A LOGISTIC REGRESSION MODEL TO PREDICT NODAL MALIGNANCY. AMONG CASES WITH LYMPHADENOPATHY. Gaafar M. Malik, MRCP; Mostafa A.
A LOGISTIC REGRESSION MODEL TO PREDICT NODAL MALIGNANCY AMONG CASES WITH LYMPHADENOPATHY Gaafar M. Malik, MRCP; Mostafa A. Abolfotouh, MPH, DrPH; Suliman Jastania, FRCSEd; Nader Morad, FCAP; Eldawi N. Eltayeb, FRCSI, FRCSEd; Gulam Saydain, MD
Background: Peripheral lymphadenopathy can be caused by benign and malignant diseases. In this logistic regression model, we attempted to identify the clinical findings predicting high probability of nodal malignancy. Materials and Methods: Two hundred and twenty cases diagnosed by peripheral lymph node biopsy were studied. Of these, 164 had benign lymph node pathology, while the other 56 were malignant. The patients’ medical charts were reviewed and a logistic regression model used to identify physical signs and simple investigations that will predict nodal malignancy. Results: Hard lymph node consistency, negative Mantoux test and positive abdominal ultrasound (showing hepatosplenomegaly with or without lymphadenopathy) were found to correlate with a higher probability of nodal malignancy. Conclusion: A logistic regression model is proposed to calculate the probability of lymph node malignancy at different ages and both sexes in relation to lymph node consistency, Mantoux test and abdominal ultrasound results. Ann Saudi Med 1998;18(6):518-521. Key Words: Lymph node, Mantoux test, abdominal ultrasound, hard node.
Peripheral lymphadenopathy can be caused by benign and malignant diseases. 1 The most common benign causes include granulomatous lymphadenitis and reactive lymphoid hyperplasia, while the most common malignant causes include lymphoma and metastatic cancers. 2 Although lymph node biopsy is the final method to differentiate between benign and malignant nodes, several investigations are known to be helpful, including ultrasound and CT of nodes. 3,4 In this study, by reviewing the histopathological results of 220 lymph node biopsies and correlating the result with clinical findings and simple investigations, we attempted to develop a model predicting nodal malignancy from the age and sex of the patient, consistency of lymph node, result of Mantoux test and abdominal ultrasound. Materials and Methods Cases of lymphadenopathy seen in Asir Central From the Departments of Medicine (Dr. Malik), Family and Community Medicine (Dr. Abolfotouh), Surgery (Dr. Jastania), and Pathology (Dr. Morad), College of Medicine, King Saud University, and the Departments of Surgery (Dr. Eltayeb) and Medicine (Dr. Saydain), Asir Central Hospital, Abha, Saudi Arabia. Address reprint requests and correspondence to Dr. Malik: Associate Professor of Medicine, College of Medicine, King Saud University, Abha Branch, P.O. Box 641, Abha, Saudi Arabia. Accepted for publication 7 July 1998. Received 24 March 1998.
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Hospital, Abha, in Southwest Saudi Arabia during the period 1992-1995 inclusive, were studied retrospectively. A total of 220 cases in which lymph node biopsy was done with an available histopathological report were included in the study. Of the number, 113 were males, with a mean age±SD of 31.84±21.39 years (range 4 months to 100 years). One hundred and sixty-four patients were diagnosed as benign, with cases of caseating granuloma (72), reactive hyperplasia (71), noncaseating granuloma (5) and nonspecific lymphadenitis (16). The remaining 56 were malignant, including non-Hodgkin’s lymphoma (19), Hodgkin’s lymphoma (17) and metastatic carcinoma (20). The patients’ charts were reviewed for demographic data, duration of lymphadenopathy, site of lymph nodes, their consistency, presence of hepatosplenomegaly, result of Mantoux test and abdomen ultrasound. The Mantoux test was performed by injecting 5 tuberculin units of PPD intradermally, and the result measured after 72 hours. A result of 10 mm or more was considered positive. A positive abdominal ultrasound was the one showing hepatosplenomegaly with or without lymphadenopathy. Data was analyzed using SPSS for Windows ® statistical software. Chi-squared test was applied to compare categorical data, and Mann-Whitney test for comparison of quantitative data. Significance was assumed if P-value was less than 0.05.
LOGISTIC REGRESSION MODEL
Logistic regression model was applied using the Wald statistical technique to show the value of the above clinical findings and investigations in predicting nodal malignancy. The logistic regression analysis is a statistical technique through which one can examine the relationship between a dependent variable and a set of independent variables, and select the independent variables which could provide the best prediction possible of the dependent variable and exclude the others with no association. The following variables were used in this model. a) Dependent variables: y=histopathology of lymph node, coded as follows: 0=non-malignant, 1=malignant. b) Independent variables, x as follows: 1. x1 = dummy variable used for sex as follows: x1, 0 =female. x1, 1 =male. 2. x2= dummy variable for age in years as follows: x2, 0 = age 60 years or less. x2, 1 = age more than 60 years. 3. x3 = dummy variable for Mantoux test as follows: x3, 0 = negative Mantoux. x3, 1 = positive Mantoux. 4. x4 = Dummy variable for nodal consistency as follows: x4, 0 = not hard. x4, 1 = hard 5. x5= Dummy variable for ultrasound abdomen as follows: x5, 0 = normal. x5, 1 = abnormal. The general form of the regression model is as follows: z= ß0+ ß1x1+ ß2x2 ……. + ßpxp where z = the linear combination, ß 0 = constant. ß 1, ß 2, ……. ßp are partial regression coefficients. x1, x2, …….xp are the independent variables. Results Table 1 shows the univariate association of nodal malignancy with different demographic and clinical findings. It shows a significant association between nodal malignancy and each of the five variables, i.e., age (P
