Objective
We sought to assess the concurrent validity and interrater reliability of the cotton-tipped applicator (CTA) test as a screening tool for diagnosis of cutaneous allodynia in patients with viscerally related chronic pelvic pain (CPP).
Study Design
We performed a prospective cohort comparative observational study of referred patients to a gynecology clinic with CPP. A total of 22 females with CPP were compared to 23 pain-free controls and 12 cyclic pain patients. Participants were evaluated by 2 clinicians. The CTA test was performed to detect the appearance of pain in dermatomes of T10-L1.
Results
Interrater reliability resulted in 98% agreement for the 3 study groups. CTA test showed 73% sensitivity and 100% specificity for differentiating patients with CPP from pain-free patients.
Conclusion
The CTA test had excellent interrater reliability and concurrent validity for diagnosis of cutaneous allodynia in CPP patients with visceral diseases versus controls.
Chronic pelvic pain (CPP) causes disability and distress, significantly compromises quality of life, and affects health care costs. The American Congress of Obstetricians and Gynecologists has estimated that 15-20% of women in the age group 18-50 years have experienced pain of >1 year’s duration and 4% continue to have ongoing persistent pain. The Society of Obstetricians and Gynecologists of Canada defines CPP as a pain lasting for ≥6 months, with incomplete relief despite treatment and significantly impaired function at home/work. CPP is a multicausal disease. While a multidisciplinary approach to management of these patients often proves to be effective, it still does not explain why some women continue to experience daily pain that is irresponsive to large doses of pain medications. The concept of the central sensitization may help to explain this medical problem.
Central sensitization seems to be a common feature of chronic pain conditions. The concept of neuroplasticity explains the changes in the function of the central nervous system, particularly at the dorsal root ganglion. The stimuli for the changes are multifactorial. Severe or prolonged visceral pain from organs in the pelvis appears to be one of the significant contributing factors. Visceral pain is typically localized by the brain’s sensory cortex by visceral afferents to the respective spinal cord level. Visceral afferents follow a segmental distribution. Visceral afferent fibers are poorly myelinated and the action potentials may easily spread from them to impact adjacent somatic nerves. As a result, visceral pain may at times be referred to dermatomes that correspond to the impacted somatic nerve fibers. In addition, both peripheral somatic and visceral nerves often synapse in the spinal cord at the same dorsal horn neurons. These neurons, in turn, relay sensory information to the brain. The cortex recognizes the signal as coming from the same dermatomes regardless of its visceral or somatic nerve origin. If noxious stimuli such as inflammatory process following endometriosis or pelvic inflammatory diseases continue for a prolonged period of time, neurons within spinal cord display increased excitability. This is termed “central sensitization.” In the case of the pelvis, it is associated with increased efferent activity that results in aberrant activity in pelvic organs. This persistent central hyperexcitability might cause an increase in perception of pain in visceral organs. Referred pain tends to be localized in areas corresponding to the dermatome and myotome that are supplied by the affected viscus, or remote from the inciting stimulus in an area supplied by the same neural segment as the injured organ. Creation of pain from an innocuous stimulus in the related cutaneous areas is referred to as cutaneous allodynia.
Viscerosomatic pain referral has been evaluated by pain threshold measures and abdominal wall thermography tests. Pain threshold measure tests have been validated with the identification of chronic pain states. Current methods for identifying patients with pain hypersensitivity are sufficiently complex to limit their widespread application in clinical settings. The cotton-tipped applicator (CTA) test has been introduced to identify this group of patients. In an exploratory evaluation of the ability of 3 bedside tests in discriminating visceral disease from nonvisceral disease among women with CPP, the CTA test for cutaneous allodynia appeared to have the greatest likelihood of predicting preexisting or ongoing visceral disease.
The aim of the present study was to assess the test reliability and validity as a screening method by testing the presence of cutaneous allodynia among women with or without CPP. We hypothesized that this test was reliable, feasible, and valid for assessing cutaneous allodynia.
Materials and Methods
This research was carried out as a prospective cohort comparative observational trial. Subjects were recruited from referred patients to Calgary Chronic Pain Clinic and Foothills Medical Center from 2010 through 2011. The date of entry was the date of approval of the ethics application at the University of Calgary. Subjects were invited to participate in the study by a nurse practitioner or a researcher during a clinical consultation for the management of chronic pain. The presence of pelvic visceral disease (eg, endometriosis and adenomyosis) as a possible cause of CPP was determined based on a documented operative record from the health records of the Calgary Health Region of Alberta Health Services. Potential participants were given an explanation of the study and the opportunity to ask questions. Five women declined to participate due to time constraints, severity of their pain, or no specific reasons. After obtaining written informed consent, the participants’ demographic information and medical history were reviewed. Subjects were then allocated into 3 groups based on their description of presence of pain:
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22 women with chronic continuous pelvic pain of ≥6 months’ duration, not controlled with standard treatment.
