Merck Manual

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Peter J. Moley

, MD, Hospital for Special Surgery

Last full review/revision Nov 2020
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Sciatica is pain along the sciatic nerve. It usually results from compression of lumbar nerve roots in the lower back. Common causes include intervertebral disk herniation, osteophytes, and narrowing of the spinal canal (spinal stenosis). Symptoms include pain radiating from the buttocks down the leg. Diagnosis sometimes involves MRI or CT. Electromyography and nerve conduction studies can identify the affected level. Treatment includes symptomatic measures and sometimes surgery, particularly if there is a neurologic deficit.

Etiology of Sciatica

Sciatica is typically caused by nerve root compression, usually due to intervertebral disk herniation Herniated Nucleus Pulposus Herniated nucleus pulposus is prolapse of an intervertebral disk through a tear in the surrounding annulus fibrosus. The tear causes pain due to irritation of sensory nerves in the disk, and... read more Herniated Nucleus Pulposus , bony irregularities (eg, osteoarthritic osteophytes, spondylolisthesis Spondylolisthesis Spondylolisthesis is slippage of a lumbar vertebra in relation to the vertebra below it. Anterior slippage (anterolisthesis) is more common than posterior slippage (retrolisthesis). Spondylolisthesis... read more Spondylolisthesis ), spinal stenosis Lumbar Spinal Stenosis Lumbar spinal stenosis is narrowing of the lumbar spinal canal compresses the nerve rootlets and nerve roots in the cauda equina before their exit from the foramina. It causes positional back... read more Lumbar Spinal Stenosis , or, much less often, intraspinal tumor Spinal Cord Tumors Spinal cord tumors may develop within the spinal cord parenchyma, directly destroying tissue, or outside the cord parenchyma, often compressing the cord or nerve roots. Symptoms can include... read more or abscess. Compression may occur within the spinal canal or intervertebral foramen. The nerves can also be compressed outside the vertebral column, in the pelvis or buttocks. L5-S1, L4-L5, and L3-L4 nerve roots are most often affected (see table Motor and Reflex Effects of Spinal Cord Dysfunction by Segmental Level Motor and Reflex Effects of Spinal Cord Dysfunction by Segmental Level Spinal cord disorders can cause permanent severe neurologic disability. For some patients, such disability can be avoided or minimized if evaluation and treatment are rapid. The spinal cord... read more ).

Symptoms and Signs of Sciatica

In patients with sciatica, pain radiates along the course of the sciatic nerve (symptoms related to nerve roots L4, L5, and S1), most often down the buttocks and posterior aspect of the leg to below the knee. The pain is typically burning, lancinating, or stabbing. It may occur with or without low back pain. The Valsalva maneuver or coughing may worsen pain due to disk herniation. Patients may complain of numbness and sometimes weakness in the affected leg.

Nerve root compression Spinal Cord Compression Various lesions can compress the spinal cord, causing segmental sensory, motor, reflex, and sphincter deficits. Diagnosis is by MRI. Treatment is directed at relieving compression. (See also... read more Spinal Cord Compression can cause sensory, motor, or, the most objective finding, reflex deficits. L5-S1 disk herniation may affect the ankle jerk reflex; L3-L4 herniation may affect the knee jerk.

Straight leg raising may cause pain that radiates down the leg when the leg is slowly raised above 60° and sometimes less. This finding is sensitive for sciatica; pain radiating down the affected leg when the contralateral leg is lifted (crossed straight leg raising) is more specific for sciatica. The straight leg raise test can be done while patients are seated with the hip joint flexed at 90°; the lower leg is slowly raised until the knee is fully extended. If sciatica is present, the pain in the spine (and often the radicular symptoms) occurs as the leg is extended. The slump test can also be done, similarly to the straight leg raise test, but with the patient "slumping" (with the thoracic and lumbar spines flexed) and the neck flexed. The slump test is more sensitive, but less specific, for disk herniation than the straight leg raise test.

