Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Diagnostic Value of Pathergy Phenomenon in Behcet's Disease.

Davatchi,  Fereydoun, Chams-Davatchi,  Cheyda, Shahram,  Farhad, Sadeghi Abdollahi,  Bahar, Nadji,  Abdolhadi, Akhlaghi,  Massoomeh, Faezi,  Tahereh

Background:

Pathergy phenomenon (PP) is used for the diagnosis of Behcet's Disease (BD). It is an important criterion of many classification/diagnosis criteria. The sensitivity of PP was 83% in Russia, 77% in Morocco, 71% in Iraq, 62% in China and Egypt, 61.5% in Iran, 55% in Germany, 44% in Japan, and 18% in Saudi Arabia. The sensitivity of PP is changing over the time. It has changed in Iran from 71.8% for the first 1000 patients to 33.9% for patients 5000 to 6000. The aim of this study was to look for the diagnostic value of PP in the present time, and its change over the past 35 years.

Patients and Methods:

The Behcet's Disease registry, has the data of 6607 BD and 4292 Control patients from the past 35 years. Patients were divided in 4 groups of 1650 BD and 1073 controls. Sensitivity, Specificity, Positive and Negative Predictive Value (PPV & NPV), Positive and Negative Likelihood Ratio (PLR & NLR), Diagnostic Odds Ratio (DOR), and Youden's Index (YI) were calculated. The first and the 4th quartiles were compared.

Results:

Positive PP changed from 64.2% to 35.8% (1st and 4th quartiles) in BD and from 13.4% to 1.6% in control patients (Table 1). Sensitivity, specificity, PPV, NPV, PLR, NLR, DOR, and YI are shown in Table 2.

Table 1. Details of Behcet's Disease and control patients

PatientsFirst GroupSecond GroupThird GroupFourth Group
BD Patients1–16501651–33003301–49504951–6607
PP Done1580163916221643
Positive PP1014971820588
% Positive64.259.250.635.8
95% CI61.8–66.556.8–61.548.2–53.133.5–38.1
Control Patients1–10731074–21462147–32193220–4292
PP Done106910699801061
Positive PP143961017
% Positive13.49.01.01.6
95% CI11.5–15.67.4–10.90.5–1.91.0–2.6

Table 2. Performance and Diagnostic value of Pathergy Test

Patients and ControlsFirst GroupSecond GroupThird GroupFourth Group
Sensitivity64.259.250.635.8
Specificity86.691.099.098.4
Positive Predictive Valuea82.786.898.195.7
Positive Predictive Valueb 33%70.276.496.191.7
Positive Predictive Valuec 0.08%0.380.523.891.76
Negative Predictive Valuea82.769.066.760.5
Negative Predictive Valueb 33%83.181.980.375.7
Negative Predictive Valuec 0.0899.9799.9699.9699.95
Positive Likelihood Ratio4.86.650.622.4
Negative Likelihood Ratio0.410.450.50.65
Diagnostic Odds Ratio11.614.7101.434.3
Youden's Index0.50.50.50.34
a: Predictive Value of PP without taking in account the prevalence of Behcet's diseaseb: Predictive Value calculated for the Behcet's Disease clinic at RRC (prevalence of BD: 33%)c: Predictive Value calculated for the population of tran (prevalence of BD: 0.08%)

Discussion:

The sensitivity of PP decreased while the specificity increased. The difference was statistically significant (Table 2).

PPV shows the probability that the positive test is true positive. PPV is influenced by the prevalence of the disease in the tested population. The prevalence of BD in Iran is 0.08%. In BD clinic, 1/3rd of new patients have BD. PPV improved from 0.38% to 1.76 (population) and from 70.2% to 91.7% in BD Unit (between 1st and 4th quartile). Although the sensitivity of PP has decreased over the time, its value as a diagnostic test, when positive, has improved. NPV shows the probability that a negative test is truly negative. NPV lost a little in the BD Clinic, going from 83.1% to 75.7% (Table 2).

PLR shows the odds of having the disease. PLR improved from 4.8 to 22.4 (1st to 4th quartile), meaning the risk of having BD with positive PP is 22.4 times. The NLR deteriorated from 0.41 to 0.65, meaning the error rate of not having BD increased from 41 to 65%.

The diagnostic odds ratio (DOR) combines the results of PLR and NLR, A value of 1 means no discrimination between patients and controls. Higher values mean better discrimination. DOR improved from 11.6 to 34.3 (from 1st to 4th quartile).

Youden's Index (YI) shows the accuracy of PP. Zero is the worse and one the best. The YI decreased from 0.5 to 0.34, showing a deterioration of precision rate over the time.

Conclusion:

PP improved its diagnostic value.

To cite this abstract, please use the following information:
Davatchi, Fereydoun, Chams-Davatchi, Cheyda, Shahram, Farhad, Sadeghi Abdollahi, Bahar, Nadji, Abdolhadi, Akhlaghi, Massoomeh, et al; Diagnostic Value of Pathergy Phenomenon in Behcet's Disease. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1289
DOI: 10.1002/art.29055

Abstract Supplement

Meeting Menu

2010 ACR/ARHP