One of the wonderful functions of PDAs is the potential to have a program that produce a list of differential diagnoses for a given clinical feature(s). Developers realized this fact and created for us a number of DDx programs. For a list of these programs see this Pda4peds category.
You may also vote for your best differential diagnosis tool.
Such applications can be classified into:
1) single symptom lookup: i.e. the user enter a symptom, sign, lab result and will get a list of causes (differential diagnosis) for that symptom.
2) multiple symptoms analysis: i.e. the user enter multiple symptoms, signs, lab results and will get a list of differential diagnoses for that combination. This type can be further subclassified into:
2a) additive generators: the program will list all the diseases that may have symptom A and all the diseases that may have symptom B. Such a program will give the longest list of results and could not be very specific.
2b) subtractive generators: the program will list only the diseases that have both symptom A and B. Such a program will give highly specific results but may miss conditions if the database of clinical features is not big enough.
So The Ideal DDx Program would be;
1) Class 2b, with comprehensive database that include every possible clinical feature (no matter how rare it is) for every disease in the world.
2) Patient Specific, the program takes into account other patient’s parameter such as age, sex, ethnicity, location, and duration of symptoms and modifies the results accordingly. This is specially important for us pediatricians.
3) Arranged Results, the generated list is arranged from the most common to the rarest possibilty.
4) Interactive, asks the user further details in order to narrow the diagnosis see Epocrates Sx as an example.