DIALOG: A Model Of Diagnostic Logic For Internal Medicine

A system f o r computer a s s i s t e d m e d i c a l d i a g n o s i s has been developed, which i n c o r p o r a t e s an i n n o v a t i v e model o f d i a g n o s t i c l o g i c . A s u p p o r t i n g m e d i c a l d a t a base has a l s o been assembled, now c o m p r i s i n g a p p r o x i m a t e l y f i f t y p e r c e n t o f t h e major diseases o f i n t e r n a l m e d i c i n e . Using weighted a s s o c i a t i o n s between disease e n t i t l e s and t h e i r m a n i f e s t a t i o n s , and employing a powerf u l a t t e n t i o n f o c u s i n g h e u r i s t i c , t h e system has demonstrated competence I n d e a l i n g w i t h d i f f i c u l t c l i n i c a l problems i n v o l v i n g m u l t i p l e diagnoses. 1 . I n t r o d u c t i o n 1.1. I n t e r n a l Medicine as a Task Environment f o r A r t i f i c i a l I n t e l l i g e n c e A t f i r s t g l a n c e , the t a s k environment o f i n t e r n a l medicine might appear t o b e e m i n e n t l y s u i t a b l e f o r a t t a c k b y means o f t h e s t s t e s p a c e methods (1) o f a r t i f i c i a l i n t e l l i g e n c e . A medi c a l problem may be c h a r a c t e r i s e d In terms of a n i n i t i a l s t a t e ( d i s e a s e ) , a g o a l s t a t e ( h e a l t h ) , and a c o l l e c t i o n o f a v a i l a b l e o p e r a t o r s ( d r u g s , s u r g i c a l procedures, d i e t s , e t c . ) b y which one s t a t e may be transformed i n t o a n o t h e r . The main d i f f i c u l t y w i t h t h i s view o f t h e t a s k i s t h a t o r d i n a r i l y , evidence a v a i l a b l e a t the o u t set p r o v i d e s o n l y a p a r t i a l d e s c r i p t i o n o f t h e i n i t i a l s t a t e o f a med i c a l problem. While soc a l l e d ' p r e s e n t i n g s i g n s and symptoms' may be s u g g e s t i v e of one or more abnormal or p a t h o l o g i c a l c o n d i t i o n s , I n most cases, c o n c l u s i v e evidence c o n c e r n i n g the u n d e r l y i n g d i s o r d e r i s not a v a i l a b l e . Because he can be much more s e l e c t i v e in the choice of t h e r a p e u t i c measures when a t t e m p t i n g t o t r e a t t h e cause r a t h e r than i t s m a n i f e s t a t i o n s , the c l i n i c i a n i s g e n e r a l l y o b l i g e d t o f o r m u l a t e a model, c o m p r i s i n g one or more hypothesized abnormal o r p a t h o l o g i c a l c o n d i t i o n s , a s a b a s i s f o r c l i n i c a l problem s o l v i n g . T h i s process of g e n e r a t i n g and t e s t i n g hypotheses w i t h r e s p e c t to unobserved perhaps u n o b e e r v a b l e — p a t h o l o g i c a l c o n d i t i o n s I s t h e essence o f medical d i a g n o s i s . Because t h i s t a s k is one of 'problem f i n d i n g ' o r 'problem f o r m u l a t i o n , ' not 'problem s o l v i n g ' a s t h i s t e r m i s g e n e r a l l y c o n s t r u e d , I t i s not c l e a r t h a t t h e s o l u t i o n o r i e n t e d h e u r i s t i c procedures o f a r t i f i c i a l i n t e l l i g e n c e have any b e a r i n g o n t h i s e s s e n t i a l aspect o f the m e d i c a l t a s k environment. I n c e r t a i n a p e c l a l cases, where t h e d i a g n o s t i c t a s k can b e t a k e n t o b e t h a t o f i d e n t i f y i n g the presence o f a s i n g l e c l i n i c a l problem, any o f a host o f d e t e r m i n i s t i c o r p r o b a b i l i s t i c ' r e c o g n i z e r s ' can b e employed t o d e a l w i t h t h e problem. (See f o r example: Ledley and Lusted ( 2 ) , Gorry and B a r n e t t ( 3 ) , B l e l c h ( 4 ) . ) Such methods a r e of v e r y l i m i t e d scope, however, a s t h e y r e s t o n t h e assumption t h a t the c l i n i c a l cases to be analyzed are 'pure' i . e . , t h e r e are no erroneous data (sometimes c a l l e d r e d h e r r i n g s ) t o b e d e a l t w i t h , and o n l y one c l l n i c o p a t h o l o g i c a l d i a g n o s i s to be d i s c e r n e d in esch case. I n t h e r e a l w o r l d o f i n t e r n a l m e d i c i n e , these assumptions a r e r a r e l y s a t i s f i e d . Nonet h e l e s s , t h e s k i l l e d c l i n i c i a n manages t o s o r t o ut the f a c t s of s case, d i s r e g a r d i n g some, w h i l e on the b a s i s of o t h e r s f o r m u l a t i n g a c l i n i c a l p i c t u r e t h a t may comprise a number o f i n t e r r e l a t e d o r d i s t i n c t disease e n t i t i e s . I n what f o l l o w s , w e d e s c r i b e and i l l u s t r a t e a model of the d i a g n o s t i c process ( c a l l e d DIALOG, f o r D I A g n o s t i c LOGic) t h a t was designed t o mimic t h e d a t a s t r u c t u r e s and r e a s o n i n g processes o f t h e s k i l l e d c l i n i c i a n . The process employs a n o v e l h e u r i s t i c procedure f o r r a n k i n g and p a r t i t i o n i n g o f d i a g n o s t i c I n f e r e n c e s , w h i c h enables c o n s t r u c t i o n o f c l i n i c a l l y r e l e v a n t d i a g n o s t i c models even i n t h e presence o f e r r o n e ous and m i s l e a d i n g d a t a . Using an e x t e n s i v e m e d i c a l data base which encompasses a p p r o x i m a t e l y f i f t y p e r c e n t o f t h e major diseases o f I n t e r n a l m e d i c i n e , the DIALOG procedure has a c c u r a t e l y analyzed many complex, r e a l w o r l d c l i n i c a l problems, I n v o l v i n g aa many aa f i v e d i s t i n c t disease e n t i t i e s . I n t h e f o l l o w i n g s e c t i o n s , w e d e s c r i b e f i r s t t h e l o g i c o f t h e d i a g n o s t i c process and t h e s t r u c t u r e o f m e d i c a l knowledge t h a t u n d e r l i e s t h e DIALOG d a t a base. There f o l l o w s s d e s c r i p t i o n o f t h e DIALOG p r o c e d u r e , and an i l l u s t r a t i o n o f t he system's b e h a v i o r .