182 Arthritis and Musculoskeletal Conditions
sensitization process. Furthermore, as the OA disease process
progresses, in”ammation of the af fected joints may trigger
substance P secretion, which in turn should produce more
pain. Thus, although few studies have investigated the role of
the CNS in OA, its role is plausible.
Although an etiological mechanism for the pain of FM is
unknown, CNS involvement is likely. Substance P has also
been suggested to play a role in FM. There is preliminary
evidence for elevated levels of substance P and substance
P agonists in FM patients (Giovengo, Russell, & Larson,
1999; Russell et al., 1994), although not every study found
such effects (Reynolds, Chiu, & Inman, 1988).
Due to the high prevalence of mood disorders and severity
of pain in individuals with FM, some investigators have hy-
pothesized that there may be low levels of serotonin in FM.
Although some researchers have demonstrated an inverse re-
lationship between serotonin levels and pain in individuals
with FM (Russell et al., 1992), others have found no group
differences in platelet serotonin levels between FM, RA, and
low back pain patients (Krag et al., 1995). However, results
of some studies have revealed high levels of antibodies to
serotonin in individuals with FM and depression, suggesting
a possible autoimmune basis for these disorders (Klein &
Berg, 1995; Samborski et al., 1998). Results of these studies
illustrate the need for further research in this area.
Psychological Stress Factors
From the previous discussion it should be clear that the
biological aspects of the stress response are intrinsically
involved in musculoskeletal disease processes. However,
there also exist psychological factors that moderate the
amount of perceived stress experienced. Among these psy-
chological factors are those that affect the appraisal of the
stressor and those that in”uence coping responses.
Appraisal
There are several psychological qualities of stressful
situations that in”uence the degree of perceived stress expe-
rienced. For instance, situations that are perceived as uncon-
trollable, unpredictable, or ambiguous are perceived as more
stressful than situations that are perceived as controllable,
predictable, or unambiguous (Glass & Singer, 1972). These
in”uences on perceived stress have implications for RA, OA,
and FM. First, the chronic pain associated with each of these
conditions coupled with the lack of complete symptom relief
from traditional pharmacological treatment may classify
chronic pain as an uncontrollable stressor. However, while
uncontrollable chronic pain may be common to RA, OA, and
FM, its predictability may vary across disorders. Whereas the
pain of OA is usually exacerbated by activity, the pain of RA
and FM does not necessarily follow a predictable pattern.
This increase in pain unpredictability may affect the degree
of perceived stress experienced by individuals with RA and
FM. Furthermore, the pain of RA, OA, and FM may differ in
terms of ambiguity. For instance, while the pain of RA and
OA stem from identi“able disease processes, the pain of FM
has no known cause. This ambiguity may be a source of in-
creased perceived stress in individuals with FM. Thus, not
only do individuals differ in their appraisal of stressful
events, there may be disease-speci“c ef fects on appraisal as
well. Pain sensations have evolved to allow individuals to
take notice of harm and reduce activity in order to heal. In the
context of RA and OA, which involve identi“able disease
processes, this is an adaptive response. However, in FM,
there is a paradox; pain messages signal that something is
wrong and that the individual should reduce activity, yet the
pain is of benign origin. As a result, individuals with FM
experience a discrepancy between an experience of chronic
pain and the fact that the pain symptoms do not represent an
underlying tissue pathology. This discrepancy may be par-
tially responsible for the •doctor shoppingŽ commonly ex-
hibited in this group, as individuals with FM attempt to “nd a
physician who will acknowledge their experience of pain. It
is also possible that individuals differ in their appraisal of the
discrepancy. Whereas some individuals may experience reas-
surance when told that their pain is of benign origin, others
may interpret this message as either a dismissal of their sub-
jective experience or an oversight of some underlying disease
process. Thus, appraisal factors may interact with pain symp-
toms to produce several of the behaviors observed in individ-
uals with FM.CopingThe adaptiveness of speci“c coping strategies may also be
context- and disease-speci“c (for review, see Manne &
Zautra, 1992). There is evidence that those with RA and OA
who use active coping strategies have more favorable out-
comes than those who use passive coping strategies, which
involve retreat in the face of a stressor. In individuals with
RA and OA, passive coping, but not active coping, is related
to reduced functional status (Af”eck et al., 1992; Zautra
et al., 1995). In addition, coping strategies such as wishful
thinking and catastrophizing account for a signi“cant amount
of variability in physical disability, pain, and depression in
individuals with RA and OA (Beckham, Keefe, Caldwell, &
Roodman, 1991). There is some evidence that individuals
with FM cope differently than those with OA or RA. For