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Complex regional pain syndromes are prominent in about 4-7% of patients after limb fractures, surgery or injuries.
The results of the study concluded
that SMD, particularly neural under-responsiveness, can act as a potential risk
element for CRPS and therefore screening for SMD is recommended. The study also
allocates the risk index probability clinical tool to
identify those at risk for CRPS immediately after the injury, but the consent
for further research is needed.
Complex regional pain syndromes are
prominent in about 4-7% of patients after limb fractures, surgery or injuries.
It is characterized by voluntary pain regionally related, disproportionate in
its time duration and/or pain intensity after trauma or other lesions. The pain
has a distal predominance of abnormal motor, sensory, sudomotor, vasomotor
edema, and/or trophic characteristics. The evolution of CRPS varies that
usually leads to a severe state of disablement in the affected limb, adversely
affecting the quality of life. CRPS impose a vast individual and cost burden on
society, typically reducing working hours and elevating overall costs. It has a
prevalence rate of about 26.2 per 100,000 individuals in Europe and
approximately 200,000 individuals are diagnosed with CRPS every year in
America.
CRPS is categorised into two types: CRPS
Type 1; identified by a noxious event or a cause of immobilisation with no
recognised nerve injury that and CRPS Type 2; that involves distinct nerve
injury (Type 2). The reason of CRPS is still unclear and various underlying
pathophysiological mechanisms such as genetic and psychological factors;
alterations in somatosensory innervation and sympathetic nervous system
processing; peripheral and central sensitisation; aggravated local and systemic
inflammatory cytokines levels; lower systemic levels of anti-inflammatory
cytokines and catecholamines; and regulating neuroplasticity difficulties have
been indicated. The best way to achieve clinical and optimum outcomes is an
early diagnosis of CRPS and prompt rehabilitation. However, negligence to
examine complicating factors retards the determination, and inappropriate
treatment can lead to CRPS with severe disability.
Various risk factors for the onset of CRPS
have been indicated. It is prominent in females, mostly in postmenopausal
women; individuals who had undergone an ankle injury such as dislocation or an
intraarticular fracture, and a wrist fracture; individuals who are immobilised;
and when the pain level is escalated, higher than usual, in early stages of
post-trauma. Also, a significant association has also been reported between
CRPS and a prior diagnosis of migraine or osteoporosis, but these potential
risk factors were not confirmed across trials. The evidence has also not been
identified for robust genetic associations, and psychological factors such as
anxiety, depression, neuroticism have also not been shown to be predictors for
CRPS development. Recently a higher incidence of posttraumatic stress disorder
(PTSD) in CRPS, compared to the general population and other limb pain
disorders was inferred suggesting that PTSD may also serve as a risk factor for
developing CRPS. The elements for CRPS
onset are still evasive, recognising those at risk for CRPS before surgical interventions,
immediate post-trauma, or very early in the condition, is warranted.
A substantial body of literature about CRPS
suggests the association of the central nervous system regarding sensory as
well as pain processing changes. Especially, impairments in endogenous pain
inhibitory pathways evident and SMD is associated with pain severity, showing
pain hyperalgesia. Moreover, sensory changes occurring in the
contralateral hand were found associated with the ones happening in the
affected hand, indicating central sensory processing alterations as well but
till date, it is not clear whether these alterations are a result of or a
predisposition for developing CRPS.
Sensory modulation dysfunction (SMD), is a
category of sensory processing disorder, that affects single or multiple neural
systems and the capacity to regulate responses to sensory input in an adaptive
manner. It also interferes with work performance, quality of life and
participation in everyday routines. The incidence of the SMD was estimated to
be 5–16% of the population, otherwise healthy. It is characterised by sensory
over-responsiveness (demonstrated as a non-painful stimulus perceived as
unpleasant, aversive, or painful) and sensory under-responsiveness (shown by a
reduced response to stimulus). Sensory over responsiveness was found to be
related to daily pain sensitivity. Sensory over responsiveness in children and
adults has revealed hyperalgesia and prolonged duration of pain lingering sensations, compared to controls,
indicating modulation in endogenous pain in individuals with sensory
over-responsiveness who are otherwise healthy
Rationale behind research:
Identification of risk factors for CRPS onset is
difficult, and to date, no specific clinical symptom has been empirically found
to be a potential risk factor for the emergence of CRPS. Therefore this
cross-study has been conducted to determine the potential risk factors in the
incidence of CRPS.
Objective:
The objective of the cross-sectional study was to
determine the correlation between CRPS and SMD, specifically to elucidate
whether SMD could be considered as a risk factor for CRPS.
Study outcomes:
Time Points: 3 months to 12 years
Outcomes
Baseline: There were
no significant differences observed at baseline
Study outcomes:
The findings of the study suggested that SMD can
be a potential risk factor in explaining the presence of CRPS. Sensory under-responsiveness has a major likelihood in the
occurrence of CRPS than sensory over-responsive or older in age. However, there
were no statistically significant differences achieved in the CRPS severity
between SMD subtypes within patients with CRPS.
Examination of pain perception in daily life
contexts suggests that SMD in healthy individuals co-occurs with regular pain sensitivity.
Individuals with SMD have also explained pain perception alterations in
response to laboratory quantitative sensory testing of pain stimuli. These
alterations include hyperalgesia and pain after-sensation in comparison to
healthy controls, suggestive of compromised endogenous pain modulation [41].
The persistent activation of facilitation increases sensitisation in the dorsal
horn and leads to a state of chronic pain. The co-occurrence of pain
sensitivity (i.e. CRPS) and SMD can be explained by their distinct pain
processing regions in the brain, referred to as the pain matrix. The
interconnected system of brain areas in the pain matrix indicated a significant
BOLD fMRI response to stimuli, either nociceptive or other. Specifically,
non-nociceptive and nociceptive somatosensory stimuli generate indifferent
responses in S1 as well as in some portion of S2, suggesting that
non-nociceptive or nociceptive stimuli are responsible for evoking part of
neural activities determining the BOLD response. These fMRI findings,
therefore, infer that the network of regions, (i.e. the pain matrix) are
involved in nociceptive and non-nociceptive processing.
Age was also accounted as a risk factor, but it
was not a potential factor for the onset of CRPS. Females were thought to have
a higher risk of developing CRPS. However, results were controversial, and
there was a higher incidence of CRPS in postmenopausal women. A study conducted in males determined that
young men are more susceptible to develop CRPS. The present study results were
also consistent with previous studies.
The study results provide a new way for
clinicians to determine a potential risk that may contribute to the early
diagnosis of CRPS. Also, evaluation of pain by experienced clinicians might
accelerate the diagnosis process, and referral to pain management specialists
and a multidisciplinary team relates to better outcomes
PLoS ONE 13(8): e0201354.
Sensory modulation dysfunction is associated with Complex Regional Pain Syndrome
Bar-Shalita et al.
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