NEUROLOGY
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HOW C NTRALiZ D PAiN D V LOPS
f a peripheral painful injury doesn’t heal, inflammatory
mediators and possibly electronic signals from the injury site
enter the spinal cord and CNS4-11 (Figure 1).
Microglial cells activate and produce neuroinflammation.5-7,9
Neuron hyperexcitability known as central sensitization occurs.10 Glutamate and other excitatory amino acids are released in
the inflammatory process, causing tissue destruction in the CNS. In
this process, memory of the pain somehow becomes permanently im-
Figure
How Centralized Pain Develops
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CHEMICAL AND/OR ELECTRONIC
SIGNALS ENTER CNS
MICROGLIAL CELL ACTIVATION
NEUROINFLAMMATION
RELEASE OF EXCESS GLUTAMATE/
NEUROTOXINS
CELL DEATH, APOPTOSIS, REFORMATION
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There are 3 basic time frames or patterns whereby centralized
pain develops after nerve injury:
1. 6
to 8 Weeks Postinjury
The classic situation is surgery.14 It has long been
observed that if postoperative pain continues for
about 6 to 8 weeks, it becomes persistent. The same applies
to traumatic injuries.
2. Progressive
INJURED PERIPHERAL NERVES
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TiM FROM INJURY TO ONS T OF
C NTRALiZ D PAiN
Transition From Peripheral Pain
Some patients have intermittent peripheral pain that
slowly transforms into centralized pain. The process may take months
or years. It may be precipitated by some event, such as trauma
or infection. Patients will give a history that they were doing well
until they rather suddenly developed constant, daily pain.
Their description may be instructive. For example, they will say things like,
“I was doing OK until suddenly the pain took me over,”
or “I just got worse over time until one day I couldn’t
get out of bed.”
3. Instant
Development
Some patients have a sudden, unexpected, severe injury such as
a gunshot or fall, and permanent pain begins almost at the instant
the injury occurs. Patients may report the onset of severe,
constant pain at the time of injury that subsequently never varies
over time despite many therapies and interventions
including surgery.
COMPLiCATiONS
There are 3 major basic complications from centralized pain:
IMPRINTING OF PAIN SENSATION
1. Immobility
Fatigue, depression, physical impairments, and inability to carry out
activities of daily living may occur.
printed.1,4,11 The inflamed, hyperexcited tissue in the CNS causes excess efferent electronic signals manifested by allodynia.12,13 Centralized pain, with its underlying neuroinflammation and hyperexcitable
cells, displays a characteristic clinical profile that can be recognized
and diagnosed. As with other diseases, centralized pain can be mild,
moderate, or severe.
12 | PWJ | www.painweek.org
2. Hormonal
A most serious complication is osteoporosis, which can lead to
spinal collapse. It is due to excess pituitary–adrenal overstimulation and
elevated cortisol serum levels. Muscle wasting and a catabolic state
due to deficiencies of testosterone and other hormones can occur.
Q3 | 2013