Pain

• Author: Samuel D. Hodge, Jr./Jack E. Hubbard
• Profession: Skilled litigator, is chair of the department of legal studies at Temple University/Professor of Neurology at the University of Minnesota
• Pages: 347-406

Pain

The secret of success

is learning how to

use pain and pleasure

instead of having pain

and pleasure use you.

If you do that, you’re

in control of your

life. If you don’t,

life controls you.

Tony Robbins

(1960– )

6

Overview

Spine pain affects over 80 percent of the population at some point during their lives and

can take many forms, from discomfort in the lumbar region to the mid-back to the neck.

Pain from the spine can even radiate to an extremity and be associated with weakness

or a pins-and-needles sensation. Common reasons for this discomfort include muscular

and nerve issues, arthritis, and degenerative disc and joint disease.1 Pain originating from

the spine is also not limited to middle-aged people and may occur at almost any interval

during the life cycle. Research reveals that children are susceptible, workers are at risk,

and active individuals between the ages of 35 and 55 are particularly in jeopardy. The

elderly have a much higher danger for falling, which can result in debilitating fractures

of the neck or compression fractures in the thoracic area. Studies also demonstrate that

genetics may influence disc degeneration, which often causes pain.2 These feelings of

discomfort, however, are not limited to the back and can occur in any area of the body.

Pain can be acute or chronic and often has a psychological component.

Statistically, pain is the number one reason for going to a doctor’s office, accounting

for about 80 percent of all visits.3 In fact, most medical conditions are associated with

some type of discomfort. A survey of adults within the United States reveals that almost

31 percent of individuals reported chronic pain lasting more than six months, with a

greater prevalence in women (34 percent) than men (27 percent).4 The economic impact

of pain is also staggering. One estimate for the yearly cost of chronic pain is $86.2 billion

a year.5 Another study reported that 13 percent of the work force was impaired because

of pain for a given two-week period, leading to an estimated cost of $61.3 billion.6 Pain

is also the foundation for monetary awards in most workers’ compensation and personal

injury cases. Despite the ubiquity of this problem, most physicians and lawyers have only

a rudimentary understanding of this obnoxious sensation. This chapter will discuss pain

by considering its definition, neurobiology, acute versus chronic forms, the concepts of

psychological influences and how they differ from malingering, and a number of specific

chronic painful conditions and syndromes.

Definitions

Pain is difficult to define, but we know it when we feel it. In an objective, clinical definition,

the International Association for the Study of Pain (IASP) defined the term as “an unpleas-

ant sensory and emotional experience associated with actual or potential tissue damage,

or described in terms of such damage.”7 However, this definition did not encompass the

behavioral and psychological aspects of pain. This was addressed in 1994, when the IASP

added definitional amendments that recognized the impact of psychological factors, and

the fact that actual tissue damage may not have to occur in order to trigger discomfort.8

348 ◆ CHAPTER 6

A multidimensional problem, pain is seemingly simple but, at the same time, enor-

mously complex. The severity of pain, from a simple paper cut to chronic debilitating low

back pain, depends upon a balance between the organic cause of the discomfort and the

psychological status of the person.

To set the stage for this discussion, it is helpful to further categorize pain into acute,

chronic, and cancer forms. Acute pain is caused by immediate tissue damage resulting from

an injury, such as from a bone fracture or kidney stone. This pain is self-limited and serves

a useful, protective role. When a person stubs a toe, there is significant discomfort; the foot

is then rested, and the pain eventually recedes. If one’s hand gets too close to a fire, it hurts,

and the person quickly pulls it back, with pain serving a protective function. On the other

hand, chronic pain (of noncancerous origin) is long lasting, usually more than three months.

Extending past the time of normal healing, chronic pain serves no biological purpose, has

no protective function, and is often associated with suffering, depression, and disability.

This form of pain is not just acute discomfort that lasts longer, but is a disease in of its

own. The American Academy of Pain Medicine has proposed the term maldynia (Greek

for “bad pain”) to describe this maladaptive discomfort because it can occur in the absence

of ongoing noxious stimulation and does not promote healing and repair.9 Cancer pain has

components of both acute pain, in that the cancer may be causing ongoing tissue destruc-

tion, and chronic pain, as it is of long duration with associated suffering and disability.

No single medical or surgical specialty claims pain as its own because this problem

crosses many specialty lines. Those physicians who typically have a practice in pain medi-

cine include anesthesiologists, physiatrists, and neurologists.

Neurobiology of Pain

Acute Pain

The pain pathway transmitting painful information directly from an injury or diseased area

to the brain is a three-neuron circuit, consisting of first-, second-, and third-order neurons.

Figure 6-1. Pain receptors in the skin and tissues of the body, termed nociceptors, are free

nerve endings of sensory nerves. Stimulation of the nociceptors generates an impulse

carried by the sensory fibers in the peripheral nerves, termed the first-order neurons, toward

the central nervous system (see chapter 5). The cell bodies for these neurons are found in

the dorsal root ganglia along the spinal cord and the trigeminal ganglion in the head. More

specifically, only specific afferent (sensory) fibers that are thinly myelinated (A-delta) or

unmyelinated (C fibers) transmit pain information. Figure 6-2.

In addition to these pain fibers, peripheral nerves contain larger diameter myelinated

fibers (A-beta) that carry the sensations of touch, pressure and position (proprioception)

senses. In the gate control theory of pain proposed in the 1960s by Melzack and Wall,

these larger diameter fibers are suggested to close neural “gates” within the spinal cord

by stimulating inhibitory neurons that block the incoming pain-producing A-delta and

C-fiber input. Figure 6-3. The gate control theory explains why rubbing an injured

area seems to help reduce the pain and is the basis of the use of TENS (transcutaneous

electrical nerve stimulator) units.

Transmitting pain information from the head, the trigeminal nerve (cranial nerve V) is the

first-order neuron that sends pain signals from a pain-generating condition, such as from a

toothache or broken nose, toward the brain stem. Figure 6-4. In the rest of the body, however,

the spinal nerves transmit this information toward the spinal cord. Figure 6-5. Within the

spinal cord, the dorsal nerve root makes synaptic connection in the dorsal horn with the

second-order neuron in this pathway. Figure 6-1. The second-order neuron for sensation from

the head (trigeminal system) is located within the trigeminal nucleus in the brain stem.

Second-order neurons from the dorsal horn form the spinothalamic tracts, which cross

over to the opposite side and run up through the brain stem to the thalamus within the

brain. Figure 6-1. Because of this spinothalamic tract crossover, injury on one side of the

brain or spinal cord results in sensory symptoms/loss on the opposite side of the body.

Within the thalamus, the second-order neurons synapse on the third-order neurons,

which, in turn, project up to the higher centers of the brain, especially the cerebral cortex,

PAIN ◆ 349

FIGURE 6-2.

Sensory  ber types.

Sensory information from the

skin is carried in by two types of

nerve fibers—those that transmit

pain (C fibers) and those that

transmit nonpainful sensation

(A-delta fibers) such as touch. In

comparison, C fibers are smaller

in diameter, thinly myelinated and

more slowly conducting that the

A-delta fibers.

FIGURE 6-1.

The pain pathway.

Acute pain is experienced via a

three-neuron pathway. Starting

at the pain receptors, the first-

order neuron transmits nocicep-

tive (painful) information from

the skin to the dorsal horn of the

spinal cord with its cell body in

the dorsal root ganglion. The

second-order neuron transmits this

information from the dorsal horn

up the spinal cord through the

brain stem to the thalamus in

the brain. The third-order neuron

transmits painful information

from the thalamus to the sensory

cerebral cortex of the brain.