A Twin Study of Chronic Widespread Pain by xuyuzhu


									                            A Twin Study of Chronic Widespread Pain

Niloo Afari, Ph.D.
University of Washington Twin Registry

Chronic widespread pain (CWP) occurs in 4-13% of people and is one of the defining
characteristics of Fibromyalgia (FM). Although tender points were originally considered as
essential to the diagnosis of FM, it is now felt that they reflect pain severity and distress, and
that FM lies at one end of the chronic pain continuum. To truly understand the pathogenesis of
CWP, it would be optimal to study the entire spectrum of individuals who have this symptom.
Another critical issue in the mechanistic study of CWP is what to study. Over the past two
decades, FM researchers have described abnormalities in various components of the central
nervous system as well as high rates of psychological co-morbidities and other chronic
multisymptom illnesses. The role and significance of each of these factors in predisposing to the
illness, directly causing the symptoms, or occurring as a consequence of the condition, are
unclear. The complexity of FM and the continuum of CWP have led us to develop a theoretical
model of CWP that is synergistic and multidimensional. Predisposing factors are of particular
interest in this model since these represent premorbid risk or protective factors that relate to the
development of CWP. Further, predisposing factors can be differentiated from illness-associated
features that occur as a consequence of the condition. A co-twin control study is a powerful
means for examining specific hypotheses about the etiology and consequences of CWP derived
from the theoretical model. Forty MZ and 40 DZ twin pairs discordant for CWP, along with 40
MZ and DZ pain-free control twin pairs will be recruited from the population-based University of
Washington Twin Registry. Twins will undergo an intensive evaluation of the autonomic nervous
system (ANS) function, hypothalamic-pituitary-adrenal (HPA) axis function, exercise capacity,
sleep and activity levels, evoked pain processing, and psychiatric and psychosocial factors
involved in CWP. There are 2 specific Aims: 1) To assess within-pair differences in ANS
function, HPA axis function, exercise capacity, sleep and activity levels, evoked pressure pain
sensitivity, and psychiatric and psychosocial factors between female twins with CWP and their
pain-free co-twins. 2) To assess between-pair effects to determine if the association between
CWP and the above illness characteristics is due to genetics or common environmental factors
by comparing CWP-discordant MZ female twin pairs with CWP-discordant DZ and pain-free MZ
and DZ pairs. Investigating the pattern of differences between twin groups can help to
distinguish factors that are predisposing to CWP and those that occur after the onset of the

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