Bedside testing for chronic pelvic pain: discriminating visceral from somatic pain

Jarrell J, Giamberardino MA, Robert M, Esfahani MN. Pain research and treatment. 2011; 2011: article ID 692102.

Cindy Neville, PT, DPT, WCS- January 9, 2013

Primary Aim: To determine the ability of 3 simple bedside tests of cutaneous allodynia, myofascial pain, and reduced pain thresholds to differentiate women with visceral and somatic conditions associated with their chronic pelvic pain.

Background: The concepts of referred visceral pain to a specific cutaneous location and that an irritable focus in certain tissues could be responsible for such localization have been investigated for many years. For example, stimulation of the ureter or the pelvis of the kidney was found to cause a contraction of the muscles of the abdominal wall on the stimulated side and remain contracted for a period of time (Head 1809, Mackenzie 1909).  Visceral disease is known to contribute to the development of myofascial trigger points in biliary, cardiac, and renal disease, and in endometriosis and interstitial cystitis. In the female reproductive system the relationship of the referral of pain through viscerosomatic processes is complex. As the visceral afferents are greatly outnumbered by somatic afferents, there is considerable merging of signals ( viscerosomatic convergence) which makes the specificity of organ of origin a complex message for the central nervous system. This means that pain originating from pelvic organs may not be identified with accuracy. This can lead to situations where investigations and surgery are repeated and in some cases extensively.

Subjects:   81 females referred by FP of GYN with CC of CPP > 6 months. Subjects were characterized as having known visceral disease (n=62) or known somatic pain (n = 19) (Table 1) Information on prior treatments for pain was not collected. Mean age = 33.9 +/- 1.2 , gravidity mean  = 1, parity mean = .82 , mean duration of pain 4.3 years.

Operational definitions: Visceral disease as a cause of the woman’s chronic pelvic pain was pain that clinically appeared to be originating from visceral tissues. This was based on the clinical history, physical examination, referral information, and available documentation from the health records. Women with somatic pain did not have a history of visceral disease but did have prior lower genital tract surgery, lower genital tract  obstetrical trauma, or musculoskeletal disorders of the pelvic bones from prior motor vehicle  accidents.

Methods:   Exploratory cross-sectional study approved by ethics application at The University of Calgary. Clinical testing, pain evaluation, and medical history were all done at the same test session by a single unblinded observer.

• Test 1: Testing for cutaneous allodynia involved the use of a cotton-tipped culture stick . The culture stick is drawn down from the upper abdomen into the area identified as painful by the woman. In the presence of cutaneous allodynia there is a sharply demarcated area in which this sensation goes from nonpainful to a painful sensation. The area can be variable in size, from dime-sized areas on one or both sides of the lower quadrants to broad expanses of the lower abdomen. The usual location is in the region of the dermatomes of T12- L1 located centrally in the abdomen. The same approach is undertaken on the perineum by drawing the cotton-tipped culture stick across the buttocks in a horizontal fashion to identify mainly the S3 dermatome. Preliminary studies of  the validity have demonstrated blinded interrater reliability of 98%.
• Test 2: Examination for myofascial trigger points : Within the areas of cutaneous allodynia, one can appreciate increased muscle tone and myofascial trigger points. The examination for myofascial trigger points has been validated. These are confirmed by an examination of the abdominal wall and perineum within the area of cutaneous allodynia in which a small nodule can be palpated. When this nodule is pressed, it causes severe pain with referral of pain into the back, legs, chest, and pelvis. The sensation of the pain has commonly the same characteristic as the chronic pain being experienced. When the pressure is released, the pain resolves. The areas tested for this study included the right- and left-upper abdominal and the right- and left-lower abdominal quadrants. In almost all cases, the myofascial trigger points were identified in the right- and/or left-lower quadrants near the junction of the external oblique and rectus abdominus muscles. Testing of the presence of a trigger point on the perineal body was also performed. Testing of the levator ani muscle internally was not performed.
• Pain threshold evaluation involved the use of the Von Frey electroanesthesiometer (IITC Life Science). This test has been validated for the assessment of pain. It was initially applied to the deltoid muscle as a reference point or internal control. Pressure of 100 g that did not produce pain was taken as a negative test on the deltoid and other areas. Measurements of pain threshold were then taken in the right-upper and right-lower abdominal quadrants and the left-upper and left-lower abdominal quadrants and theperineal body which is located on the perineum just distal to the hymen on the posterior fourchette. On the perineum, the algometer was applied to the affected muscle by applying the instrument to a sterile culture stick. In all testing the pressure was gradually applied to the affected area until the woman identified a painful sensation or until a maximum of 100 g pressure was obtained. Pain thresholds lower than 100 g were identified as demonstrating reduced pain thresholds. The measurement was then calculated as a percentage of the deltoid measurement.

