Disorders of the thoracic spine: Disc lesions

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27

Disorders of the thoracic spine

Disc lesions

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Although the spine is anatomically part of the thoracic cage, we prefer to discuss the thoracic disorders in two main categories – spinal lesions (this chapter and Ch. 28) and lesions of the thoracic cage and abdomen (see online chapter Disorders of the thoracic cage and abdomen). Thoracic ankylosing spondylitis is discussed separately (Ch. 29). This is done to standardize the discussion of the spine throughout, in the hope that a better clinical understanding may result.

Introduction

Cervical and lumbar disc lesions are widely accepted as common causes of pain. For the thoracic spine, the situation is different. Although thoracic disc lesions giving rise to compression of the spinal cord are well recognized,1–5 disc protrusion resulting in pain without causing neurological signs is poorly documented.6 The incidence of thoracic disc lesions affecting the spinal cord is about one case per million people per year,3,7 usually affecting adults, although cases have been reported in children as young as 12.8 The existence of minor thoracic disc lesions provoking pain in the absence of cord compression was first established by Hochman, who removed a disc protrusion at T8–T9 in a 67-year-old lady with continuous unilateral pain in the thorax.9 Neurological signs were not present. The diagnosis was established by computed tomography (CT).

The incidence of minor thoracic disc lesions is much higher. Degenerative changes of the thoracic spine are observed in approximately half of asymptomatic subjects and 30% have a posterior disc protrusion.10 A recent magnetic resonance imaging (MRI) study found a prevalence of thoracic disc herniations of 37% in asymptomatic subjects, disc bulging in 53% and annular tears in 58%.11 Another study of asymptomatic patients identified impressive disc protrusions in no less than 16%.12 An unexpectedly high prevalence of thoracic disc herniation (14.5%) was also demonstrated in the thoracic spines of a group of 48 oncology patients examined by MRI.13 Although these relatively high figures do not correspond to the real clinical situation, we believe that symptomatic thoracic disc protrusions are far more common than is generally accepted and agree with Krämer,14 who estimated the frequency of thoracic disc lesions to be about 2% of all symptomatic disc lesions. Recent studies also confirmed the incidence of symptomatic thoracic disc prolapses as being between 0.15% and 4% of all intervertebral disc prolapses.15,16

However, the clinical diagnosis is often not made and the patients are frequently classified as suffering from intercostal neuralgia, neuritis, cardiac neurosis or pleurodynia. If left untreated, the pain can persist for many years, causing continuing morbidity. Nevertheless, the majority of such lesions can easily be reduced in a few manipulative sessions, fully relieving the patient’s pain.

Although more frequently present than commonly believed, thoracic disc protrusions are clinically far less common than those in the lumbar spine because of the greater rigidity of the thoracic spine. This is partly a result of the stabilizing effect of the rib cage on the thoracic spine and partly due to the thoracic intervertebral discs, which are thinner on account of a less voluminous nucleus pulposus.17 Therefore extension and flexion movements are of a smaller range in the thoracic spine.

Minor thoracic disc lesions occur most often between T4 and T8. Those with cord compression are usually found in the lower half of the thorax.6,18 About 70% lie between T9 and T12, the commonest level (29%) being T11. A logical explanation for this could be that the lower segments have an increased mobility due to free ribs at these levels.19 Another reason could be that the cord has a critical vascular supply at this level.20

Clinical presentation

It is hypothesized that disc degenerations and disc displacements are of themselves painless events because the disc is almost completely without nociceptive structures. Clinical syndromes originate only when a subluxated fragment of disc tissue impinges on the sensitive dura mater or on the dural nerve root sleeve. This clinical hypothesis is extensively discussed in the lumbar section of this book (see Chs 31 and 33).

Disc displacements (protrusions and prolapses) are either soft (nuclear) or hard (annular), and may have a posterocentral or posterolateral localization.

Posterocentral protrusions compressing the dura mater may provoke multisegmental pain, which is mainly referred into the posterior thorax but may also spread into the anterior chest, the abdomen or the lumbar area.21 The pain is never referred down the arm. When a posterocentral displacement increases, cord compression can result.

