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Medical reasoning

(This page was created for AAAI-11 student poster Medical Treatment Conflict Resolving in Answer Set Programming. Content may be outdated. )

AI research started from automated reasoning. Computers can help us on many medical issues, e.g., medical decision making. But not enough applications have been seen so far. I am interested in representing human knowledge to computers (e.g., retrived from the web and structurally organized) and let them help medical personnel in clinical practice (e.g., confirming decisions or suggesting causes/solutions).


Medical reasoning (reasoning over medical domain problems, such as making treatment decisions) can be a good application knowledge representation and automated reasoning for the following reasons:
1. Human brain is not good hangling large volume of information.
2. No one is perfect and hence we can make mistakes, especially under pressure.
3. A physician can only reason using the knowledge in his/her brain, but not knowledge known by others.
4. We always want the ``solution book.''

In contrast, computers have large memory and fast processing speed, and more important, the ability to collect and exchange volume information efficently. If we can implement an approach to easily represent the medical knowledge of many veteran physicans to the computer, it can help an unexperience physician to make decisions. It's like he/she is having a very ``smart'' and ``knowledgable'' assistant.

In building a reasoning system to solve a treatment conflicting problem, we have realized that how important non-monotonicity is for medical reasoning, and discovered the great expressive power of answer set programming, a non-monotoic logic programming paradigm. So we decide to study the non-monotonicity in medical reasoning and implement automated reasoning on certain problems that drive physicians nuts. We will also take a look at the application of ASP's extension, such as probablistic reasoning and (numeric) constraint solving, for reasoning over medical domain.


The medical information below is for computer science research only. It should NOT be used in any medical practice and/or as a reference, support or proof. Please consult professional medical personnel or formal medical publications. The authors hold NO responsibility for any consequence of using this information.

Non-monotonicity and Medical Reasoning

Reasoning for medical diagnosis has two interesting features. First, not all information is complete and change from time to time a lot. Sometimes the physician may know whether a patient is allergy to a medication. Sometimes, not. The reasoning system needs to be able to work correctly in both cases. We call this reasoning about knowledge. Second, medical knowledge has exceptions. Medication allergy is one kind of exceptions to the treatment of a symptom. But in most cases, physicians do according to some default procedures. Hence, the reasoning system needs to handle default reasoning.

The above two features requires non-monotonicity - when new information becomes available, the conclusion will be changed.

Let's take a look at an example, drug-based epilepsy treatment. Most epilepsy patients are treated using medication and can control epilepsy well in medication. But deciding the medication and the dose for each individual is an ``iterating'' process. The physician has to work with the patient closly to alternate the prescription over a long time. This is what you will see in chronological order:

1. The physician and the patient discuss a lot to determine whether medication is needed - if the seizure is rare and mild, maybe the physician will let you live with it.
2. The physician will prescribe patients a medication to see how things goes.
3. The anticonvulsant (i.e., anti-epilepsy, anti-seizure) level of patients needs to be monitored and doses of medications should be changed accordingly.
4. If the medication does not work well (one case is that after a very long time, e.g., 10 years, the medication cannot suppress seizures any more.), return to step 1 and try others.
5. The patient and the physician may think about stopping the medication after a long (e.g., five years) seizure-free period.
6. Return to step 1 if seizures restart again. A medication used to work for the patient may not work any more.

Each step above requires non-monotonicity.

User-friendly in Medical Reasoning

In the example above, much information (time-variant and patient-specified) needs to be entered by physicians to computers on field. This rises the ``user-friendly'' concern. The language/interface for physicians to pass information to computers has to be very simple, as close to natural language as possible. We do not want the physicians to struggle with semantics much.

Answer Set Programming: A Good Candidate

Satisfying all above concerns, A-prolog, the language for Answer Set Programming (ASP), is a good candidate. ASP has a large user base with industry input. The ASP community has combined ASP with CSP and CLP to support both boolean and numeric constraints, and extended ASP for probabilistic reasoning. Either numbers and probabilities (a special kind of numbers) are frequently used in medical domain.

ASP in resolving medical treatment conflict

One case that computer-aided medical reasoning can be useful is resolving treatment conflict. Conflicts (e.g., two medication can generate toxic chemicals while each of them treats one symptom on the patient) happen a lot in medical reasoning. In this case, we need to tell computers which symptom is the priority, i.e., symptom priority ranking. With this information, an alternative compromising treatment can be made by focusing on the priority.

We use a simple running example to introduce our idea. There are two symptoms. Hemoptysis (i.e., coughing up blood) can be relieved by increasing blood coagulation whereas hypertension (i.e., high blood pressure) can be relieved by decreasing blood coagulation. We have two medications, A and B, such that A increases blood coagulation whereas B decreases blood coagulation.

It is very easy to decide the treatment for either one of the two symptoms. But it becomes difficult when the patient suffers both, because the treatments to the two symptoms, i.e., increasing and decreasing blood coagulation, conflict with each other.

To resolve treatment conflict, physicians can prioritize symptoms (e.g., according to life-threatening level) on field. The symptom priority ranking tells that relieving which symptom is the priority for the patient. Though priority ranking of symptoms is not textbook knowledge, it is an important criterion for physicians to make decisions. In our example, if hemoptysis is a higher priority, then the physician will still prescribe medication $A$ but in half of its normal dose. Ranking symptom priority has been studied in medical community for a while.

We can then represent the knowledge (pure knowledge, without any information about patients) as follows:
* A patient's blood coagulation should be increased (decreased), if he/she is suffering hemoptysis (hypertension), unless it should not.
* The patient should take medication A (B), if his/her blood coagulation should be increased (decreased)
unless hemoptysis (hypertension) is a higher priority.
* Medications A and B cannot be taken at the same time.
* If a patient's blood coagulation should be increased (decrease) while being prescribed medication B (A), half the dose.

The knowledge above can be encoded into ASP as follows.

% knowledge 1-2/rules 1 and 2:
should(increase, X) :- hemoptysis(X), not -should(increase, X).
should(decrease, X) :- hypertension(X), not -should(decrease, X).

% knowledge 3-5/rules 3 and 4:
takes(X, a) :- should(increase, X), not takes(X, b), not -priority(hemoptysis, X).
takes(X, b) :- should(decrease, X), not takes(X, a), not -priority(hypertension, X).

% knowledge 6/rule 5: 
half_dose(X, a):- should(decrease, X), takes(X, a).

% knowledge 7/rule 6: 
half_dose(X, b) :- should(increase, X),  takes(X, b).

Now let's create a virtual patient, Tom, such that

priority(hemoptysis, tom).       % rule p1
-priority(hypertension, tom).    % rule p2

The answer set is


If we comment rules p1 and p2 (telling no priority information to the computer), an additional answer set pops up.


More ``killer'' applications of ASP in medical reasoning are coming.