Diagnosis of Sciatica

  • Clinical evaluation

  • Sometimes MRI, electrodiagnostic studies, or both

Sciatica is suspected based on the characteristic pain. If it is suspected, strength, reflexes, and sensation should be tested. If there are neurologic deficits or if symptoms persist for > 6 weeks, imaging and electrodiagnostic studies should be done. Structural abnormalities causing sciatica (including spinal stenosis) are most accurately diagnosed by MRI or CT.

Electrodiagnostic studies can confirm the presence and degree of nerve root compression and can exclude conditions that may mimic sciatica, such as peroneal nerve palsy, multiple mononeuropathy Multiple Mononeuropathy Multiple mononeuropathies are characterized by sensory disturbances and weakness in the distribution of ≥ 2 affected peripheral nerves. (See also Overview of Peripheral Nervous System Disorders... read more , or polyneuropathy Polyneuropathy A polyneuropathy is a diffuse peripheral nerve disorder that is not confined to the distribution of a single nerve or a single limb and typically is relatively symmetrical bilaterally. Electrodiagnostic... read more . These studies may help determine whether the lesion involves single or multiple nerve levels and whether the clinical findings correlate with MRI abnormalities (especially valuable before surgery). However, abnormalities may not be evident on electrodiagnostic studies for up to a few weeks after symptoms begin.

Treatment of Sciatica

  • Activity as tolerated, analgesics, and sometimes drugs that relieve neuropathic pain

  • Physical therapy

  • Sometimes oral or epidural corticosteroids

  • Surgery for severe cases

Acute pain relief from sciatica can come from 24 to 48 hours of bed rest in a recumbent position with the head of the bed elevated about 30° (semi-Fowler position). Measures used to treat low back pain, including nonopioid analgesics (eg, NSAIDs, acetaminophen), can be tried for up to 6 weeks. Drugs that decrease neuropathic pain (see Drugs for Neuropathic Pain Treatment Neuropathic pain results from damage to or dysfunction of the peripheral or central nervous system, rather than stimulation of pain receptors. Diagnosis is suggested by pain out of proportion... read more ), such as gabapentin or other anticonvulsants or low-dose tricyclic antidepressants (no tricyclic is superior to another), may relieve symptoms. Oral gabapentin 100 to 300 mg at bedtime is used initially and should be titrated up slowly to avoid adverse effects that might inhibit patient recovery. As with all sedating drugs, care should be taken in older patients, patients at risk of falls, patients with arrhythmias, and those with chronic kidney disease.

  • Muscular weakness that is worsening or not resolving

  • Other progressive neurologic deficits

  • Intolerable, intractable pain that interferes with job or personal functions in an emotionally stable patient and that has not lessened after 6 weeks of conservative treatment

Classic diskectomy with limited laminotomy for intervertebral disk herniation is the standard procedure. If herniation is localized, microdiskectomy may be done; with it, the skin incision and laminotomy can be smaller. Chemonucleolysis, using intradiskal injection of chymopapain, is no longer used.

Predictors of poor surgical outcome include

  • Prominent psychiatric factors

  • Persistence of symptoms for > 6 months

  • Heavy manual labor

  • Prominence of back pain (nonradicular)

  • Secondary gain (ie, litigation and compensability)

Key Points

  • Sciatica is typically caused by nerve root compression, usually due to intervertebral disk herniation, osteoarthritic osteophytes, spinal stenosis, or spondylolisthesis.

  • Classically, burning, lancinating, or stabbing pain radiates along the course of the sciatic nerve, most often down the buttocks and posterior aspect of the leg to below the knee.

  • Loss of sensation, weakness, and reflex deficits can occur.

  • Do MRI and electrodiagnostic studies if there are neurologic deficits or symptoms persist for > 6 weeks.

  • Conservative treatment is usually sufficient, but consider surgery for disk herniation with a progressive neurologic deficit, or persistent, intractable pain.

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