# (Ijcsis) International Journal Of Computer Science And Information Security, Vol. 7, No. 2, 2010 Integration Of Rule Based Expert Systems And Case Based Reasoning In An Acute Bacterial Meningitis Clinical Decision Support System

Mariana Maceiras Cabrera Departamento de Informática y Ciencias de la Computación Universidad Católica del Uruguay Montevideo, Uruguay 
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Abstract—This article presents the results of the research carried out on the development of a medical diagnostic system applied to the Acute Bacterial Meningitis, using the Case Based Reasoning methodology. The research was focused on the implementation of the adaptation stage, from the integration of Case Based Reasoning and Rule Based Expert Systems. In this adaptation stage we use a higher level RBC that stores and allows reutilizing change experiences, combined with a classic rule-based inference engine. In order to take into account the most evident clinical situation, a pre-diagnosis stage is implemented using a rule engine that, given an evident situation, emits the corresponding diagnosis and avoids the complete process.

Keywords-Case-Based Reasoning; Medical Diagnosis; Expert Systems; Acute Bacterial Meningitis 

## I. Introduction

Clinical Decision Support Systems (hereafter CDSSs) have become paramount in the medical environment, providing support to the clinical expert in the diagnosing process, mainly assisting the analysis and synthesis of bulk information in little time. These systems enable the reduction of the intrinsic degree of uncertainty that any decision-making process in the medical environment entails. [1], [2] 
Several aspects related to a specific kind of CDSS, Medical Diagnostic Systems (hereafter MDSs), will be addressed throughout this document. From a set of symptoms and signs shown by the patient, the MDS are capable of **suggesting** a set of differential diagnoses, possibly with a certainty degree associated to each of them. [1], [3] 
While developing MDSs, either in their construction and application, several problems arise: 1) Representation of the domain knowledge; 2) Processing of such knowledge; 3) 
Obtaining results that are accurate enough and 4) Presentation of the results to the user, and their explanation. Each of these problems is solved in a particular way, depending on the method applied to the development of the system. In this document is presented an alternative way to solve these problems using Case Based Reasoning. [1], [4] 
Ernesto Ocampo Edye Departamento de Informática y Ciencias de la Computación Universidad Católica del Uruguay Montevideo, Uruguay This research is focused on the development of an Acute Bacterial Meningitis MDS integrating Case Based Reasoning (hereafter CBR) with Rule Based Expert Systems (hereafter RBR).

This document is organized in the following way: in Section 2 is presented the case study used in the research: Diagnosis of Acute Bacterial Meningitis, followed in section 3 by the presentation of the addressed problem. Section 4 presents a brief summary of state-of-the-art techniques and referred applications. Afterwards, section 5 describes the proposed computer solution in detail, while in section 6 is described the composition of the knowledge base, which represents reality and is used in simulations, and the way it was built. Section 7 presents the results of the system's performance assessment and section 8 outlines the conclusions of this work. 

II. CASE STUDY: DIAGNOSIS OF ACUTE BACTERIAL 
MENINGITIS
The medical diagnosing task consists in "translating" the relation between a set of signs and symptoms found in a patient, and the possible pathologies she or he might suffer from. [3], [1] This work addresses the medical diagnosis of the disease known as Acute Bacterial Meningitis (hereafter ABM). 

ABM is an infectious disease caused by bacteria that attack the meninges (a membrane system that covers the Central Nervous System - brain and spinal cord). The meningitis is an inflammatory process of the leptomeninges (pia mater and arachnoid mater), and the cerebrospinal fluid (CSF) contained inside them [5]. The Meningitis poses a great threat to optical, facial and auditory nerves, and other kinds of neurologic sequels. 

In this research we have taken as a reference a subset of the typical signs and symptoms of this disease - a total of 81 symptoms have been considered - which are: convulsions, depression, fever, hypertense fontanelle, nape stiffness, trunk stiffness, skin purpuric syndrome, vomits, somnolence, 