Spinal Cord Disorders

Published on 06/06/2015 by admin

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Last modified 06/06/2015

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80 Spinal Cord Disorders

Disorders of the spinal cord are exceedingly diverse. They range in etiology from congenital malformation to neurodegenerative, inflammatory, infectious, ischemic, and traumatic. The spinal cord functions as the primary communication between the brain and the body. Disorders of the spinal cord, termed myelopathies, typically conform to neuroanatomic pathways and vascular territories, resulting in classic neurologic syndromes. Acute myelopathies require urgent attention. Profound physical disability may result.

Etiology and Pathogenesis

According to the Centers for Disease Control and Prevention, spina bifida, the most common neural tube defect, occurs at a rate of two in 10,000 live births and results in varying degrees of disability from clinically normal to paraplegia. Traumatic spinal cord injury occurs at a rate of about 40 cases per million people per year and annually costs $9.7 billion in health care costs. Of these cases, it is estimated that up to half occur in adolescence and young adulthood. To diagnose and treat the disorders of the spinal cord, an understanding of its anatomy and how to examine for dysfunction of the spinal cord is imperative. The spinal cord is divided into four sections: cervical, thoracic, lumbar, and sacral (C, T, L, and S). It terminates at vertebral body level L2–L3 in infants, and in grown children and adults, it terminates at level L1–L2, where the cauda equina, the collection of nerves exiting the cord, begins. The spinal cord itself is sectioned in to a central H-shaped region of gray matter and surrounding white matter tracts (Figure 80-1).

The anterior horn of the gray matter contains motor nuclei, which receive information from the descending motor tracts. The axons of the motor neurons leave the ventral horn via the ventral root and synapse at the neuromuscular junction. The dorsal horn of the gray matter processes sensory information. It contains afferents from muscle spindles that participate in spinal cord reflexes. It also contains second-order neurons that mediate the various sensory inputs from the body.

There are three major white matter tracts of clinical importance when assessing myelopathy. The major descending tract is the lateral corticospinal tract (located posterolaterally within the cord). This tract contains the upper motor neurons originating from the primary motor cortex. The descending fibers cross at the cervicomedullary junction and descend, innervating the side of the body opposite the cortex. Within the tract, fibers that carry information to the upper extremities are located medially, and fibers that control the lower extremity movement are located laterally. The dorsal columns contain ascending proprioceptive and vibratory information and decussate in the medulla. These fibers are arranged so that information from the upper body is carried most laterally, in the fasciculus cuneatus, and that from the lower half is most medially, in the fasciculus gracilis. The spinothalamic tract (located anterolaterally in the cord) carries pain, temperature, and crude touch sensory information. These tracts decussate within a few levels of entering the spinal cord; therefore, they contain primarily contralateral sensory information. Within the spinothalamic tract, upper body information is carried medially, and lower body information is carried laterally.

The vascular anatomy of the spinal cord is divided into anterior and posterior circulations, arising from the vertebral arteries in the neck. The anterior spinal artery supplies the anterior two-thirds of the spinal cord. The two posterior spinal arteries primarily supply the posterior columns.

Clinical Presentation and Differential Diagnosis

The clinical examination is extremely helpful in localizing lesions within the spinal cord and can help determine the pathophysiology of spinal cord disease depending on the pattern of deficits. When examining a patient with suspected spinal cord disease, a thorough history and neurologic examination are essential to localizing the problem and generating a differential diagnosis. Cranial nerve examination can be helpful in distinguishing pure spinal cord disease from disease that involves the brainstem as well. It is important to perform a detailed motor, coordination, and reflex examination, including muscle bulk tone and strength, to determine patterns of weakness and elicit upper and lower motor neuron signs. Upper motor neuron signs include weakness, hypertrophy, spasticity, hyperreflexia, clonus, and a positive Babinski’s sign. Lower motor neuron signs include weakness, flaccidity, atrophy, fasciculations, and hyporeflexia. Tenderness along the spine can help with localization, and a sensory examination should detail the pattern of reported sensory loss and always include sensory level elicited by determining pinprick sensation and light touch along both sides of the spinal cord. Assessment of rectal tone and bowel and bladder function is critical. Respiratory function should be evaluated with vital capacity and negative inspiratory force. Importantly, an acute spinal cord lesion can present with signs of “spinal shock,” which includes reduced tone (or flaccidity in the extreme situation), hyporeflexia distal to the lesion, and reduced rectal sphincter tone. Only later will the upper motor neuron signs evolve. The sensory examination takes on greater emphasis toward localizing a spinal cord lesion in the acute setting.

There are common patterns of motor and sensory involvement depending on the localization of disease within the spinal cord. Table 80-1 describes the features of some typical patterns or spinal cord disease and their common causes (Figure 80-2).

Table 80-1 Features of Typical Patterns or Spinal Cord Disease and Common Causes

Localization Common Pattern of Weakness and Sensory Loss Common Causes in Pediatric Patients
Cervical spinal cord
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