Problems in establishing the medical expert systems CADIAG-1 and CADIAG-2 in rheumatology.

CADIAG-1 and CADIAG-2 are medical expert systems with applications in rheumatology, gastroenterology, and hepatology. CADIAG-1 is based on a symbolic logic representation of medical relationships between symptoms, signs, or findings and diseases. Definite relationships (obligatory occurrence, confirming, and excluding) as well as uncertain relationships (facultative occurrence and not confirming) are applied to confirm or exclude diagnoses and to establish diagnostic hypotheses. CADIAG-2 employs fuzzy set theory and fuzzy logic to formalize medical entities and relationships. The medical concept of confirming or excluding diagnoses is identical to that of CADIAG-1, but diagnostic hypotheses are generated differently. Here, a documentation of medical relationships allowing gradual transitions from "always" to "never" for the frequencies of occurrence of symptoms with and from "strong" to "weak" for their strengths of confirmation for diseases leads to strongly or weakly supported diagnostic hypotheses in the actual case. Tests with 322 real patient cases from a rheumatological hospital, each including between 500 and 700 symptoms, signs, and findings, were carried out. The percentage of cases diagnosed correctly is about 80%. Problems and pitfalls that became apparent in the evaluation of the cases are shown and discussed.