Spinal Shock

Spinal shock refers to the period of depressed spinal reflexes caudal to an acute spinal cord injury; it is followed by emergence of pathological reflexes and return of cutaneous and muscle stretch reflexes (Ditunno et al., 2004). During the acute phase of spinal shock, paralysis of muscles, sensory impairment, and loss of autonomic function are present below the level of injury. Commonly, the first reflex to appear after a clinically complete spinal cord injury is the delayed plantar response. It is induced by stroking the plantar surface of the foot with a blunt instrument upward from the heel, along the lateral surface, and across the metatarsal heads. A delayed response consists of plantar flexion of the great toe and other toes, often detectable within the first hours after injury. When the delayed plantar response persists for more than 1 week, it is often associated with a severe spinal cord injury and a less favorable prognostic outlook for a significant functional recovery. The return of reflexes over days and weeks after the initial period of spinal shock appears to follow a general pattern, with cutaneous reflexes recovering before muscle stretch reflexes. Specifically, the bulbocavernosus and cremasteric reflexes commonly return before the ankle jerk, Babinski sign, and knee jerk.

Incomplete Lesions of the Spinal Cord

Central Cord Syndrome

Traumatic central cord syndrome is commonly characterized by the triad of (1) motor impairment that is disproportionately more severe in the upper than the lower extremities, (2) bladder dysfunction that usually includes urinary retention, and (3) sensory dysfunction of varying degrees. An international consensus group recently suggested that an upper- and lower-extremity difference of at least 10 motor score points, based on the Medical Research Council scale, can be considered as a quantitative addition to the commonly used qualitative criteria for making the diagnosis (van Middendorp et al., 2010). An additional clinical feature of the traumatic central cord syndrome is a dissociated sensory loss for pain and temperature, whereas vibration and position sense remain preserved. This sensory presentation may be explained by a direct injury to intramedullary decussating fibers, which normally would ascend contralaterally as part of the spinothalamic tract. As a result, a capelike sensory deficit may be encountered in patients with a cervical level injury, but sensation within more caudal dermatomes would generally be spared (Fig. 24.3).

Fig. 24.3 Magnetic resonance image of the cervical spine showing a contrast-enhancing mass. Patient presented with a capelike sensory loss for pain and temperature. Resection of the mass revealed a glioma.

A traumatic central cord syndrome is mostly encountered in elderly patients who have suffered a relatively minor trauma in the form of a cervical hyperextension injury, commonly in the setting of an underlying cervical spondylosis. Falls and motor vehicle injuries are common etiologies. Syringomyelia or tumors may also produce a central cord syndrome.

Foramen Magnum and Upper Cervical Spine

When structural lesions are located in or adjacent to the foramen magnum, several different neurological patterns are possible. For example, brainstem signs may occur together with symptoms from a spinal cord injury. Involvement of the lower portion of the brainstem is suggested by speech impairments, including dysarthria and dysphonia, as well as by dysphagia. In addition, facial numbness and nystagmus may be detected in association with tumors or other structural lesions in the foramen magnum. When compression of the spinal cord occurs, long-tract signs may present from injury to the corticospinal tract with, for instance, a spastic hemiparesis or quadriparesis. A lower motor neuron injury component may also be detectable from lesions at the craniocervical junction and the foramen magnum, with upper extremity weakness, muscular atrophy, and decreased muscle stretch reflexes.

Several pathological processes and lesions may be present at the level of the foramen magnum and its immediate vicinity. These conditions include Arnold-Chiari malformations; traumatic injuries; rheumatoid arthritis; syringomyelia; vascular lesions such as thrombosis, dissection, or arteriovenous malformation; and a variety of tumors including meningiomas. Multiple sclerosis may also cause intramedullary lesions of the brainstem and the upper cervical spinal cord and selectively affect long white-matter tracts. Imaging studies, especially MRI, help determine the nature and precise anatomical location for pathological processes in the foramen magnum and upper cervical spine region.

