This transcript is part of
Pople, H. E., Jr. "Heuristic Methods for Imposing Structure on Ill-Structured Problems: The Structuring of Medical Diagnostics." Chapter 5 in Szolovits, P. (Ed.) Artificial Intelligence in Medicine. Westview Press, Boulder, Colorado. 1982.
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(DOCTOR)
This command is used to invoke the DOCTOR program, which embodies the interactive diagnostic procedure of INTERNIST-I; the program is written in a dialect of LISP called INTERLISP.
INTERNIST-I consultation SUMEX-AIM Version
PLEASE ENTER FINDINGS.
After the initial prompt PLEASE ENTER FINDINGS, the person using the system enters whatever positive findings he chooses to divulge. The program prompts with "*" to request additional input until the respondent types "GO"; after which INTERNIST-I commences the task definition procedure described in the previous section. Had the user wanted to enter negative findings during this initial exchange, he could have responded "DENY" to the prompt, causing subsequent entries to be interpreted as negative results.
*SEX MALE *AGE 26 TO 55 *RACE WHITE *ALCOHOLISM CHRONIC HX *EXPOSURE TO RABBITS OR OTHER SMALL MAMMALS *FEVER *MYALGIA *LEG <S> WEAKNESS BILATERAL *LEG <S> WEAKNESS PROXIMAL ONLY *PRESSURE ARTERIAL SYSTOLIC 90 TO 110 *PRESSURE ARTERIAL ORTHOSTATIC HYPOTENSION *TACHYCARDIA *JAUNDICE *ANOREXIA *DIARRHEA ACUTE *FECES LIGHT COLORED *VOMITING RECENT *LIVER ENLARGED SLIGHT *SKIN SPIDER ANGIOMATA *SKIN PALMAR ERYTHEMA *OLIGURIA HX *UREA NITROGEN BLOOD 60 TO 100 *CREATININE BLOOD INCREASED *WBC 14000 TO 30000 *PLATELETS LESS THAN 50000 *GO
Manifestations are expressed by means of precise sequences of terms in a controlled vocabulary; there are presently approximately 3500 vocabulary items that can be used to describe positive and negative findings.
DISREGARDING: EXPOSURE TO RABBITS OR OTHER SMALL MAMMALS, LEG <S> WEAKNESS BILATERAL, LEG <S> WEAKNESS PROXIMAL ONLY, PRESSURE ARTERIAL ORTHOSTATIC HYPOTENSION, CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: AGE 26 TO 55, SEX MALE, ANOREXIA, MYALGIA, VOMITING RECENT, FECES LIGHT COLORED, FEVER, JAUNDICE, LIVER ENLARGED SLIGHT, SKIN PALMAR ERYTHEMA, SKIN SPIDER ANGIOMATA, WBC 14000 TO 30000, PLATELETS LESS THAN 50000
RULEOUT: HEPATITIS CHRONIC ACTIVE, ALCOHOLIC HEPATITIS, HEPATIC MILIARY TUBERCULOSIS, MICRONODAL CIRRHOSIS <LAENNECS>, HEPATITIS ACUTE VIRAL
At this point, INTERNIST-I reports concerning the initial differential diagnosis that will be the focus of problem solving attention. Three lists are displayed, labeled respectively DISREGARDING, CONSIDERING, and RULEOUT. The CONSIDERING list identifies those positive findings whose differential diagnostic tasks were combined in coming to the differential diagnostic focus, which is described by the RULEOUT list. The DISREGARDING list tells what positive findings are not consistent with the differential diagnosis as formulated and are therefore being disregarded for the moment; they will, however, be attended to in due course. The keyword RULEOUT indicates what strategy INTERNIST-I is going to pursue relative to this task definition: in this case, as in any case when the differential list contains five or more alternatives, the program will try to find questions to ask which, if the response is negative, will serve to downgrade the score of one or more diagnoses on the list. While pursuing a RULEOUT strategy, the program limits the questions to be asked to items of information obtainable via history or physical exam.
Please Enter Findings of JAUNDICE HX *GO
There are two formats used for asking questions. In the preceding line, the user is asked to provide any data that might be available within the specified category of findings. Actually. the respondent is free to enter whatever positive or negative data desired and is not constrained to the category mentioned in the query. In this case, the user chose to respond GO; this passes the initiative back to the program, which then typically follows up on the general question by asking about the specific finding of that category for which it particularly wants a YES or NO answer.
