Porth's Essentials of Pathophysiology, 4e

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Nervous System

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polyneuropathy), and metabolic diseases (e.g., diabetes mellitus, uremia). Different causes tend to affect axons of different diameters and to affect sensory, motor, or autonomic neurons to different degrees. Guillain-Barré Syndrome. Guillain-Barré syndrome is an acute life-threatening polyneuropathy. 21–24 The syn- drome defines a clinical entity that is characterized by rapidly progressive limb weakness and loss of tendon reflexes. It has been described as the most common cause of acute, flaccid paralysis in developed countries of the world, now that poliomyelitis has been eliminated. As a syndrome, there are several subtypes of the disor- der, including pure motor axonal degeneration, axonal degeneration of both motor and sensory nerves, and a variant characterized by ophthalmoplegia (paralysis of eye muscles), ataxia (unsteady gait), and areflexia (lack of reflexes). Guillain-Barré syndrome is thought to be an acute onset immune-mediated demyelinating neuropathy. Approximately two thirds of patients report having had an acute, influenza-like illness before the onset of symp- toms. 18 Controlled epidemiologic studies have linked it to infection with Campylobacter jejuni, cytomegalovi- rus, Epstein-Barr virus, and mycoplasma pneumoniae. A C. jejuni infection is often an antecedent to symptoms. In a few cases, the patient reports receiving a vaccina- tion prior to onset of Guillain-Barré syndrome. The disorder is characterized by progressive ascend- ing muscle weakness of the limbs, producing a sym- metric flaccid paralysis. Symptoms of paresthesia and numbness often accompany the loss of motor function. The rate of disease progression varies, and there may be disproportionate involvement of the upper or lower extremities. Paralysis may progress to involve the respi- ratory muscles. Autonomic nervous system involve- ment that causes postural hypotension, arrhythmias, facial flushing, abnormalities of sweating, and urinary retention is common. Pain is another common feature of Guillain-Barré syndrome. It is most common in the shoulder girdle, back, and posterior thighs and occurs with even the slightest of movements. Guillain-Barré syndrome usually is a medical emer- gency. There may be a rapid development of respiratory failure and autonomic disturbances that threaten cir- culatory function. Treatment includes support of vital functions and prevention of complications such as skin breakdown and thrombophlebitis. Removing the circu- lating immune complexes via plasma exchange has been shown to decrease morbidity and shorten the course of the disease. 23,24 Treatment is most effective if initiated early in the course of the disease. High-dose intrave- nous immunoglobulin therapy also has proved effective. Approximately 85% of persons with the disease achieve a full and spontaneous recovery within 6 to 12 months. 21 Back Pain and Spinal Nerve Root Disorders The spinal cord and spinal nerve roots are locatedwithin the vertebral canal. The anterior portion of the spine consists of cylindrical vertebral bodies separated by

intervertebral disks and held together by the anterior and posterior longitudinal ligaments (Fig. 36-9A). The posterior portion of the spine consists of the vertebral arches, each consisting of paired transverse processes, one posterior spinous process, and two superior artic- ular facets. The functions of the posterior spine are to protect the spinal cord and nerves within the spinal canal and to stabilize the spine by providing sites for the attachment of muscles and ligaments. Back pain is a common problem that affects an esti- mated two thirds of people at least once in their life- time. 25 It can result from a number of causes, including problems involving the vertebrae and intervertebral joints or back muscles and ligaments, as well as dis- orders of the spinal nerve roots. Perhaps the most common causes are musculoligamentous injuries and age-related degenerative changes in the intervertebral disks and facet joints. 26 Other causes include spinal nerve root compression due to intervertebral disk her- niation and narrowing of the central canal due to spi- nal stenosis. Pain-sensitive structures in the spine include the periosteum of the vertebrae, dura, facet joints, annulus fibrosus of the intervertebral disk, and posterior longi- tudinal ligament. Pain sensation is conveyed through afferent fibers in the spinal nerves. Local pain is caused by stretching of pain-sensitive structures that compress or irritate sensory nerve endings. Pain referred to the back may arise from abdominal or pelvic structures. Pain associated with muscle spasm is usually dull, and often accompanied by abnormal posture and stiff para- spinal muscles. Nerve root injury (radiculopathy) is a common cause of neck, arm, low back, and leg pain. The pain is typi- cally sharp and radiates to the arm or leg within the ter- ritory of the spinal root. Disorders affecting the upper lumbar segments tend to be referred to the lumbar area, groin, or anterior thigh; and those affecting the lower lumbar and upper sacral segments, to the buttocks and posterior thighs. Diagnosis and Treatment. Although back problems are commonly attributed to a herniated disk, most acute back disorders are caused by less-serious prob- lems. 18,25–28 The diagnostic challenge is to identify those persons who require further evaluation for more seri- ous problems such as malignancies, compression frac- tures, and vascular disorders. The diagnostic measures used in the evaluation of back pain include history and physical examination, including a thorough neurologic examination. Other diagnostic methods may include radiographs of the back and magnetic resonance imag- ing (MRI). Treatment of back pain usually is conservative and consists of analgesic medications, muscle relaxants, and instruction in the correct mechanics for lifting and methods of protecting the back. Pain relief is usually provided using nonsteroidal anti-inflammatory drugs. Muscle relaxants may be used on a short-term basis. Bed rest, once the mainstay of conservative therapy, is now understood to be ineffective for acute back pain.