Posterolateral protrusions interfering with the dural sleeve around the nerve root result in pain that is segmentally referred into the corresponding dermatome. A more massive posterolateral protrusion may compress the ganglion or the nerve root fibres, resulting in motor and/or sensory disturbances in the innervation area of the root.

When the T1 nerve root is compressed by a disc lesion, pain is referred to the inner side of the arm between elbow and wrist. A T2 nerve root impingement creates pain referred towards the clavicle and to the scapular spine and down the inner side of the upper arm. The corresponding dermatomes of the T3–T8 nerve roots follow the intercostal spaces, ending at the lower margin of the thoracic cage. The dermatomes of T9–T11 include a part of the abdomen, and T11 also includes part of the groin (see Fig. 25.3).22,23

Thoracic disc protrusions may give rise to four different clinical presentations: chronic thoracic backache, acute thoracic lumbago, thoracic root pain and spinal cord compression (Cyriax:24 pp. 202–205).

Each clinical pattern corresponds to a specific type of disc lesion. Besides dural and articular signs and symptoms, elements which may indicate compression of the spinal cord must always be sought.

Symptoms and signs

The clinical findings in symptomatic thoracic disc displacements are analogous to the lumbar and cervical disc syndromes. Again, both dural and articular signs and symptoms can be identified (see Ch. 52).

Articular signs

A disc lesion usually affects only a part of the intervertebral joint. Therefore, certain movements cause biomechanical changes that result in forcing the protrusion against the dura. Consequently, it is to be expected that on clinical examination only some of the active movements will increase the discodural interactions while other movements will be without effect and therefore painless. This results in a partial articular pattern, which is an absolute condition for the diagnosis of a disc protrusion, although it is not pathognomonic.

Examples of non-articular patterns are illustrated in Figure 27.1.

Depending on the degree of the compression, the partial articular pattern is more or less pronounced: more tests are painful and more severe pain is present. However, frequently, only one movement is painful, most commonly one of the rotations.

Often both articular and dural signs are present, although the latter are sometimes absent.

Exceptionally, a combination of a partial articular pattern with pain on one or more resisted movements is found. In this event, the question that arises is whether there is a muscular problem or a lesion of an inert structure. In the latter, pain on passive movements is more severe whereas, in the former, resisted movements are more painful.

Pain and limitation on side flexion towards the painless side as the only positive movement does not match the pattern of a disc lesion. Other disorders, such as a pulmonary or abdominal tumour with invasion of the thoracoabdominal wall, must be considered. An intraspinal tumour – for example, a neurofibroma – is also possible (see online chapter Disorders of the thoracic spine and their treatment).

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If pain and limitation on side flexion away from the painful side is the only abnormal movement (Fig. 27.2), a tumour should be suspected.

Clinical types of thoracic disc protrusion

Symptomatic disc displacements in the thoracic spine may give rise to four different clinical syndromes: acute thoracic ‘lumbago’, chronic thoracic backache or ‘dorsalgia’, thoracic root pain and spinal cord compression (Figs 27.3–27.5).24 Each syndrome corresponds to a specific type of disc lesion.

It is obvious that, besides dural and articular signs and symptoms, elements that may indicate compression of the spinal cord must always be sought.

Thoracic backache

A small annular posterocentral disc displacement causes a unilateral discodural interaction. The subsequent unilateral interscapular pain is of moderate severity and is usually brought on by prolonged activities or postures in anteflexion. The pain gets worse during or after particular movements or positions and wears off on rest, but seldom disappears completely. In chronic thoracic backache there is no spontaneous recovery and untreated pain can persist for many years.

Because the pain is usually not severe, the articular signs are not always very impressive. However, no matter how subtle the outcome of the tests, some ‘asymmetry’ in the clinical picture will always be present. It is, for instance, not unexceptional to find only one articular movement that is slightly positive, very often one of the rotations.

