Thoracic pain

The thoracic region of the spine is relatively inflexible and functions primarily to provide erect posture and assist in weight bearing of the trunk, head, and upper extremities during daily activities. The vertebral bodies are taller posteriorly than anteriorly, resulting in an anterior concavity and normal thoracic kyphosis.

In the thoracic spine, the addition of the sternum, the ribs, and their associated ligamentous structures provide additional support and rigidity. The 10 most superior ribs articulate anteriorly with the sternum and posteriorly with the transverse processes and vertebral bodies. These ribs are oriented vertically, with slight medial angulation in the coronal plane. This arrangement provides the thoracic spine with relatively good stability in the midsagittal plane. However, it also affords less stability in the lateral and rotational planes. Biomechanical studies have shown that thoracic intervertebral discs are most susceptible to injury when torsional and lateral forces are applied in tandem.

Several features of the thoracic spine increase its susceptibility to spinal cord compression associated with thoracic disc herniation, as follows:

• The ratio of the spinal canal to the thoracic spinal cord is smaller than that found in the cervical and lumbar regions. Although the cross-sectional diameter of the thoracic cord is smaller than that of its cervical or lumbar counterparts, the diameter of the spinal canal is proportionally even smaller. Thus, the ratio of the spinal cord to the canal in the thoracic spine is 40%, whereas this ratio in the cervical spine is only 25%.
• The dentate ligaments situated between the spinal cord and the nerve roots restrict posterior movement of the spinal cord within the canal. This makes the thoracic spine prone to vertical compression from anterior disc and bony prominences.
• The natural kyphosis of the thoracic spine places the spinal cord in close proximity to the posterior longitudinal ligament and the posterior aspects of both the vertebral bodies and the discs in the thoracic region. This makes the thoracic cord especially susceptible to ventral compression from herniations.

Normal discs and disc degeneration

The 3 basic structures of normal vertebral discs are the nucleus pulposus, the annulus fibrosus, and the vertebral endplates. The nucleus pulposus is the gelatinous core of the disc and is composed mostly of water and proteoglycans. The annulus fibrosus surrounds the nucleus pulposus and is composed primarily of water and concentric layers of collagen. The vertebral endplates lie on the superior and inferior aspect of the discs adjacent to the vertebral bodies and aid in the diffusion of nutrients into the discs. As a normal part of aging, the water content of the discs decreases, leading to decreased disc height and impaired capability to absorb the axial loads of the spine. Disc herniations, annular tears, and endplate degeneration all can occur.

Location of thoracic disc herniation

Thoracic disc herniation are generally classified into 4 categories. These are central thoracic disc herniations, centrolateral thoracic disc herniations, lateral thoracic disc herniations, and intradural thoracic disc herniations. Central and centrolateral protrusions are the most common and are found in 70% of cases. Intradural herniations are rare and are found in less than 10% of cases. Clinical presentations vary, but the following generalizations are appropriate:

• Central protrusions may cause spinal cord compression, and patients may present with myelopathic symptoms, such as increased muscle tone, hyperreflexia, abnormal gait, and urinary/bowel incontinence.
• Centrolateral protrusions may result in a presentation resembling Brown-Sequard syndrome, with ipsilateral weakness and contralateral pain or sensory disturbances.
• Lateral herniations may cause nerve root compression, and patients may present with a radiculopathy.

Intraosseous disc herniations

Thoracic intervertebral discs can herniate into the spinal canal as well as through vertebral endplates, directly into the adjacent vertebral bodies. The resulting herniations are called Schmorl nodes or cartilaginous nodes. These can occur in association with osteoporosis, tumors, metabolic diseases, congenital weak points in the endplates, or degenerative endplate changes. Although Schmorl nodes often do not cause symptoms, an inflammatory, foreign body–type reaction can occur, resulting in severe pain.

Scheuermann disease, or juvenile kyphosis, is a disorder of childhood in which these types of changes are particularly pronounced. Children with this disorder generally present at age 8-16 years with rigid thoracic kyphoses. Although the exact etiology is not known, endplate degeneration and avascular necrosis of the ring apophysis result in the development of multilevel Schmorl nodes and vertebral wedging. This may cause the patient to have a severe kyphotic posture and pain in the early teenage years.

