Visceral versus musculoskeletal pain

Because referred pain from visceral problems can mimic pain of musculoskeletal origin and vice versa, the first step towards diagnosis must always be to differentiate these two categories. The character of the pain is usually of little help in the differential diagnosis because it has the same features in both. Pain referred from heart, lungs and intestines is usually poorly localized and vaguely delineated, and is referred to a segmental or multisegmental distribution. The behaviour of the pain may also mislead the examiner. One of the main characteristics of pain in lesions of moving parts is that it is brought on by posture and movement. This is also the case in thoracic lesions: if the patient’s symptoms depend on activity rather than on visceral function, a cause originating from moving parts should be considered. However, it is important to keep in mind the fact that posture, physical activity, a deep breath or a cough may also influence visceral pain in the thorax or abdomen.

The best method of differentiating is to work in two complementary ways: exclusion of any visceral disorder through a thorough internal check-up, together with positive confirmation of a provisional orthopaedic diagnosis (Fig. 25.1). This routine will also safeguard against unnecessary technical investigations and delays in diagnosis and treatment.1–3

Discal lesions

Discodural and discoradicular interactions are well-known causes of cervical and lumbar pain.

In a discodural lesion, a shifted component of the disc impinges on the dura and causes pain that has multisegmental characteristics (crossing the midline and occupying several dermatomes). Discodural conflicts are characterized by two sets of symptoms and signs: articular and dural (see Ch. 33).

In a discoradicular lesion, the subluxated disc component impinges on the nerve root and its dural sleeve. The pain and paraesthesia that result are strictly segmental. Discoradicular conflicts are characterized by three sets of symptoms and signs: articular, root and cord.

Disc lesions also commonly occur in the thoracic spine but often show characteristics that are quite different from those found at the lumbar and cervical spines.

Non-discal lesions

In the thorax, non-discal musculoskeletal lesions are also encountered frequently. To name but a few: ribs, rib joints, cartilage, intercostal and abdominal muscles. This is in contrast to the cervical and lumbar spines, where lesions of the disc are the principal cause of dysfunction and pain.

Dura mater and nerve roots

Pain originating from the dura mater is referred in a multisegmental way: it crosses the midline and may cover several consecutive dermatomes (see p. 18). A possible explanation for this phenomenon may lie in its multisegmental origin, which is reflected in the considerable overlap between the fibres of the consecutive sinuvertebral nerves innervating its anterior aspect.⁴ Recent research has demonstrated that dural pain may spread over eight segments with considerable overlap between adjacent and contralateral dura mater.⁵ This may be an explanation for the fact that lower cervical discodural conflicts may produce pain that spreads into the upper thoracic level (Fig. 25.2a) or that lumbar dural pain causes pain in the lower thoracic region (Fig. 25.2b).

Pain originating from a nerve root sleeve has a strict segmental reference and is restricted to the borders of the dermatome.

Thoracic disc lesions may thus cause referred pain in the thorax, not only as the result of extrasegmental reference in the case of discodural contact, but also when a discoradicular interaction has been created. However, cervical and lumbar discal lesions may also be the origin of thoracic referred pain.

Nerves

Bones

Osseous structures usually do not give rise to much in the way of referred pain; the pain remains typically local. Intense though localized pain is a warning sign and the following conditions should be considered:

Joints and ligaments

Ligaments and joints consistently obey the rules of referred pain, which means that the deeper the location of the affected structure and the closer its position to the midline, the more referred pain is to be expected. On the other hand, the further the lesion lies from the spinal axis and the more superficial it is, the more accurate will be its localization by the pain it provokes.

Muscular lesions

Muscular sprains of the intercostal muscles, the abdominals and the muscles of the shoulder girdle usually provoke well-localized pain at the site of the lesion.

The heart

Pain arising from disorders of the heart can be referred to dermatomes C8–T4 because the heart is derived largely from these segments. Therefore pain can radiate towards the tip of the shoulder, to the anterior chest and to the corresponding region of the back. It may also be referred towards the ulnar side of both upper limbs, though referral to the left side is more common (Fig. 25.4a). Pain from the pericardium always arises from the parietal surface because this is the only part which has a sensory innervation.

The aorta

Pain from the aorta, as in dissecting aneurysm, may be felt behind the sternum or in the abdomen, depending on the exact level of the disorder. It often radiates into the back and may expand as the lesion progresses.

The lungs

The lungs are insensitive. Therefore pain is caused either by the parietal pleura, as in pleurisy, or by invasion of the chest wall by a tumour.

The oesophagus

Disorders of the oesophagus (T4–T6) usually give rise to pain felt at any part of the sternum, often radiating between the scapulae into the back (Fig. 25.4b).

The diaphragm

The central part of the diaphragm is mainly derived from the third, fourth and sometimes, although rarely, the fifth cervical segments. Pain from irritation of the central part of the diaphragm is felt at the tip of the shoulders and the base of the neck. Pain from the peripheral part is felt more locally in the lower thorax and in the upper abdomen at the costal margin (Fig. 25.4c).

The stomach and duodenum

Pain from stomach and duodenum (T6–T10) is most commonly felt in the epigastrium and upper abdomen, sometimes substernally and exceptionally in the lower thoracic part of the back (Fig. 25.4d).

The liver, gallbladder and bile ducts

The liver is derived from the right side of T7–T9. The gallbladder and bile ducts are of right T6–T10 origin. Pain is felt in the right hypochondrium and may radiate towards the inferior angle of the right scapula (T7–T9) (Fig. 25.4e).

The pancreas

Patients suffering from a pancreatic disorder complain of upper abdominal pain often referred to the back at T8 (Fig. 25.4f).

The spleen

Pain arising from disorders of the spleen is usually felt in the left hypochondrium, sometimes in the left side at low thoracic level (T7–T10).

The small intestine, appendix and colon

Problems in the small intestine (T9–T10) give rise to pain felt around the umbilicus. In disorders of the colon (T10–S5), pain is usually felt in the neighbourhood of the lesion. The appendix is a T10–L1 structure.

The kidneys and ureters

Disorders of kidney and ureters (T10–L1) give rise to pain felt posteriorly in the side, at and just below the lower ribs, and at the anterolateral aspect of the abdomen. The pain often radiates towards the testicles or the labia (Fig. 25.4g).⁷

Reproductive system

Disorders of the ovaries (T11–L1) may result in unilateral low abdominal pain, sometimes felt in the periumbilical area. Testicular problems (T11–L1) give rise to scrotal pain, sometimes radiating into the groin and to the side.

See Box 25.1 for a summary of referred pain in the thorax and abdomen.