Nerve Root Disorders
(See also Overview of Peripheral Nervous System Disorders.)
Nerve root disorders (radiculopathies) are precipitated by acute or chronic pressure on a nerve root in or adjacent to the spinal column (see figure Spinal nerve roots).
The most common cause is
Less commonly, carcinomatous meningitis causes patchy multiple root dysfunction. Rarely, spinal mass lesions (eg, epidural abscesses and tumors, spinal meningiomas, neurofibromas) may manifest with radicular symptoms instead of the usual symptoms of spinal cord dysfunction.
Diabetes can cause a painful thoracic or extremity radiculopathy by causing ischemia of the nerve root.
Infectious disorders, such as those due to mycobacteria (eg, tuberculosis [TB]), fungi (eg, histoplasmosis), or spirochetes (eg, Lyme disease, syphilis), sometimes affect nerve roots. Herpes zoster infection usually causes a painful radiculopathy with dermatomal sensory loss and characteristic rash, but it may cause a motor radiculopathy with segmental weakness and reflex loss. Cytomegalovirus-induced polyradiculitis is a complication of AIDS.
Radiculopathies tend to cause characteristic radicular syndromes of pain and segmental neurologic deficits based on the cord level of the affected root (see table Symptoms of Common Radiculopathies by Cord Level). Muscles innervated by the affected motor root become weak and atrophy; they also may be flaccid with fasciculations. Sensory root involvement causes sensory impairment in a dermatomal distribution. Corresponding segmental deep tendon reflexes may be diminished or absent. Electric shock–like pains may radiate along the affected nerve root’s distribution.
Symptoms of Common Radiculopathies by Cord Level
Pain may be exacerbated by movements that transmit pressure to the nerve root through the subarachnoid space (eg, moving the spine, coughing, sneezing, doing the Valsalva maneuver).
Lesions of the cauda equina, which affect multiple lumbar and sacral roots, cause radicular symptoms in both legs and may impair sphincter and sexual function.
Findings indicating spinal cord compression include the following:
Radicular symptoms require MRI or CT of the affected area. Myelography is needed only if MRI is contraindicated (eg, because of an implanted pacemaker or presence of other metal) and CT is inconclusive. The area imaged depends on symptoms and signs; if the level is unclear, electrodiagnostic tests should be done to localize the affected root, but they cannot identify the cause.
If imaging does not detect an anatomic abnormality, cerebrospinal fluid analysis is done to check for infectious or inflammatory causes, and fasting plasma glucose is measured to check for diabetes.
Specific causes of nerve root disorders are treated.
Acute pain requires appropriate analgesics (eg, acetaminophen, nonsteroidal anti-inflammatory drugs [NSAIDs], sometimes opioids). NSAIDs are particularly useful for disorders that involve inflammation. Muscle relaxants, sedatives, and topical treatments rarely provide additional benefit. If symptoms are not relieved with nonopioid analgesics, corticosteroids can be given systemically or as an epidural injection; however, analgesia tends to be modest and temporary. Methylprednisolone may be given, tapered over 6 days, starting with 24 mg orally once a day and decreased by 4 mg a day.
Management of chronic pain can be difficult; acetaminophen and NSAIDs are often only partly effective, and chronic use of NSAIDs has substantial risks. Opioids have a high risk of addiction. Tricyclic antidepressants and antiseizure drugs may be effective, as may physical therapy and consultation with a mental health practitioner. For a few patients, alternative medical treatments (eg, transdermal electrical nerve stimulation, spinal manipulation, acupuncture, medicinal herbs) may be tried if all other treatments are ineffective. If the pain is intractable, surgical decompression may be necessary.
Suspect a nerve root disorder in patients who have segmental deficits such as sensory abnormalities in a dermatomal distribution (eg, pain, paresthesias) and/or motor abnormalities (eg, weakness, atrophy, fasciculations, hyporeflexia) at a nerve root level.
If patients have a sensory level, bilateral flaccid weakness, and/or sphincter dysfunction, suspect spinal cord compression.
If clinical findings suggest radiculopathy, do MRI or CT.
Use analgesics and sometimes corticosteroids for acute pain, and consider other drugs and other treatments, as well as analgesics, for chronic pain.