Annular tears

Tears in the annulus fibrosis may contribute to thoracic discogenic pain (TDP), even in the absence of an associated disc herniation. The outer third of the annulus fibrosis is innervated by the sinuvertebral nerve, which relays sensory information, including pain, to the dorsal root ganglion. Tears in this region, particularly radial tears, may be clinically significant. A study by Schellhas et al evaluated the results of 100 patients with thoracic discographies. ^[5] The study found that greater than 50% of painful discs had annular tears with no evidence of significant herniation.

Calcification

Calcification is also a common finding in thoracic disc herniations, particularly in those discs that are herniated as a result of degeneration. The terms “hard” disc herniations and “soft” disc herniations are used throughout the literature to indicate disc herniations with and without calcification, respectively. The presence and extent of calcification is also important in surgical planning.

 

History

The diagnosis of thoracic discogenic pain syndrome can be challenging. The relative rarity of the condition makes it a diagnosis that is not often considered. Further, the presentation of thoracic discogenic pain syndrome is variable and may resemble that of cervical or lumbar discogenic pain, which is much more common. When considering the diagnosis of thoracic discogenic pain syndrome, pertinent aspects of the patient history include the duration of symptoms, the extent of pain and weakness, and the presence of bowel or bladder symptoms.

Duration of symptoms

Thoracic discogenic pain syndrome most commonly manifests insidiously, with no history of a significant trauma. The initial symptom is usually pain, which then progresses to either radiculopathy or myelopathy to varying degrees. Nannapaneni and Marks described a subset of patients that is young and often presents with a more definite history of trauma. ^[6] These patients tend to have centrolateral disc herniations that either precipitate initial symptoms or intensify existing ones. These patients also tend to present with contralateral pain and sensory disturbances with ipsilateral weakness resembling Brown-Sequard syndrome.

Pain

Pain is the most common symptom in thoracic discogenic pain syndrome and is the presenting symptom in approximately 60% of affected patients. The quality and location of the pain depend on the location of the disc pathology and whether or not neural elements have been compromised. Purely discogenic pain may be dull and localized to the thoracic spine. Although less common, upper thoracic disc herniations may manifest as cervical pain and lower thoracic disc herniations may manifest as lumbar back pain. Pain may also be referred to the retrogastric, retrosternal, or inguinal areas, resulting in misdiagnoses such as cholecystitis, myocardial infarction, hernia, or nephrolithiasis.

 

According to Schellhas et al, annular tears may also have referral patterns based on the anatomic location of the tear. ^[5] Anterior tears may refer pain to anterior extraspinal sites, such as the ribs, chest wall, sternum, or visceral structures. Lateral tears can produce radicular pain to either visceral or musculoskeletal sites. Posterior tears typically produce back pain, in either a local or diffuse pattern.

When a herniated disc compromises thoracic nerve roots, the patient may present with the symptoms listed above as well as radicular pain. This pain may be intermittent or constant and is usually described as electric, burning, or shooting in nature. The distribution is often bandlike, spanning the anterior chest wall. The T10 dermatomal region is most often described as the focus of pain, irrespective of the level involved. When cord compression and myelopathy are present, pain can be in any dermatome distal to the site of compression.

Sensory disturbances

Sensory disturbances may be the presenting symptom in approximately 25% of patients with thoracic discogenic pain syndrome. Numbness is the most commonly reported sensory disturbance, but dysesthesias and paresthesias in a dermatomal distribution may also be reported. The absence of these findings does not exclude thoracic discogenic pain syndrome, but, when present, they are highly suggestive of the diagnosis. A more concerning presentation of sensory disturbances is a wider distribution below the suspected thoracic disc herniation. This is consistent with myelopathy due to cord compression.

Weakness

Weakness may be the presenting symptom in 17% of patients with thoracic discogenic pain syndrome. The motor nerves of the thoracic spinal segments supply the abdominal and intercostal muscles. Although weakness of these muscles may occur, it is unlikely to be an early presenting symptom. Patients are more likely to present with weakness in the lower extremities when compression and myelopathy are present.

Bladder symptoms

Bladder symptoms (eg, incontinence) are the presenting symptom in only 2% of patients. However, bladder symptoms are not uncommon when cord compression and myelopathy have occurred. These patients may also have bowel incontinence.