Outcomes:  The presence or absence of cutaneous allodynia, myofascial dysfunction, and reduced pain thresholds was evaluated in relation to the clinical diagnosis to determine the sensitivity, specificity, positive predictive values, negative predictive, likelihood ratios, and odds ratios of the tests. Categorical results were evaluated with contingency methods and non-normally distributed variables were compared using the Mann Whitney U test. Statistical analysis was done using SPSS. Diagnostic test properties were evaluated using tests for sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio, and odds ratio with 95% confidence intervals (95% C.I.)

Results: 

Pain Classification Results: Of the 62 women with visceral pain, the following conditions were identified: endometriosis-36; pelvic inflammatory disease-2; adhesions-5; interstitial cystitis-1; dysmenorrhea-11; ovarian cyst removal-4, fibroid-2; tubal ligation-1. The 19 women with somatic causes of pain had  clinical histories indicating trauma to the lower genital tract or pelvis from surgery or motor vehicle accidents. Four women were identified as having both visceral and somatic causes of pain.

Patient characteristics: Women with visceral pain were younger (P < 0.01), had fewer pregnancies (P < 0.001), and reported a longer duration of pain (P < 0.01) when compared to women with somatic pain . Women with visceral disease had a greater number of prior laparoscopies (P < 0.001) but similar number of laparotomies when compared to women with somatic pain (Table 1).

Test utility for discriminating visceral vs somatic sources of pain: Abdominal and perineal cutaneous allodynia and abdominal myofascial trigger points were found to significantly discriminate visceral from somatic sources of pain. Perineal myofascial trigger points and reduced pain thresholds did not discriminate visceral from somatic sources of pain. The likelihood and the odds ratios of a positive finding of abdominal and perineal cutaneous allodynia and abdominal trigger points significantly indicated a positive identification of a visceral source of pain compared to a somatic source of pain (P < 0.001) (Table 3).

Pain thresholds: A comparison of the numeric reduction in pain thresholds identified using the Von Frey electroanesthesiometer demonstrated significantly lower pain thresholds in the right- and left-lower quadrants of women with visceral pain compared to women with somatic pain (P < 0.05) (Table 4). There were no differences in mean pain thresholds in the deltoid region, upper abdominal quadrants, or perineum.

Strengths:  Tests are simple to perform, based on validated methods, do not require sophisticated equipment. Tests are acceptable to women.

Weakness: Bias in interpretation of test findings by un-blinded observer, small sample size, allocation to visceral vs somatic based on documented history. Women with somatic course of pain included women with lower genital tract pelvic trauma which could also be visceral pain. Confounding internal validity issue that trigger points themselves are somatic sources of pain.

Conclusions: Testing for abdominal and perineal cutaneous allodynia and for abdominal myofascial trigger points can discriminate visceral from somatic sources of pain.

Implications for clinical practice: PTs can use these tests in diagnosis and treatment planning for patients with CPP.

Discussion Questions:

·         How would you use these tests in clinical practice

·         Would positive testing alter your intervention and treatment planning? If yes, how so?

·         What should we think about the 4 patients with both visceral and somatic pain diagnoses?

·         What do you think is the importance of the lower pain thresholds in the lower quadrants?