C h a p t e r 3 5
Somatosensory Function, Pain, and Headache
871
Complex Regional Pain Syndrome
The complex regional pain syndrome (CRPS), formerly
known as
reflex sympathetic dystrophy
(RSD), is a rare
disorder of the extremities characterized by autonomic
and vasomotor instability.
36–38
There are two forms of
the CRPS: CRPS I (equivalent of RSD) and CRPS II,
also known as
causalgia.
The International Association
for the Study of Pain (IASP) lists the diagnostic criteria
for CRPS I as the presence of an initiating traumatic
event, continuing pain, allodynia (perception of pain
from a nonpainful stimulus), or hyperalgesia dispro-
portionate to the inciting event with evidence at some
time of edema, changes in skin blood flow, or abnormal
sensorimotor activity in the area of pain. The diagno-
sis is excluded by the existence of any condition that
would otherwise account for the degree of pain and
dysfunction.
39
According to the IASP, CRPS II (i.e., causalgia) is
diagnosed as the presence of continuing pain, allodynia,
or hyperalgesia after a nerve injury, not necessarily lim-
ited to the distribution of the injured nerve, with evi-
dence at some time of edema, changes in skin blood
flow, or abnormal sensorimotor activity in the region
of pain. The diagnosis is excluded by the existence of
any condition that would otherwise account for the
degree of pain and dysfunction. The primary difference
between type I and type II is the identification of a defin-
able nerve injury.
The hallmark of both types of CRPS is pain and
mobility problems more severe than the injury warrants.
Characteristically, the pain is severe and burning with
or without deep aching. Usually, the pain can be elic-
ited with the slightest movement or touch to the affected
area, it increases with repetitive stimulation, and it lasts
even after the stimulation has stopped. The pain can
be exacerbated by emotional upsets or any increased
peripheral sympathetic nerve stimulation. All the varia-
tions of CRPS include sympathetic components. These
are characterized by vascular and trophic (e.g., dystro-
phic or atrophic) changes to the skin, soft tissue, and
bone, and can include rubor or pallor, sweating or dry-
ness, edema (often sharply demarcated), and, with time,
patchy osteoporosis.
The pathophysiologic process of CRPS remains
uncertain. Although abnormalities in sympathetic activ-
ity are observed, recent experimental data suggest that
sensitization of small-diameter, polymodal C and A
δ
fibers to noxious stimuli may be the basis for hyperalgia
to heat and nociceptive stimuli.
38
There is also evidence
that central mechanisms may play a role in sensitization
of central neurons that occurs after intense peripheral
mechanical stimuli or continuous activity in nocicep-
tors. The sympathetic nervous system, either directly or
indirectly through prostaglandin or
α
1
-adrenergic recep-
tor activity, is considered to contribute to the excitation
and sensitization of the nociceptive afferents. Other
proposed mechanisms include neurogenic inflammation
caused by the activation of neuromediators, such as sub-
stance P, calcitonin gene–related peptide, and histamine,
which also mediates inflammation and vasodilation of
microvessels.
36
Recent research demonstrated the pres-
ence of autoantibodies against autonomic nervous sys-
tem structures in patients with CRPS, especially CRPS
II, suggesting that the disorder may result from dys-
function of the autonomic nervous system caused by an
autoimmune attack.
39
Early mobilization after injury or surgery reduces the
likelihood of developing the syndrome.
38
In addition to
addressing the underlying disorder, treatment is directed
at restoration of function. Physical therapy is a corner-
stone of therapy. Pain management involves the use of
standard pharmacologic agents used in the manage-
ment of neuropathic pain, namely, antidepressants (e.g.,
amitriptyline) and antiseizure drugs (e.g., gabapen-
tin). Short-term corticosteroid (prednisone) treatment
may be used in resistant cases. If this does not lead to
improvement, treatment by sympathetic blockade may
be used to provide pain relief and determine the extent
to which the pain is sympathetically maintained. The lat-
ter mechanism, when present, might respond to the use
of a
α
1
-adrenergic receptor antagonist (e.g., terazosin,
phenoxybenzamine). Electrical neurostimulation of the
spinal cord may also be considered. Neurostimulation
not only may provide analgesia, but also may reduce the
burning dysesthesia of which many patients complain.
It may also improve circulation in the affected extremity
by blocking the sympathetic efferent pathways.
38
Phantom Limb Pain
Phantom limb pain, a type of neurologic pain, follows
amputation of a limb or part of a limb.
40
Pain associated
with the loss of a limb can fall into three categories:
phantom limb pain, residual limb pain, and phantom
limb sensations. It is estimated that up to 95% of all
patients who have some form of limb loss will experi-
ence sensations in one of these categories.
40
The pain
often begins as sensations of tingling, heat and cold, or
heaviness, followed by burning, cramping, or shoot-
ing pain. It may disappear spontaneously or persist
for many years and typically occurs within the first
6 months after the limb loss occurs.
40
One of the more
troublesome aspects of phantom limb pain is that the
person may experience painful sensations that were
present before the amputation, such as that of a painful
ulcer or bunion.
Several theories have been proposed as to the causes
of phantom limb pain.
40
One theory is that the end of a
regenerating nerve becomes trapped in the scar tissue of
the amputation site. It is known that when a peripheral
nerve is cut, the scar tissue that forms becomes a bar-
rier to regenerating outgrowth of the axon, which often
becomes trapped, forming a tangled growth (i.e., neu-
roma) of small-diameter axons, including nociceptive
afferents and sympathetic efferents. It has been proposed
that the afferents show increased sensitivity to innocu-
ous mechanical stimuli and to sympathetic activity and
circulating catecholamines. A related theory proposes
that the source of phantom limb pain is in the spinal
cord, suggesting that the pain is due to the spontaneous
firing of spinal cord neurons that have lost their normal