Physical

Musculoskeletal

The musculoskeletal assessment should include a thorough examination of the cervical, thoracic, and lumbar spine and an evaluation of the abdominal and hip musculature. The findings are nonspecific in the diagnosis of thoracic discogenic pain syndrome, but they may reveal concomitant myofascial pain or patterns of weakness and/or inflexibility that can predispose the patient to thoracic discogenic pain syndrome. These findings are crucial in tailoring conservative treatment to the specific needs of the patient.

 

Sensory

A patient with a thoracic radiculopathy from a herniated thoracic disc may have altered sensation to light touch or pinprick along a dermatomal pattern. However, if a sensory level is established, such that sensation is consistently altered below a specific dermatome, cord compression and myelopathy should be strongly considered. The thoracic dermatomes generally follow a bandlike distribution across the back and chest. Some common landmarks to aid in examination are the nipples for T4, the xiphoid process for T7, and the umbilicus for T10.

 

Motor

Motor examination should include testing of muscle strength and an evaluation of muscle tone. Strength testing of the abdominal muscles is often not part of a routine examination, but it should be performed in the evaluation of thoracic discogenic pain syndrome. Lesions at T9 and T10 can paralyze the lower abdominal muscles but spare the upper abdominal muscles, producing the Beevor sign, which is an upward movement of the umbilicus when the abdominal wall contracts. Having the patient sit upright and then observing for any asymmetric contractions of the rectus abdominus may also be helpful. A pattern of lower extremity weakness associated with spasticity or hyperactive reflexes is a serious finding in patients with thoracic discogenic pain syndrome; it is indicative of myelopathy. Care must be taken to exclude other more common causes of these findings, such as cervical and lumbar myelopathy.

 

Reflexes

A careful examination of the reflexes is critical when determining the degree of upper and lower motor neuron involvement. Hyperactive reflexes signify an upper motor neuron lesion above the level at which the spine is being tested, whereas diminished reflexes indicate a lower motor neuron lesion in the dermatomes being evaluated.

 

Testing of the abdominal reflex can be performed by stimulating the skin overlying the abdominals. The expected response is contraction of the underlying muscles. In male patients, testing of the cremasteric reflex can be performed by stroking the skin on the medial side of the thigh next to the scrotum. The normal response is the scrotum on the side being tested is pulled superiorly.

 

Upper extremity reflexes should be normal unless the patient has concomitant cervical pathology. Patellar and Achilles reflexes are normal in patients with purely discogenic pain or a thoracic radiculopathy. Hyperactive patellar reflexes, Achilles reflexes, or clonus may be seen in persons with cord compression and myelopathy. If decreased patellar or Achilles reflexes are found, lumbosacral pathology should be considered.

 

Provocative maneuvers

Physical examination maneuvers that induce nerve root tension and provoke radicular pain should be performed to help rule out cervical and lumbosacral pathology and to evaluate for thoracic discogenic pain syndrome. The Spurling maneuver, consisting of cervical compression, extension, and ipsilateral rotation, may reproduce symptoms due to cervical radiculopathy. A straight-leg raise test or slump test may reproduce symptoms from a lumbosacral radiculopathy. Neck flexion can provoke symptoms due to thoracic disc protrusions below the midthoracic level.

 

Gait

A number of gait deviations may be observed in patients with thoracic discogenic pain syndrome. These may be due to a pain avoidance strategy or to weakness if myelopathy is present. A common gait deviation in patients with herniated discs is the "sciatic list." Patients often lean away from the herniated disc in order to relieve pressure on the disc and reduce symptoms.

Causes

Up to 90% of herniated discs in the thoracic spine are due to a degenerative process. As a normal part of aging, the water content of discs decreases, leading to decreased disc height and impaired capability to absorb the axial loads of the spine. Disc herniations, annular tears, and endplate degeneration all can occur.

 

Trauma can be an important factor in 10-20% of patients. In patients with symptomatic thoracic disc herniations for which trauma is implicated as the cause, a twisting or torsional movement is often involved. Participation in any sport that involves axial rotation of the spine can potentially increase the risk of disc herniation. These types of forces may be observed in sports such as golf, in which axial rotation of the spine is required at the top of the backswing, with subsequent uncoiling and hyperextension observed through the downswing and follow-through.

