Introduction
Myelopathy is a clinical syndrome caused by spinal cord dysfunction. Practitioners across different specialties from emergency medicine to trauma surgery, to neurology, to internal medicine encounter patients with myelopathy. Despite being anatomically small, the spinal cord can be pathologically affected by many disease etiologies, which often leads to uncertainty about the appropriate steps for diagnosis, investigation, and treatment. In this chapter, the clinical syndrome of myelopathy and then the specific causes of spinal cord disease will be reviewed.
Anatomical Structure
Anatomically, the spinal cord starts at the cranio-cervical traction and descends to about the L1 level. The spinal cord is surrounded by the bony vertebral column and descends through the vertebral canal. Motor nerve roots exit the spinal cord ventrally, while sensory nerve roots enter the spinal cord in the dorsal or posterior aspect ( Fig. 17.1 ). The motor and sensory nerve roots combine at the level of the intervertebral foramina to exit as spinal nerves. In the spinal cord, gray matter (containing neuronal cell bodies) is located centrally. Ascending and descending white matter tracts surround the central gray matter.
While many tracts exist in the spinal cord ( Fig. 17.2 ), for the practicing clinician, three of these white matter projections are especially significant for localization of injury.
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Lateral corticospinal tract: In the spinal cord the corticospinal tract is located laterally and provides mostly ipsilateral control of motor neurons.
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Posterior or dorsal columns: These white matter tracts are located dorsally in the spinal cord and mediate ipsilateral perception of vibration and joint position sense.
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Spinothalamic tracts: These tracts are located anterolaterally and conduct contralateral perception of pain and temperature.
Note that, for the sensory tracts, the distinction between the different types of sensation and their pathways is not exclusive. Touch sensation, for example, is conducted through both dorsal columns and spinothalamic tracts. The spinal cord is especially important for control of autonomic functions such as bladder or bowel sphincter control. These essential tracts are located centrally. The upper cervical spinal cord is also critical for controlling respiratory function (through innervation of the diaphragm by the phrenic nerves).
The vascular supply of the spinal cord differs between the anterior and posterior aspects. The anterior two-thirds of the spinal cord, including the corticospinal tracts and the spinothalamic tracts, are supplied by the anterior spinal artery. Posteriorly, there are paired posterior spinal arteries that supply the posterior columns. The spinal arteries form an anastomotic network that is reinforced through radiculomedullary arteries (segmental arteries that enter through the spinal intervertebral foramen and end in the spinal cord). One of the largest feeder arteries for the anterior spinal artery is the Artery of Adamkiewicz. Venous drainage of the spinal cord is through both segmental radicular veins and through longitudinal channels.
Clinical Syndrome
Myelopathy is a clinical diagnosis, and ascertaining consistent symptoms and signs are key to the diagnosis. Common symptoms of spinal cord dysfunction are bilateral weakness in the arms or legs, gait disorder especially described as stiff and slow, numbness with paresthesia, urinary urgency or hesitancy, and bowel sphincter dysfunction. These symptoms are, however, not specific for spinal cord dysfunction and, hence, can be missed. For example, weakness in the legs can also potentially be caused by a brain lesion or from compression of lumbosacral nerve roots. There are some symptoms that are more indicative of spinal cord dysfunction. Many patients with spinal cord disease experience a band of tightness across the trunk that is often described as a plastic wrap or a squeezing sensation. This sense is typically circumferential across the trunk. The authors have met many patients who were brought to the emergency room with a concern about cardiac ischemia because of the tightness across the chest from a thoracic cord lesion.
Neurological examination provides more specificity to the diagnosis of myelopathy. Injury to the corticospinal tracts causes the upper motor neuron syndrome of weakness, spasticity, and increased deep tendon stretch reflexes. In acute spinal cord injury, there is usually flaccid paralysis that gradually converts over the space of days to weeks to spastic weakness. Neurological examination generally discloses sensory loss to different sensory modalities when the spinothalamic and dorsal columns are affected. There are patterns to the neurological examination that are especially suggestive of spinal cord dysfunction:
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Lhermitte sign : With the patient in a sitting position, the examiner flexes the neck forward to elicit electric sensation down the spine or into the arms. When flexing the neck forward, simultaneously flexing the hips can improve the sensitivity of the technique ( Fig. 17.3 ).
Figure 17.3
The Lhermitte sign is elicited by having the patient sitting (A) and then flexing the neck forward (B). Flexing the hip shown in B can further improve sensitivity of the sign.
From Orthopedic Physical Assessment , Chapter 3, 164–242.e6.
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Sensory level: Sensation to pinprick, light touch, or temperature is best assessed at specific dermatome levels ( Fig. 17.4 ). A sensory level is defined as the most caudal level at which both pinprick and light touch are preserved. The sensory level can be different on either side of the body. For example, sensory level on the right side can be at the T10 level (at the level of navel) while being T4 level on the left (at the level of the nipple line). Anatomically, the spinal cord lesion does not have to be at the same location as the clinical sensory level. In the prior example of T10 sensory level on the right and T4 sensory level on the left, the causative spinal cord lesion can potentially be in the cervical spinal cord. The sensory level indicates that the spinal cord lesion could be present at that level or at a level above.
Figure 17.4
Dermatomes on the anterior surface of the body. Note that after C4 dermatome, the rest of the cervical dermatomes are represented in the arms.
From Lee J, Thumbikat P. Pathophysiology, presentation and management of spinal cord injury. Surgery . 2015;33(6):238–247.Related posts:
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