Porth's Essentials of Pathophysiology, 4e

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Nervous System

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documentation of herniation by an imaging procedure, consistent pain, or consistent neurologic deficit that failed to respond to conservative therapy. Back Pain Emergencies. Although acute back pain is usually a non–life-threatening condition, in 5% to 10% of persons it is a manifestation of a more serious patho- logic process. 30 Vascular catastrophes (ruptured abdom- inal aortic aneurysms and dissecting aortic aneurysms), malignancy, spinal cord compression syndromes, and infectious processes may all present as acute back pain. Clinical findings, commonly referred to as red flags, that indicate the possibility of more serious dis- ease include gradual onset of pain; age younger than 20 years or older than 50 years; thoracic back pain; history of trauma, fever, chills, night sweats, immu- nosuppression, or malignancy; unintentional weight loss; recent procedure known to cause bacteremia; and history of intravenous drug use. 30 The gradual onset of pain may be indicative of malignancy or infection. Back pain that begins before 20 years of age suggests congenital or developmental disorders, and new-onset pain in persons 50 years of age or older is more likely to be a manifestation of serious conditions such as an aortic aneurysm, malignancy, or compression fracture. Pain that is aggravated by lying down is a red flag for malignancy or infection, and pain that improves with sitting or slight flexion of the spine suggests the pres- ence of spinal stenosis. Persons with symptoms of large or rapidly evolving neurologic deficits require urgent evaluation for possible cauda equina syndrome, epi- dural abscess, or central disk herniation. Signs and symptoms that suggest possible cauda equina syndrome are low back pain associated with bilateral leg weak- ness (from multiple lumbar nerve root compressions), saddle area numbness, bowel and bladder incontinence, or impotence (indicating multiple sacral nerve compres- sions). 25,30 Reports of neurologic symptoms such as par- esthesia, motor weakness, and gait abnormalities also require additional diagnostic tests to rule out spinal cord compression. ■■ Muscular dystrophy is a term used to describe a number of disorders, including Duchenne muscular dystrophy, that produce progressive deterioration of the skeletal muscles. Myasthenia gravis is a disorder of the neuromuscular junction resulting from a deficiency of functional acetylcholine receptors, which causes weakness of the skeletal muscles. ■■ Peripheral nerve disorders, which involve motor and sensory neurons outside the CNS, include the mononeuropathies, such as carpal tunnel syndrome, that involve a single peripheral nerve; SUMMARY CONCEPTS

Nerve root

L4

L5

S1

Pain

Numbness

Extension of quadriceps

Dorsiflexion of great toe and foot

Plantar flexion of great toe and foot

Motor weakness

FIGURE 36-10. Dermatomes of the leg (L1 through S5) where pain and numbness would be experienced with spinal root irritation.

The most common sensory deficits from spinal nerve root compression are paresthesias and numbness, par- ticularly of the leg and foot. Knee and ankle reflexes also may be diminished or absent. A herniated disk must be differentiated from other causes of acute back pain. Diagnostic measures include history and physical examination. Neurologic assess- ment includes testing of muscle strength and reflexes. The straight-leg test is an important diagnostic maneuver. It is done with the person in the supine position and is performed by passively raising the person’s leg. The test can also be done by slowly extending the knee while the person sits on a table, with both hip and knee flexed at 90 degrees. The maneuver is designed to apply traction along the nerve root, which exacerbates pain if the nerve root is acutely inflamed. Normally, it is possible to raise the leg approximately 90 degrees without causing discomfort of the hamstring muscles. The test result is positive if pain is produced when the leg is raised to 60 degrees or less. Other diagnostic methods include radiographs of the back, MRI, computed tomography (CT), and CT myelography. Treatment usually is similar to that for back pain. Surgical treatment may be indicated when there is