Page 358 Guide to Pain Management in Low-Resource Settings

346 Rolf-Detlef Treede

the spinal cord receives nociceptive input from within In the aura phase, many patients are hypersensitive to
the bone. external stimuli such as light, sound, smell, or touch.
Th is increased sensitivity appears to be related to a de-
Practical consequences fi ciency in habituation. For example, evoked cerebral

Tissue damage restricted to the bone marrow can be potential studies have shown that the normal response
a source of intense nociceptive input. Hence, patients decrement upon repetitive application of visual stimuli
with pain in such conditions do need treatment. How- is absent in migraine suff erers. More recently, such defi -
ever, treatment here does not necessarily have to be by cits have also been shown for pain habituation, by using
analgesics; instead, radiation or chemotherapy may ac- laser-evoked potentials (here an infrared laser applies
tually eliminate the cause of this pain. very brief heat pulses of a few milliseconds’ duration).
Th ere is some evidence that defi cits in pain habituation
Insights on neuropathic pain occur in other chronic pain conditions as well, such as
in cardiac syndrome X.
Th ere has been a long-standing debate on how to de-
fi ne “neuropathic pain.” Th e concept, however, is quite Practical consequences
simple: consider the nociceptive system as the body’s Currently none, but in the future it may be possible to al-
alarm system. Pain is perceived when this system rings leviate chronic pain conditions by treatment modalities
an alarm. As with any other alarm system, there are two that enhance habituation without being directly analgesic.
possible ways the alarm can be activated: (a) it is a true
alarm signaling an actual event; (b) it is a false alarm, Insights on pain in
caused by a defect in the alarm system. Th e usual pain
infants and children
after tissue damage is a case of true alarm by the noci-
ceptive system. In case of neuropathic pain, it is a false Skin innervation occurs at about 7–15 weeks’ gesta-
alarm caused by some kind of damage to the nocicep- tion, and simple refl ex arcs appear as early as 8 weeks.
tive system. Th alamocortical connections are established much later
(from week 20 onwards), and EEG signals and somato-
Practical consequences
sensory evoked potentials start to be present at week
If a patient reports pain in a part of the body that is not 29–30. Th ese electrical brain signals suggest that con-
damaged, consider neuropathic pain as a possibility. To scious perceptions such as pain may be present before
verify this clinical hypothesis, evidence should be sought birth. However, the nervous system is immature at birth
to demonstrate the underlying damage to the nocicep- and undergoes substantial changes postnatally. Immedi-
tive system. Th e patient’s history may reveal a possible ately after birth, cutaneous withdrawal refl exes are lively
etiology such as diabetes, peripheral nerve damage, HIV, and occur with very low threshold, such as mild touch
or previous shingles. Th e sensory examination is of ut- by a pointed object. GABAergic synapses are excitato-
most importance: the distribution of pain and the dis- ry at early developmental stages and become inhibito-
tribution of negative or positive sensory signs should ry only with maturation. After birth, refl exes decrease,
closely match. Sensory testing must include either a whereas cortical stimulus responses increase (detect-
painful test stimulus such as pinprick, or a thermal stim- able by near-infrared spectroscopy, for example). My-
ulus such as contact with a cold object (thermoreceptive elination in peripheral nerves is complete within about
pathways are very similar to nociceptive pathways and 1 year, but it takes 5–8 years in the central nervous
hence are an excellent surrogate). To be able to diagnose system. As soon as a child is able to understand verbal
neuropathic pain correctly, pain specialists need to have instructions, faces pain scales can be used in a similar
some level of neurological training. fashion as visual analogue scales in adults.

Practical consequences
Insights on chronic pain
It is diffi cult to judge the level of pain and discomfort
Migraine is a frequent headache syndrome that has in infants due to their strong refl ex responses that may
a major impact on quality of life. In spite of major re- or may not run parallel to conscious perception. To
search, its pathophysiology is still not fully understood. be on the safe side, adequate anesthesia and analgesia