Differential Diagnosis: Definition, History, Specific Methods, Help of Artificial Intelligence and Uses Outside of Medicine

In medicine, it refers to the distinction of a disease or condition particular to others that have similar clinical characteristics.

Physicians and other trained medical professionals use differential diagnostic procedures to diagnose the specific disease in a patient or, at least, to eliminate any imminent, life-threatening condition.

Frequently, each individual option of a possible disease is called a differential diagnosis (for example, acute bronchitis could be a differential diagnosis in the evaluation of a cough that ends with a final diagnosis of the common cold).

More generally, a differential diagnostic procedure is a method of systematic diagnosis used to identify the presence of a disease entity in which multiple alternatives are possible.

This method is essentially a process of elimination or at least a process of obtaining information that reduces the “probabilities” of the conditions of the candidate to insignificant levels.

Through the use of evidence such as symptoms, patient history and medical knowledge to adjust epistemic confidences in the mind of the diagnostician (or, for computer-assisted or computer-aided diagnosis, the system software).

The differential diagnosis can be considered as the implementation of aspects of the hypothetico-deductive method, in the sense that the potential presence of diseases or candidate conditions can be seen as hypotheses that doctors also determine as true or false.

Common abbreviations of the term “differential diagnosis” include DDx, ddx, DD, D / Dx, ΔΔ or ΔΔχ.

General components

A differential diagnosis of standard care has four steps. Patient safety requires that the doctor:

  • Gather all the information about the patient and create a list of symptoms. The list can be written in the mind or memory of the doctor, as long as a list is made.
  • List all possible causes (candidate conditions) for the symptoms. Again, this can be written mentally by the doctor, but it should be done.
  • Prioritize the list by placing the most urgent possible causes at the top of the list.
  • Discard or treat the possible causes, starting with the most urgent condition and working the rest of the list. Discarding practically means testing and other scientific methods to determine that a condition has a clinically insignificant probability of being the cause.

If there is no diagnosis, it means that the doctor made an error or that the condition is not documented. The doctor eliminates the diagnoses from the list by observing and applying tests that produce different results, depending on the diagnosis that is correct.


Diagnosis is the identification of the nature and cause of a certain phenomenon. The diagnosis is used in many different disciplines with variations in the use of logic, analysis and experience to determine “cause and effect”.

In systems and computer engineering, it is generally used to determine the causes of symptoms, mitigations and solutions.

Specific methods

There are several methods for differential diagnostic procedures and several variants among them.

In addition, a differential diagnostic procedure can be used concomitantly or alternatively with protocols, guides or other diagnostic procedures (such as pattern recognition or the use of medical algorithms).

For example, in case of a medical emergency, there may not be enough time to make detailed calculations or estimates of different probabilities, in which case the VRC protocol (airway, breathing and circulation) may be more appropriate.

Later, when the situation is less acute, a more complete differential diagnostic procedure can be adopted.

The differential diagnosis procedure can be simplified if a “pathognomonic” sign or symptom is found (in which case it is almost certain that the objective condition is present) or in the absence of a sine qua non sign or symptom (in which case it is almost certainly that the objective condition is absent).

A diagnostician can be selective, first considering those disorders that are more likely (a probabilistic approach), more serious if they are not diagnosed and not treated (a prognostic approach) or more receptive to treatment if offered (a pragmatic approach).

Since the subjective probability of the presence of a condition is never exactly 100% or 0%, the differential diagnostic procedure may aim to specify these various probabilities to form indications for further action.

The following are two methods of differential diagnosis, which are based on epidemiology and likelihood ratios, respectively.

Method based on epidemiology

One method to perform a differential diagnosis by epidemiology is to estimate the probability of each candidate condition by comparing its probabilities of having occurred in the first place in the individual.

It is based on probabilities related to both presentation (as well as pain) and the probabilities of the candidate’s various conditions (such as illness).

Coverage of candidate conditions

The validity of both the initial estimate of probabilities by epidemiology and the likelihood analysis depends on the inclusion of candidate conditions that are responsible for most of the likelihood of developing the condition, and it is clinically important to include them.

Where the relatively rapid onset of therapy is most likely to result in the greatest benefit.

If an important candidate condition is forgotten, no differential diagnostic method will provide the correct conclusion.

The need to find more candidate conditions for inclusion increases with the increase in the severity of the presentation itself.

For example, if the single presentation is a deviant laboratory parameter and all common harmful underlying conditions have been ruled out, then it may be acceptable to stop finding more candidate conditions, but this would be much more likely to be unacceptable if the presentation had been serious pain.


If two conditions obtain high probabilities after the test, especially if the sum of the probabilities for conditions with known probability ratios becomes greater than 100%, then the actual condition is a combination of both.

In such cases, that combined condition can be added to the list of candidate conditions, and the calculations should start from the beginning.

Using an initial method of epidemiology, the incidence of parathyroid carcinoma is estimated at approximately 1 in 6 million people per year, which gives a very low probability before taking any test under consideration.

In comparison, the likelihood that a non-malignant primary hyperparathyroidismoccurred at the same time as an unrelated noncarcinogenic cancer that occurs with malignant cells in the parathyroid gland is calculated by multiplying the probabilities of the two.

The resulting probability is, however, much less than 1 in 6 million. Therefore, the probability of parathyroid carcinoma can be close to 100% after histopathological examination despite the low probability that it will occur in the first place.

Finally, let’s say that the diagnosis of parathyroid carcinoma gave rise to a prolonged surgery that eliminated the remaining malignant tissue before it had metastasized, and the patient lived happily ever after.

Differential diagnosis by artificial intelligence

The machine differential diagnosis is the use of software to perform a total or partial differential diagnosis. It can be considered as an artificial intelligence application.

Many studies show an improvement in the quality of care and the reduction of medical errors through the use of such decision support systems.

Some of these systems are designed for a specific medical problem, such as schizophrenia , Lyme disease or pneumonia .

Others, such as ESAGIL, Iliad, QMR, DiagnosisPro, VisualDx, ZeroMD, DxMate, Symptoma and Physician Cognition are designed to cover all the main clinical and diagnostic findings to help physicians with a faster and more accurate diagnosis.

However, all these tools still require advanced medical skills to qualify the symptoms and choose additional tests to deduce the probabilities of different diagnoses.

Therefore, non-professionals should still see a health care provider for an adequate diagnosis.


The differential diagnosis method was first suggested for use in the diagnosis of mental disorders by Emil Kraepelin . It is more systematic than the outdated method of diagnosis by Gestalt therapy.

Alternative medical meanings

The “differential diagnosis” is also used more loosely, to refer simply to a list of the most common causes of a given symptom, to a list of disorders similar to a given disorder.

These lists when annotated with advice on how to reduce the list (the book ” Differential diagnosis index of France “, ISBN 0-340-81047-5, is an example). Therefore, a differential diagnosis in this sense is medical information specially organized to aid in the diagnosis.

Uses outside of medicine

Biological taxonomists also use methods similar to those of differential diagnostic processes in medicine to identify and classify living and extinct organisms.

For example, after finding an unknown species, first there may be a list of all potential species, followed by discarding one by one until, optimally, only one potential option remains.

Similar procedures can be used by plant and maintenance engineers, automotive mechanics, and used to diagnose defective electronic circuits.