Displacement of Thoracic Disc Without Myelopathy
Displacement, Thoracic Intervertebral Disc Without Myelopathy
Displacement of a thoracic intervertebral disc refers to protrusion or herniation of the disc between two adjacent spinal bones (vertebrae) in the mid-back (thoracic spine; vertebrae T1-T12). Discs separate and form a cushion that absorbs shock and allows movement. The discs are composed of an inner gel-like material (nucleus pulposus) and an outer ring of tough, fibrous material (annulus fibrosus). When the disc intrudes into the spinal canal (disc displacement or herniation), it may compress the spinal cord (myelopathy) or spinal nerves.
The thoracic spine is the least common area for disc displacement. Most thoracic disc displacement occurs between vertebrae T9 and T12. Symptomatic thoracic disc herniation is much less common than symptomatic disc herniation in either the neck (cervical spine) or low back (lumbar spine). As in the cervical and lumbar spines, symptom-free (asymptomatic) disc herniations in the thoracic spine are common incidental findings in imaging tests (CT and MRI). Thoracic disc displacement usually results from degeneration as part of normal aging. Thoracic disc displacement due to injury is uncommon due to the protective effect of the rib cage, but in about 37% of cases, there is a history of previous trauma.
Incidence and Prevalence: Symptomatic herniated thoracic discs are rare, accounting for 0.25% to 0.75% of all symptomatic disc herniations; the population incidence is estimated at 1 per million. The incidence of asymptomatic thoracic disc abnormalities is much higher.
Causation and Known Risk Factors
Risk for thoracic disc protrusion is slightly greater in males and in females. Most thoracic disc herniations occur in individuals between the ages of 40 and 60 years old.
History: Important items to note in the history include: information about pain (onset, location, quantity, quality, setting, aggravating and alleviating factors, associated symptoms), axial vs. peripheral pain, and history of mid-back injury. Disc-related pain without nerve root involvement may be vague and diffuse. Radiating (radicular) pain can be dull and aching or sharp and electric; thoracic pain may be absent.
In the absence of a thoracic injury, thoracic disc displacement may be difficult to diagnose. Upper thoracic disc herniation (T2-T5) can be mistaken for cervical disc disease, while lower thoracic disc herniation can mimic lumbar disc disease. Individuals may complain of acute, chronic, or recurrent mid-back (axial) or rib pain. In some cases, the pain may begin abruptly after an injury such as a fall onto the buttocks or landing flat on the feet. Straining for a bowel movement, coughing, or sneezing may aggravate pain. Other symptoms may include muscle weakness (motor), sensory disturbances (e.g., touch), and bowel or bladder dysfunction (15% to 20% of patients. Radiating pain caused by pressure on spinal nerve roots (radicular pain) and sensory loss from nerve root compression follows the distribution of the affected intercostal nerve, which runs between the ribs from the back towards the front of the body at the level of the disc herniation.
Physical exam: Palpation of the affected vertebra may elicit tenderness. Range-of-motion of the entire spine, hips, knees, and ankles should be assessed as well as bilateral straight leg raising. Neurologic examination may reveal deficits such as decreased sensation along the course of a rib. The physician may assess abdominal reflexes, lower extremity reflexes, and sensation.
Tests: Laboratory testing can help to rule out other conditions. Blood tests may include erythrocyte sedimentation rate (ESR) to evaluate inflammation, a complete blood count (CBC) to look for infection or multiple myeloma, rheumatoid factor, and serum protein electrophoresis. Human leukocyte antigens (HLA-B27) may be typed.
X-rays of the thoracic spine may help to exclude tumor and infection. In addition, the x-ray may show congenital or developmental deformities of the spine such as side-to-side curvature (scoliosis) or a hunchback (kyphosis). Individuals who have such deformities are predisposed to thoracic disc degeneration. Thoracic discs may undergo calcification, which can be seen on CT.
MRI is considered the most useful and effective imaging test to confirm the diagnosis of thoracic disc herniation. The thoracic spine is slightly more difficult to image by injecting dye into the spinal canal followed by x-rays. Myelography is may be useful in conjunction with enhanced CT scans to evaluate the bony anatomy and assess calcification of a herniated thoracic disc.
Thoracic disc herniation with or without nerve root compression is usually treated conservatively (nonsurgically). A back brace may be worn to provide support and limit back motion. Injection of local anesthetic around the spinal nerve (spinal nerve blocks) may be effective in relieving radicular pain. As symptoms subside, activity is gradually increased. This may include physical therapy and/or a home exercise program. Preventive and maintenance measures (e.g., exercise, proper body mechanics) should be continued indefinitely. Job modification may be necessary to avoid aggravating activities.
Indications for surgery include myelopathy with loss of bowel and/or bladder control or lower extremity weakness or paralysis. Surgery is also performed for unrelenting radicular pain that is does not improve with an adequate trial of conservative treatment. There are several surgical options. Simple laminectomy is no longer used in the treatment of thoracic disc herniation because of the high risk of neurologic deterioration and paralysis. Excision of the disc may be performed via several different surgical approaches. Fusion of the vertebral joint may be performed if surgery causes lateral instability in the spinal column.
Thoracic disc disease is usually self-limiting and rarely requires surgical intervention. Most cases resolve within 4 to 6 weeks. While conservative treatment is the first line of therapy, outcome varies with the individual, depending upon the severity of symptoms. Results of thoracic disc surgery are not as good as the results of cervical or lumbar disc surgery. Since there is a higher rate of permanent neurologic complications, thoracic disc surgery generally is limited to cases with progressive neurological symptoms or acute disc herniation with myelopathy. A second surgical opinion is strongly recommended.
Individuals who experience a displacement in one of the thoracic intervertebral discs may benefit from a short course of rehabilitation. As stated earlier, the thoracic area is not a common site for displacement of intervertebral disc.
Therapy protocol will focus on decreasing pain and regaining mobility and strength to that particular region of the spine. The therapy program will include instruction in a home exercise program with focus on postural alignment, proper body mechanics and trunk endurance and strength. Modalities such as moist heat or electric stimulation may be used to control pain in order to promote activity and progress with the exercise program.
The exercise program should combine coordination, aerobic conditioning and flexibility exercises. A short course of cognitive pain management may benefit individuals experiencing psychological distress or lack of improvement with treatment. An ergonomic evaluation with modifications may enable the individual to maintain or return to work and reduce the risk of re-injury. Vocational services should be available for individuals who cannot return to their previous job title or do not have a job to which to return.
Progression is rare in younger individuals especially if the symptoms are related to trauma. Rarely, there may be atrophy of muscles innervated by the particular nerve root affected. Disc calcification is another possible complication.