Lesions affecting the uppermost portion of the cervical spine may be challenging to diagnose owing to a nonlocalizing symptom complex upon initial presentation. Pain is a common early symptom and may be localized to the neck or occipital region. At times, the pain may be aggravated by neck movement. When upper cervical nerve roots are compressed, a radicular pain may present in the corresponding dermatome. Irritation of the second cervical nerve root, for example, may present with a pain localized within the posterior aspect of the scalp, whereas an injury to the third and fourth nerve roots may induce pain that is projected to the neck or shoulder. A lower motoneuron injury presentation with upper extremity muscular weakness and atrophy may also be part of the clinical presentation. When the spinal cord is compressed by epidural or subdural space-occupying lesions, spastic weakness of upper and lower extremities typically follow.

An injury or disease process affecting the upper cervical spinal cord may also compromise breathing. Normal respiration requires functional use of the diaphragm muscle, which is innervated by the phrenic nerve. Motoneurons contributing to the phrenic nerve are located within the cervical spinal cord and contribute efferent axons to the C3-C5 ventral roots. Therefore, complete injuries affecting the spinal cord above the C3 segment will compromise the function of the diaphragm, and respiratory failure may follow.

Lower Cervical and Upper Thoracic Spine

Injuries to the lower part of the cervical spine and upper thoracic spine may be caused by extramedullary compression of nerve roots and the spinal cord or by an intramedullary disease process. The correlation between presenting symptoms and localization of the underlying lesion is most precise for the extramedullary pathological processes (e.g., tumors, herniated disks) that compress individual segmental nerve roots or spinal nerves. Intramedullary lesions may also present with pain, but the segmental localization is commonly less precise.

Extramedullary lesions typically first irritate segmental nerve roots and the spinal nerve, with radicular pain and sensory deficits typically following the corresponding dermatomal distribution. Similarly, motor deficits involve each myotome affected by the lesion. Muscle stretch reflexes may also provide helpful information with regard to the primary level of injury, as the affected segmental reflex is typically depressed or absent, and caudal reflexes are hyperactive. For instance, when a lesion is at the C4-C6 level, a radicular pattern of pain and sensory symptoms may typically involve the radial side of the arm, forearm, and hand. Motor deficits include weakness in elbow flexion. In addition, the biceps and brachioradialis muscle stretch reflexes may be depressed or absent, especially when the C5-C6 levels are involved.

In contrast, lesions at the C7-T1 level usually present with pain and sensory impairments over the ulnar side of the upper extremity, including the arm, forearm, and hand. Motor deficits related to affected myotomes commonly involve elbow extension, the intrinsic hand muscles, and the triceps reflex.

Lower and upper motoneuron signs may also be present in adjacent segments. If segmental nerve roots and the spinal cord are compressed by a herniated disk or space-occupying lesion at the C5-C6 level, for example, a decreased brachioradialis reflex may reflect a C6 radiculopathy, whereas a brisk and hyperactive finger flexor reflex reflects an upper motoneuron syndrome.

Thoracic Levels

Traumatic spinal cord injury at the thoracic level usually produces a complete lesion. The segmental level of injury is best determined by a careful sensory examination of dermatomes (Maynard et al., 1997). Useful clinical landmarks are the nipple line for the T4 dermatome and the umbilicus for the T10 dermatome. Pain may follow a radicular pattern around the chest or abdomen, corresponding to the segmental levels of injury. Sensory testing of pin, temperature, pressure, and light touch appreciation may determine the most caudal dermatome of normal sensation, as well as a zone of partial preservation. The sensory testing should include evaluation of dermatomes of the left and right side of the body, with comparisons of homologous levels. In addition to a combination of at-level pain, sensory deficits, and muscular weakness, autonomic dysfunction may develop from long-tract involvement and include urinary retention, bladder-sphincter dyssynergia, and bladder hyperreflexia.

Conus Medullaris and Cauda Equina

The conus medullaris of the spinal cord terminates approximately at the level of the L1 vertebra, although the precise location of the tip of the conus may show marked variability among subjects. This anatomical aspect of the spinal cord is important because spine trauma commonly takes place at the thoracolumbar junction, and the extent of such injuries is highly variable (Kingwell et al., 2008). Traumatic injuries to the conus medullaris usually result in weakness or paralysis of the lower extremities, absence of lower-extremity reflexes, and saddle anesthesia (Fig. 24.4). However, some patients with conus medullaris injuries exhibit a mixed upper and lower motoneuron syndrome. In contrast, a cauda equina injury that lesions lumbosacral roots below the level of the conus medullaris is a pure lower motoneuron syndrome. Cauda equina injuries present with lower-extremity weakness, areflexia and decreased muscle tone, and variable sensory deficits. At least a third of these patients suffer considerable central pain. Affected limb and pelvic floor muscles develop flaccid weakness, and electromyography shows denervation after either a conus medullaris or cauda equina injury, especially following anatomically complete lesions.