JAUNDICE INTERMITTENT HX ? NO
If the respondent did not have any information concerning this direct question, he could have answered N/A-meaning not available.
Please Enter Findings of APPETITE/WEIGHT *GO
WEIGHT LOSS GTR THAN 10 PERCENT ? NO
The program asks a series of questions that have been selected in accordance with its problem solving strategy, then repeats the scoring and partitioning processes of the task definition procedure.
DISREGARDING: EXPOSURE TO RABBITS OR OTHER SMALL MAMMALS, LEG <S> WEAKNESS BILATERAL, LEG <S> WEAKNESS PROXIMAL ONLY, PRESSURE ARTERIAL ORTHOSTATIC HYPOTENSION, CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 50 TO 100
CONSIDERING: AGE 25 TO 55, SEX MALE, ANOREXIA, MYALGIA, VOMITING RECENT, FECES LIGHT COLORED, FEVER, JAUNDICE, LIVER ENLARGED SLIGHT, SKIN PALMAR ERYTHEMA, SKIN SPIDER ANGIOMATA, WBC 14000 TO 30000, PLATELETS LESS THAN 50000
RULEOUT: HEPATITIS CHRONIC ACTIVE, ALCOHOLIC HEPATITIS, HEPATIC MILIARY TUBERCULOSIS, HEPATITIS ACUTE VIRAL, INFECTIOUS MONONUCLEOSIS
Except for the substitution of an acute process (infectious mononucleosis) for a chronic one (micronodal cirrhosis), this differential diagnosis is not significantly changed from the initial formulation. Note that the possibility of cirrhosis has not actually been ruled out; it has merely dropped out of sight because its score has fallen below the threshold used by the task definition procedure.
Please Enter Findings of PAIN ABDOMEN *GO
ABDOMEN PAIN GENERALIZED ? NO
ABDOMEN PAIN EPIGASTRIUM ? NO
ABDOMEN PAIN NON COLICKY ? NO
ABDOMEN PAIN RIGHT UPPER QUADRANT ? NO
DISREGARDING: JAUNDICE, SKIN SPIDER ANGIOMATA, CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: AGE 26 TO 55, EXPOSURE TO RABBITS OR OTHER SMALL MAMMALS, SEX MALE, ANOREXIA, DIARRHEA ACUTE, MYALGIA, VOMITING RECENT, FEVER, LEG (S> WEAKNESS BILATERAL, LEG <S> WEAKNESS PROXIMAL ONLY, PRESSURE ARTERIAL ORTHOSTATIC HYPOTENSION, PRESSURE ARTERIAL SYSTOLIC 90 TO 110, TACHYCARDIA, WBC 14000 TO 30000, PLATELETS LESS THAN 50000
DISCRIMINATE: LEPTOSPIROSIS SYSTEMIC, SARCOIDOSIS CHRONIC SYSTEMIC
The effect of the negative responses concerning abdominal pain has been to lower the scores of all of the hepatic disorders considered in the previous differential diagnosis. This time, when the partitioning algorithm is invoked the highest ranking alternative is systemic leptospirosis: the only other diagnosis on the list capable of explaining substantially the same set of findings is systemic sarcoidosis. The keyword DISCRIMINATE indicates that the list of alternatives contains between two and four elements, the leading two of which are selected for comparative analysis. When engaged in a DISCRIMINATE mode of analysis the program will attempt to ask questions serving to support one diagnosis at the expense of the other; more costly procedures may be called for in order to achieve this objective.
Please Enter Findings of VOMITING/REGURGITATION *GO
HEMATEMESIS ? NO
HEMOPTYSIS GROSS ? NO
Please Enter Findings of TEMPERATURE *GO
RIGOR <S> ? YES
Please Enter Findings of NEUROLOGIC EXAM CRANIAL NERVE <S> *GO
NERVE PARALYSIS SEVENTH CRANIAL BILATERAL ? NO
SPLENECTOMY HX ? NO
The program is not actually interested in the answer to this question; what it wants to know is whether the spleen is enlarged. Because of the possibility of being misled by a negative answer, appropriate blocks have been created to prevent the program from asking about an increased spleen size in a patient whose spleen had been removed.