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12 women with cyclic pelvic pain of ≥6 months’ duration, not controlled with standard treatment (sample of convenience).
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23 women who had no pelvic pain and were referred to Foothills Medical Center for other gynecological reasons.
Exclusion criteria for participation in the study included pregnant/breast-feeding women; women with major medical illnesses such as lupus, diabetes mellitus, or neurologic diseases; and those who did not provide written consent.
CTA test
Two trained clinicians performed the CTA test to determine the presence or absence of CA. Using a table of random numbers, the order of testing was determined. Testing was done during the 5th-10th days of the participant menstrual cycle if menstruating to avoid possible variation in pain sensitivity across different stages of menstrual cycle.
Abdominal test
A CTA was gently passed down from the midclavicular line under ribs on each side of the abdomen to the supra pubic area. It was then directed across the abdomen in the region of the T10-L1 dermatomes. Subjects were instructed to report the appearance of pain by giving signals to clinician. If the sensation suddenly changed and produced a sharp painful sensation despite gentle pressure, the test was considered positive. The participants were asked to score the severity of pain based on visual analog scale. The entire area was marked with a washable marker and a photograph was taken. After the area was washed, the process was repeated by the second observer. The time frame for performing the evaluations by the 2 raters was between 5-15 minutes. For a video presentation of the abdominal test, refer to “Demonstration of Cutaneous Allodynia in Association with Chronic Pelvic Pain” by Jarrell.”
The primary outcome was measured based on a dichotomous “yes/no” response.
Test validity
Concurrent validity assessment was based on observing the rates of cutaneous allodynia among those with continuous pain due to pelvic visceral disease and those with no pain. For further assessment of validity the rates of cutaneous allodynia between pain subjects and those with cyclic pain was assessed.
Test reliability
Interrater reliability was measured based on the raters’ agreement on the presence or absence of cutaneous allodynia in each of the 3 groups.
Based on preliminary data and clinical experience, it was expected that 80% of women with continuous pain would have a positive CTA test and that no one without pain would show a positive CTA test. Assuming a significance level of .05, a sample size of 20 patients in each group would give >95% power to detect such a difference. Descriptive statistics were used to summarize participant characteristics. The Mann-Whitney U test was used to compare duration of pain and pain intensity between the continuous and cyclic pain groups.
To assess concurrent validity, the χ 2 test was used to compare the CTA test’s ability to distinguish between women with continuous pelvic pain vs those with no pelvic pain, and women with continuous pain vs cyclic pain. Sensitivity and specificity of the CTA test was reported with the corresponding exact 95% confidence intervals. Interrater reliability was measured using the proportion of agreement and McNemar test. Software (SAS 9.2; SAS Institute Inc, Cary, NC) was used for analysis.
Results
Of the 64 women enrolled in the study, 7 women were excluded from the continuous pain group due to causes other than visceral disease such as motor vehicle accident, trauma, or complications of their surgery. A total of 57 women were included in the analysis.
Population demographics are listed in Table 1 . The mean age of participants, gravidity, and parity in the 3 study groups were similar. The median duration of pain was comparable in the continuous group and the cyclic pain group (6 vs 5 years). Patients in the continuous pain group had higher baseline pain intensity, all >5 on a visual analog scale of 0-10.
| Characteristic | Continuous pain (n = 22) | Cyclic pain (n = 12) | No pain (n = 23) |
|---|---|---|---|
| Mean age, y (SD) | 35 (10) | 37 (8) | 39 (8) |
| G0, P0 | 11 (50%) | 8 (67%) | 8 (35%) |
| G>0, P0 | 1 (5%) | 0 (0%) | 4 (17%) |
| G>0, P>0 | 10 (45%) | 4 (33%) | 11 (48%) |
| Median duration of pain, a y | 6 (IQR 10) | 5 (IQR 8) | N/A |
| Range, 2–17 | Range, 1–30 | ||
| Median pain intensity on VAS | 6 (IQR 1) | 5 (IQR 2) | N/A |
| Range, 5–8 | Range, 4–10 |
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