Fig. 24.4 Magnetic resonance imaging demonstrating the effects of trauma to the thoracolumbar portion of the spine with a crush injury of the cauda equina (CE) and conus medullaris (CM) portion of the spinal cord. Note T12/L1-level spine fracture and dislocation.

Both conus medullaris and cauda equina injuries are associated with bladder, bowel, and sexual dysfunction (Pavlakis et al., 1983). Urodynamic evaluations typically demonstrate detrusor areflexia, and a rectal exam identifies a flaccid anal sphincter. In addition, the bulbocavernosus reflex is typically absent or diminished, and reflexogenic erection in males is commonly lost.

Imaging studies (e.g., plain radiographs, CT, MRI) identify structural pathology. Burst fractures and fracture dislocations are common injuries to the spinal column that result in neurological deficits suggesting a conus medullaris or cauda equina involvement. Following trauma to the thoracolumbar spine, imaging studies can be used to assess spinal stability and identify detailed aspects of spine fractures, including the presence and location of bone fragments, spinal canal encroachment, epidural hematomas, and herniated discs. A variety of treatment options exist (e.g., surgical stabilization of the spine, decompression of the conus medullaris and nerve roots).

A lumbar spinal stenosis due to a congenitally small-diameter spinal canal or central disk and spondylotic narrowing one or more levels below L1 may present with a subtle course. Over months to years, lower-extremity numbness or pain, usually in an L3-S1 single or multiradicular pattern, accompanies standing and walking, often gradually progressing to limit walking distance. Pain is commonly accompanied by weakness, but patients may not be aware of their deficit. Clinical insight into this diagnosis and level of cauda compression is gained by a manual muscle examination after a few minutes of being supine, followed by having the subject walk for about 500 feet, and then immediately retesting strength. Transient paresis often is found immediately after the walk and resolves within a minute or two.

Pain Syndromes

Pain may originate from irritation, injury, or disease structures associated with the spine and present with a variety of pain syndromes. The symptoms of pain and their diagnostic features depend on the location of spine irritation and involved structures. Distinct pain syndromes may develop as a result of irritation or injury to the vertebral column, ligaments, the dura mater, nerve roots, and spinal cord. Neuropathic pain may take the form of paresthesia (abnormal but not unpleasant sensation that is either spontaneous or evoked), dysesthesia (an abnormal, unpleasant sensation that is spontaneous or evoked), allodynia (pain evoked by ordinary stimuli such as touch or rubbing), and hyperalgesia (an augmented response to a stimulus that is usually painful).

Local Pain

Localized neck or back pain may result from irritation or injury to innervated spine structures including ligaments, periosteum, and dura. The pain is typically deep and aching, may vary with a change in position, and often becomes worse from increased load or weight bearing on affected structures. Percussion or palpation over the spine may in some patients worsen the local pain. When the injured or diseased spine structures are irritated, secondary symptoms may develop and include muscle spasm and a more diffusely located pain.

Projected Pain

Irritation of or injury to the spine and associated structures may result in pain that can be projected to other parts of the body (e.g., a pathological process involving the facet joints may be experienced as pain in an upper or lower extremity). When a nerve root is irritated or injured, the projected pain represents a radicular pain. In contrast, when the spine itself is irritated, a nonradicular pain affecting a remote body part may develop as referred pain. Although both radicular pain and referred pain may be experienced as pain located at some distance from the source, the two forms of projected pain exhibit distinct features that aid diagnosis.

Radicular Pain

Radicular pain commonly has a sharp, stabbing quality and can often be exacerbated by activities that stretch the affected nerve root (e.g., straight leg raising or flexion of the neck). Other activities that may result in additional pressure on a nerve root, such as straining or coughing, may also increase the intensity and severity of radicular pain. Activities that decrease stretching of affected nerve roots, such as flexion of the hip and knee in cases of an S1 radiculopathy, tend to reduce radicular pain and discomfort. In addition to the symptoms of radicular pain, nerve root irritation and injury may also result in sensory and motor deficits following the same dermatome and myotome distribution as the affected nerve root. This helps localize the level of spinal cord injury that is causing paraplegia.

