of radiation-induced lumbosacral plexopathy is unknown.
Generally, the symptoms of radiation-induced lumbosacral plexopathy progress gradually and with variable rapidity. Clinical manifestations of the condition have appeared 3 months to 22 years after the completion of radiation therapy.  Jaeckle and colleagues found that 20% of patients developed moderate or even severe weakness over 6 months.  Others were found to have mild weakness at 4-5 years following the onset of neurologic symptoms.
No race predilection for radiation-induced lumbosacral plexopathy has been reported.
The male-to-female ratio is 1:1.2.
Age at the time of presentation ranges from 34-68 years, with a median age of 47.5 years.
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