 

 

Imaging Studies

Plain radiography

The primary role of radiographs in the evaluation of back pain is to evaluate for fracture, tumors, or infection. However, radiographs can also provide some useful information when evaluating for thoracic disc herniations. Osteophyte formation, disc-space narrowing, and kyphosis are signs of disc degeneration and often occur in conjunction with disc herniation. However, these findings have a low specificity for the diagnosis of thoracic disc herniation. Although not diagnostic, disc calcification is a more reliable finding when evaluating for thoracic disc herniation on radiographs. This finding is present in up to 70% of patients with thoracic disc herniation and is seen in only 4-6% of patients without thoracic disc herniation.

CT myelography

With the advent of MRI, CT myelography is used less frequently in the evaluation of thoracic discogenic pain syndrome. MRI has diagnostic advantages over CT myelography and does not involve injection of contrast into the epidural space. However, CT myelography is good for diagnosing lateral herniations and calcification, and this imaging modality is often used in preoperative planning.

 

MRI

MRI is the most commonly used diagnostic test in the evaluation of thoracic disc herniation. It is the screening test of choice and is extremely sensitive for detecting disc abnormalities. Advantages of MRI compared with CT scanning or CT scanning with myelography include better visualization of the soft-tissue structures, earlier recognition of disc degeneration, and the ability to evaluate in the sagittal plane. See the image below.

Sagittal magnetic resonance image of a lower thoracic herniated disc.

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MRI can be used to determine the size and location of the disc herniation and to characterize it as a protrusion, extrusion, or sequestration. Although helpful in preoperative planning, these features may not be helpful in determining a prognosis. Brown et al retrospectively reviewed the MRI results of 55 patients with symptomatic thoracic disc herniations. ^[7] Fifteen patients ultimately needed surgery and 40 patients did well with conservative management. MRI could not help distinguish the discs in the surgically treated group from the discs in the conservatively treated group. ^[7]

A more useful way of determining the severity of thoracic disc herniation with MRI may be quantifying the amount of neural compression. One such grading system suggested by Kaplan is as follows ^[8] :

• Mild: The anterior epidural fat is not obliterated.
• Moderate: The epidural fat is obliterated, and the thecal sac is displaced.
• Severe: The cord is effaced or the nerve root(s) is displaced.

Despite the usefulness of MRI, it does have limitations. As technology has improved, thoracic disc herniations are more easily recognized. However, all of these thoracic disc herniations may not be clinically significant. Wood et al evaluated 90 individuals without thoracic pain to determine the frequency of abnormalities. ^[9] Intervertebral degenerative changes, annular abnormalities, or both were found in 73% of the subjects; herniation was seen in 37% of the subjects.

MRI is also less sensitive for the evaluation of annular tears, particularly in the thoracic region. The high-intensity zone that commonly represents radial tears in cervical and lumbar MRIs is not seen as often in the thoracic region. These limitations underscore the importance of the patient's history and physical examination. MRI plays an important role in the evaluation of thoracic discogenic pain syndrome, but the results must be interpreted in light of the clinical findings and with knowledge of the limitations of MRI.

 

Other Tests

Electrodiagnosis

Electrodiagnostic studies, including nerve conduction study (NCS), needle electromyography (EMG), and somatosensory evoked potentials (SSEPs), can be useful adjuncts to the history and physical examination. NCS and EMG can be used in the evaluation of thoracic radiculopathy; however, their utility is limited by the limited number of tests, the lack of their ability to localize the level of involvement, and the risk of pneumothorax or penetration of the abdominal cavity with some techniques. However, NCS and EMG can be extremely useful in excluding other possible diagnoses, such as cervical radiculopathy, lumbosacral radiculopathy, and peripheral neuropathy.

 

SSEPs should be considered in cases in which it is unclear whether clinical symptoms are due to an upper motor neuron or lower motor neuron process. SSEPs can help make this distinction and can assist in directing subsequent treatment accordingly.

 

Discography

Thoracic discography may be considered in patients who are considering surgical intervention for predominantly axial back pain that is thought to be discogenic in nature. ^[10] Discograms are most useful when they demonstrate single-level concordant pain that is associated with endplate irregularities or annular tears and normal discs at adjacent levels. However, the results of thoracic discography should be interpreted with caution.

 

Wood et al showed that 55% of discograms performed in patients with symptomatic thoracic pain revealed concordant pain. Whether this large number of positive results represents multilevel disease or a high false-positive rate in the population is unclear. Furthermore, 2 of 10 asymptomatic patients demonstrated pain that could be interpreted as a positive result. Wood et al concluded that long-term prospective studies of surgical outcomes and their correlation with discography results are warranted.