Pain after Spinal Cord Injury

Pain often accompanies injury to the spinal cord. Regardless of segmental level or completeness of injury, most patients with a traumatic spinal cord injury develop a clinically significant pain syndrome at some post-lesion time point (Waxman and Hains, 2006). Neuropathic pain after spinal cord injury may affect different locations. At-level pain affects the portions of the body that are innervated by the injured spinal cord segments. Below-level pain is located in body segments receiving innervation from the spinal cord caudal to the lesioned segments. Above-level pain is less common compared to the other two forms of postinjury pain but, when present, affects body segments innervated by spinal cord segments rostral to the site of spinal cord injury. Musculoskeletal sources of pain and pain with overuse of joints and soft tissues also are frequent but remedial sources of pain.

Pain developing after a spinal cord injury is commonly described as burning, pricking, or aching in quality. It can be experienced as deep or superficial in location. Some patients with spinal cord injury develop a severe and excruciating pain syndrome, which in many cases is difficult to treat and control symptomatically. In some patients, pain may be experienced below the segmental level of injury in body areas exhibiting complete loss of other types of sensation including touch, pressure, and proprioception. In such cases, pain in the lower extremities may be experienced after a thoracic spinal cord injury without noxious stimulation and without the patient being able to discriminate cutaneous or proprioceptive stimuli. The mechanisms for such painful phantom phenomena are not well understood but include dorsal horn, thalamic, and cortical adaptations to ordinary and noxious inputs.

Autonomic Dysreflexia

Injuries to the spinal cord that result in paraplegia from a lesion above T6 may also impair autonomic control and result in episodes of severe hypertension or hypotension (Blackmer, 2003). Autonomic dysreflexia represents an acute syndrome characterized by excessive and uncontrolled sympathetic output from the spinal cord. As a result, the blood pressure is suddenly and markedly elevated. Associated symptoms include headache; malaise; blurring of vision; flushed, sweaty skin above the level of injury; and pale, cool skin below it. An episode of autonomic dysreflexia can be triggered by any noxious stimulation below the segmental level of injury. Common triggers include bladder distension, constipation, rectal fissures, joint injury, and urinary tract infection. Autonomic dysreflexia may present soon after the initial injury but more commonly becomes symptomatic several months after the spinal cord injury. Prevention is the best approach. Treatment of acute symptoms targets removal of noxious stimuli and cautious lowering of the blood pressure.

Bladder Dysfunction

Normal bladder and bowel control depend on segmental reflexes involving both autonomic and somatic motor neurons, as well as descending and ascending tracts of the spinal cord (Fowler et al., 2008). As a result, bladder and bowel function may be impaired after an injury to any segmental level of the spinal cord. Different clinical syndromes develop depending on whether the injury or disease process affects the sacral spinal cord directly or higher segmental levels. Traumatic spinal cord injuries with paraplegia taking place above the T12 vertebra will interrupt spinal cord long-tract connections between supraspinal micturition centers in the brainstem and cerebral cortex and the sacral spinal cord. An upper motoneuron syndrome follows, with detrusor-sphincter dyssynergia caused by impaired coordination of autonomic and somatic motor control of the bladder detrusor and external urethral sphincter, respectively. Incomplete bladder emptying results. In addition, the upper motoneuron syndrome also includes detrusor hyperreflexia with increased pressure within the bladder. In contrast, injury to the T12 vertebra and below results in a direct lesion to the sacral spinal cord and associated nerve roots. A direct lesion to preganglionic parasympathetic neurons and somatic motoneurons of the Onuf nucleus located within the S2-S4 spinal cord segments results in denervation of pelvic targets. Injuries to both the conus medullaris and cauda equina present as a lower motoneuron syndrome characterized by weak or flaccid detrusor function. Urinary retention follows, with risk of overflow incontinence. The goal for all bladder care is to avoid retrograde urine flow, urinary tract infections, and renal failure. Management of both upper and lower motoneuron bladder impairment commonly includes clean intermittent bladder catheterizations. Chapter 38 discusses evaluation and treatment.