Please Enter Findings of PALPATION ABDOMEN *GO
SPLENOMEGALY MODERATE ? NO
Please Enter Findings of XRAY LUNG FIELD <S> *GO
CHEST XRAY HILAR ADENOPATHY BILATERAL ? NO
DISREGARDING: JAUNDICE, SKIN SPIDER ANGIOMATA, CREATINtNE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: AGE 26 TO 55, EXPOSURE TO RABBITS OR OTHER SMALL MAMMALS, SEX MALE, ANOREXIA, DIARRHEA ACUTE, MYALGIA, VOMITING RECENT, FEVER, LEG <S> WEAKNESS BILATERAL, LEG <S> WEAKNESS PROXIMAL ONLY, PRESSURE ARTERIAL ORTHOSTATIC HYPOTENSION, PRESSURE ARTERIAL SYSTOLIC 90 TO 110, RIGOR (S>, TACHYCARDIA, WBC 14000 TO 30000, PLATELETS LESS THAN 50000
PURSUING: LEPTOSPIROSIS SYSTEMIC
The question about rigors (shaking chills) is enough to separate the scores of these items so that now there is only one alternative left in the differential diagnosis. Before concluding that this diagnosis is actually correct, however, the program will now attempt to achieve a degree of separation between this diagnosis and its nearest competitor (now below the threshold and not printed out) that is twice the threshold value. The program invokes a PURSUING strategy, which calls for the identification and acquisition of clinching data: at this stage, the level of questioning is unconstrained so the program can ask about biopsies if useful, or other specialized procedures capable of providing pathognomonic data.
LEPTOSPIRA AGGLUTINATION POSITIVE ? YES
This finding is enough to clinch the diagnosis. However, the program proceeds to ask the additional questions that had been prepared for this round of information acquisition. As implemented in this program, the process of task formulation is too tame consuming to have the procedure recycle after each new datum is entered.
Please Enter Findings of BLOOD CULTURE *GO
BLOOD CULTURE LEPTOSPIRA ? N/A
Please Enter Findings of URINE CULTURE *GO
URINE CULTURE LEPTOSPIRA ? N/A
DISREGARDING: JAUNDICE, SKIN SPIDER ANGIOMATA, CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: AGE 26 TO 55, EXPOSURE TO RABBITS OR OTHER SMALL MAMMALS, SEX MALE, ANOREXIA, DIARRHEA ACUTE, MYALGIA, VOMITING RECENT, FEVER. LEG <S> WEAKNESS BILATERAL, LEG <S> WEAKNESS PROXIMAL ONLY, PRESSURE ARTERIAL ORTHOSTATIC HYPOTENSION, PRESSURE ARTERIAL SYSTOLIC 90 TO 110, RIGOR <S>, TACHYCARDIA, WBC 14000 TO 30000, LEPTOSPIRA AGGLUTINATION POSITIVE, PLATELETS LESS THAN 50000
PURSUING: LEPTOSPIROSIS SYSTEMIC CONCLUDE: LEPTOSPIROSIS SYSTEMIC
Having concluded leptospirosis, the program now deletes from further consideration those items explained by this diagnosis. If there are significant data remaining to be explained, the task formulation procedure is again invoked to determine the next most compelling differential diagnosis. In the scoring process, any diagnoses that are causally linked to the concluded disease are awarded an extra bonus. This enhances the likelihood of their being noticed by the task formulation, but does not guarantee that they will be considered.
DISREGARDING: CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: ALCOHOLISM CHRONIC HX, FECES LIGHT COLORED, JAUNDICE, LIVER ENLARGED SLIGHT, SKIN PALMAR ERYTHEMA, SKIN SPIDER ANGIOMATA
RULEOUT: MICRONODAL CIRRHOSIS <LAENNECS>, HEPATIC LEPTOSPIROSIS, FATTY LIVER SECONDARY, CIRRHOSIS SECONDARY TO CHOLESTATIC DISEASE, ALCOHOLIC HEPATITIS, MACRONODAL CIRRHOSIS <POSTNECROTIC>, DRUG HYPERSENSITIVITY CHOLESTATIC REACTION
As the signs of acute febrile illness have been accounted for by the conclusion of systemic leptospirosis. the diagnostic task formulated to deal with the liver involvement is now focused primarily on those chronic disorders that commonly cause the type of skin lesions reported in this patient. Note, however, that the possibility of hepatic involvement by leptospirosis--never mentioned in the earlier differential diagnoses dealing with the liver involvement--is now high on the list of alternatives.