This non-articular pattern, in the absence of pain on resisted movements, can usually be interpreted as the outcome of a disc lesion. A further argument in favour of this diagnosis is when neck flexion increases the pain on full passive rotation of the trunk (dural sign).

If both posterior pain and anterior thoracic pain are present, the posterior pain is often influenced by articular movements and the anterior pain is increased by neck flexion.

Disc lesions at level T1 and T2 may give rise to diagnostic difficulties in that very little spinal mobility exists at this level and articular movements may have no influence at all on the pain, so none is positive. The pain is often provoked only by flexion of the neck, which then suggests a cervical disc lesion. When this pattern is found, a differential diagnosis between both types of disc protrusion must be made. Stretching the T1 root and performing all three scapular movements provides the key: they may provoke or increase the pain in a high thoracic disc lesion but usually have no influence on a cervical disc protrusion.

In chronic thoracic backache there is no spontaneous recovery and untreated pain can persist for many years.

All cases of thoracic backache from a disc protrusion, in the absence of any contraindication, should be treated by manipulations, which are usually quickly successful. If this fails, traction must be tried. If there is frequent recurrence, sclerosant infiltrations into the different ligaments and facet capsules must be given to increase spinal stability.

Special case: self-reducing disc lesion

As the term implies, the disc undergoes spontaneous reduction. Patients who suffer from this condition usually sit for most of the day. On waking up in the morning they are symptom-free but, after they sit for some hours, pain starts in the mid-thorax and gets progressively worse. On lying down, the pain gradually eases off. The time needed for the pain to disappear fully depends on the degree of displacement and is initially from 10 to 15 minutes. Later, or if the patient sits for a longer period, it may take an hour or more. Pain may be absent when prolonged sitting is not part of the daily routine – for example, at weekends.

In this condition the disc gradually dehydrates as the result of the prolonged sitting position.25 Simultaneously, the imposed kyphosis pushes the whole intra-articular content of the disc posteriorly, compressing the dura mater and resulting in thoracic backache. On lying down, the effects of hyperkyphosis and gravity are largely diminished and the disc shifts spontaneously back into its original position. These patients should avoid prolonged anteflexion. Manipulative reduction is useless but sclerosant infiltrations may be helpful.

Acute thoracic lumbago

Due to a combined flexion–rotation movement of the trunk, the patient becomes suddenly immobilized by a sharp posterior pain in the thorax, with the trunk fixed in flexion. The condition is similar to acute lumbago at the lumbar spine. In both, the underlying cause is a posterocentral disc protrusion. Pain is usually felt posteriorly in the centre of the back, radiating unilaterally or bilaterally around the chest. In high thoracic lesions, the pain may even reach the sternum; in low thoracic lesions, the pain is sometimes referred to the abdomen.

A deep breath is very painful and normally hurts more than a cough. Sudden onset in the absence of injury in a middle-aged person, together with pain on deep inspiration and on neck flexion, is very suggestive of such a disc lesion.

A partial articular pattern is present in which three, four or five movements are painful, and in severe instances all movements cause pain, but still in an asymmetrical way. The symptoms and signs are thus much more pronounced than in thoracic backache.

If the patient stays in bed for some days, spontaneous resolution occurs over about 2 weeks. Cure can be obtained much more quickly by manipulative reduction. Exceptionally the pain can be so severe that the patient can hardly stand up or needs a great deal of time to turn around on the couch. Such patients should remain in bed until they have improved to such a point that normal manipulations become possible. A manipulative attempt should not be made during the initial period because it is unbearable. Sometimes special oscillatory techniques can be tried.

Recurrence may occur but the pain is not necessarily always felt at the same side.

Thoracic root pain

As in the cervical and lumbar spines, two types of root pain can be encountered: a primary and a secondary posterolateral protrusion. The latter is more common. In the first type, the protrusion is deviated in a posterolateral direction from the onset; in the second, there is first a posterocentral protrusion that later shifts laterally, analogous to a lumbar disc lesion.

