eMedicine Specialties > Physical Medicine and Rehabilitation > Plexopathy

Radiation-Induced Lumbosacral Plexopathy

Author: Rajesh R Yadav, MD, Assistant Professor, Section of Physical Medicine and Rehabilitation, MD Anderson Cancer Center, University of Texas at Houston
Contributor Information and Disclosures

Updated: Oct 17, 2008

Introduction

Background

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.

Related eMedicine topics:
Radiation-Induced Brachial Plexopathy

Pathophysiology

The effects of radiation are correlated with the dose, technique, and concomitant use of chemotherapy. Risk particularly increases with intracavitary radiation.¹ 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 particularly noted with uterine, cervical, ovarian, and testicular cancers, as well as with lymphomas.

Frequency

United States

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.

International

The international incidence of radiation-induced lumbosacral plexopathy is unknown.

Mortality/Morbidity

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.² Jaeckle and colleagues found that 20% of patients developed moderate or even severe weakness over 6 months.³ Others were found to have mild weakness at 4-5 years following the onset of neurologic symptoms.

Race

No race predilection for radiation-induced lumbosacral plexopathy has been reported.

Sex

The male-to-female ratio is 1:1.2.

Age

Age at the time of presentation ranges from 34-68 years, with a median age of 47.5 years.

Clinical

History

With prior radiation treatment and initial symptoms, a recurrent tumor may need to be distinguished from postradiation plexopathy. The median symptom-free interval for radiation-induced lumbosacral plexopathy, from treatment to the initial neurologic symptom, is 5 years, with a range of 1-31 years.²

• Patients with radiation-induced lumbosacral plexopathy most commonly present with painless weakness in 1 or both legs. Pain is present initially in only 10% of patients, although ultimately it is noted in as many as 50% of patients. The incidence of initial pain is lower than that of brachial plexopathy. This pain is described in varying terms, such as aching, burning, pulling, cramping, and lancinating; however, pain rarely is a major problem.
• Weakness is asymmetrical. At the height of illness, the ratio of bilateral to unilateral illness is 5:1. Acute lower extremity paralysis has been noted in a patient with cervical cancer 10 weeks after completion of radiation treatment.⁴
• Sensory loss occurs in 50-75% of patients and is more severe with greater motor impairment, which can add significantly to disability.
• Bladder or bowel incontinence may occur.⁵

Physical

• In radiation-induced lumbosacral plexopathy, motor deficits in the lower extremities commonly are bilateral (80%) and asymmetrical. Diffuse limb weakness with distal predominance in L5-S1 distribution is relatively common (55% of patients). Exclusive proximal paresis in the distribution of L2-L4 is less common (10% of patients), as is femoral neuropathy (5% of patients). Moderate weakness is present in 50% of patients, with equal distribution of mild and severe weakness.
• Deep tendon reflexes (DTRs) almost always are abnormal at the knees and/or ankles and usually are present bilaterally.
• Sensory impairments are present in most patients (75%) and more often are bilateral. No specific sensory modality is favored. The distal lower extremities are affected more commonly than are the proximal lower extremities. Impaired deep sensation occurs with severe, superficial sensory loss.
• Skin changes may be present in areas of radiation portals.

Causes

Radiation dosage, treatment technique, and concomitant use of chemotherapy are associated with development of radiation-induced lumbosacral plexopathy.

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