LIVER EDGE HARD ? N/A
ONSET ABRUPT ? YES
JAUNDICE CHRONIC PERSISTENT HX ? NO
Please Enter Findings of INSPECTION HAND <S> AND FEET *GO
FINGER <S> CLUBBED ? NO
Please Enter Findings of INSPECTION AND PALPATION SKIN *GO
SKIN RASH MACULOPAPULAR ? NO
LIVER DISTORTED OR ASYMMETRICAL ? N/A
Please Enter Findings of INSPECTION AND PALPATION EXTREMITY <IES> *GO
LEG <S> EDEMA BILATERAL ? NO
ABDOMEN TENDERNESS GENERALIZED ? NO
ABDOMEN TENDERNESS RIGHT UPPER QUADRANT ? NO
DISREGARDING: SKIN SPIDER ANGIOMATA, CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: ONSET ABRUPT, FECES LIGHT COLORED, JAUNDICE, LIVER ENLARGED SLIGHT
DISCRIMINATE: HEPATIC LEPTOSPIROSIS, LARGE DUCT OBSTRUCTION
The abrupt onset of the illness tends to eliminate the chronic liver diseases from serious contention. However, the program does not yet have access to the results of liver function tests, which would help to discriminate between hepatocellular and cholestatic forms of acute involvement.
Please Enter Findings of TRANSAMINASE <S> *SGOT GTR THAN 400 *SGPT 200 TO 600 *GO
DISREGARDING: SKIN SPIDER ANGIOMATA, CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: FECES LIGHT COLORED, JAUNDICE, LIVER ENLARGED SLIGHT, SGOT GTR THAN 400, SGPT 200 TO 600
NARROW: HEPATIC LEPTOSPIROSIS, HEPATITIS ACUTE VIRAL
The term NARROW signifies that the task formulation procedure has constructed a broad differential list that would ordinarily suggest use of the RULEOUT strategy; however, as there are no helpful questions available without resorting to laboratory procedures, the field is arbitrarily restricted to the two leading contenders, and the DISCRIMINATE strategy is employed.
Please Enter Findings of BLOOD COUNT AND SMEAR *GO
WBC GTR THAN 30000 ? YES
Please Enter Findings of BLOOD PHOSPHATASE <S> *GO
ALKALINE PHOSPHATASE BLOOD GTR THAN 2 TIMES NORMAL ? YES
ABDOMEN PAIN EXACERBATION WITH MEAL <S> ? NO
ABDOMEN GUARDING INVOLUNTARY GENERALIZED ? NO
ABDOMEN GUARDING INVOLUNTARY LOCALIZED ? NO
Please Enter Findings of TRANSFUSION <S> HX *GO
TRANSFUSION <S> MULTIPLE HX 7 NO
DISREGARDING: SKIN SPIDER ANGIOMATA, CREATININE BLOOD INCREASED, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: FECES LIGHT COLORED, JAUNDICE, LIVER ENLARGED SLIGHT, ALKALINE PHOSPHATASE BLOOD GTR THAN 2 TIMES NORMAL, SGOT GTR THAN 400, WBC GTR THAN 30000, SGPT 200 TO 600
PURSUING: HEPATIC LEPTOSPIROSIS CONCLUDE: HEPATIC LEPTOSPIROSIS
DISREGARDING: SKIN SPIDER ANGIOMATA, UREA NITROGEN BLOOD 60 TO 100
CONSIDERING: OLIGURIA HX, CREATININE BLOOD INCREASED
RULEOUT: RENAL LEPTOSPIROSIS, GLOMERULONEPHRITIS ADVANCED CHRONIC, LEAD NEPHROPATHY, GLOMERULONEPHRITIS ACUTE, PYELONEPHRITIS CHRONIC, DIABETIC NEPHROPATHY
Having decided the nature of the hepatic involvement, INTERNIST-I now turns its attention to the differential diagnosis of renal disease in this patient. Although this problem was explored extensively by the program via a score or more additional questions. no conclusion was ever reached; the final statement of this differential at the time the program was interrupted appeared essentially as it does in this display.