Both types of root compression give rise to segmental referred pain. This has a unilateral band-shaped distribution that follows the intercostal nerves. At the thoracic level a posterolateral protrusion seldom gives rise to pins and needles. If present, they follow the same segmental distribution as the pain. As the T12 dermatome spreads into the lower abdomen, interference with this nerve root can result in pain and occasionally pins and needles in the groin and/or the testicles.26

On functional examination, a partial articular pattern is usually found. Occasionally, the patient feels nothing on articular movements but flexion of the neck provokes a sharp unilateral sternal pain, sometimes accompanied by pins and needles in the same place. As flexion of the neck also stretches the nerve roots via the dura, one of these can be pulled further against a protrusion, resulting in a sudden pain.

Neurological signs are seldom encountered and, if present, are always difficult to diagnose. As the majority of the thoracic nerve roots cannot be stretched by movements of arms or trunk, an analogue of straight leg raising does not exist. Moreover, motor deficit, except for a T1 lesion, cannot be tested. The only feature that is occasionally found is numbness. When present, it is of little help in determining the exact level of the protrusion because the dermatomes overlap. Only numbness in the groin draws attention to a nerve root palsy – T12. In rare instances, an area of hyperaesthesia is felt in the front of the chest.

A T1 root palsy is detected during the clinical examination of the cervical spine. It is seldom the result of a disc protrusion but usually the outcome of a serious disorder such as a superior sulcus tumour of the lung, a neurofibroma or vertebral metastases. Although T1–T2 discoradicular compressions with neurological deficit have been reported,27–29 it should be kept in mind that if a neurological deficit of T1 is present, more severe disorders should always be excluded first (see see online chapter Disorders of the thoracic spine and their treatment).

Thoracic disc lesions compressing a nerve root do not usually resolve spontaneously, although there are a few reports of spontaneous regression at a lower thoracic level.30,31 However, posterolateral thoracic disc protrusions which cause root pain remain reducible by manipulation, no matter how long they have existed. Where manipulation has failed or where neurological deficit is present, a sinuvertebral block should be given.

Compression of the spinal cord

The spinal cord is most vulnerable at the lower thoracic levels, between T9 and T12,29,32 because the spinal canal is at its narrowest there and the vascularization is at its most critical.33 It has been suggested that signs of cord compression do not always stem from pressure on the cord itself, but rather are the result of interference with the blood supply.3–5

Osteophytes narrowing the spinal canal are an extra contributing factor.34 Previous injury to the thoracic spine can also play a role in the later development of cord compression, although this circumstance is rare.

History

The most commonly observed chronological sequence in cord compression is pain, followed by sensory disturbance, motor weakness and finally visceral dysfunction. All of these features may be present in any combination.

Pain

Initially almost all patients complain of pain. It is never particularly severe, often has a vague band-shaped distribution, and may sometimes disappear completely.35–38 It is usually localized in the back, although it may radiate into the pelvis or groin and down the legs. Occasionally, patients complain of subumbilical pain.1 The quality varies from a constant, dull and burning pain to – exceptionally – a lancinating, cramping and spasmodic pain.

Functional examination

The functional examination normally confirms what is already expected from the history. The most characteristic signs are found on neurological examination; the articular signs are of secondary importance.

Some or all of the following neurological signs may be present:

• Disturbed coordination with spastic gait.

• Increased muscle tone, with the affected muscles not limited to one myotome.39 Occasionally, weakness of the lower abdominal muscles can be demonstrated, when the umbilicus is seen to move as the patient attempts to sit up.1 This is known as Beevor’s sign.

• Weakness and/or atrophy of some lower limb muscles.

• Hyperreactive patellar or Achilles tendon reflexes with ankle clonus.

• Occasionally, absent tendon reflexes, particularly and inevitably when a flaccid type of paraplegia is present. The abdominal reflexes are often absent or diminished, most commonly in both lower quadrants. All these signs may be unilateral or bilateral.

• Positive Babinski’s and Oppenheim’s signs.

• Absence of the cremasteric reflex.

• Numbness.

• Limitation of straight leg raising, sometimes bilateral.2

• Occasionally, a Brown–Séquard syndrome in cord compression.6

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