Differential diagnosis

# Overview
In medicine, differential diagnosis (sometimes abbreviated DDx or ) is the systematic method physicians use to identify the disease causing a patient's symptoms.
Before a medical condition can be treated, it must be identified.  In the process of listening to a patient's complaints, examining the patient, and taking the patient's personal, family and social history, the physician makes a mental list of the most likely causes. The doctor asks additional questions and performs tests to eliminate possibilities until he or she is satisfied that the single most likely cause has been identified.
Once a working diagnosis is reached, the physician prescribes a therapy. If the patient's condition does not improve, the diagnosis must be reassessed.  The method of differential diagnosis was first suggested for use in the diagnosis of mental disorders by Emil Kraepelin. It is more systematic than the old-fashioned method of diagnosis by gestalt (impression).
The term differential diagnosis also refers to medical information specially organized to aid in diagnosis, particularly a list of the most common causes of a given symptom, annotated with advice on how to narrow down the list.

# Tactics
There are various methods of clinical reasoning include probabilistic (Bayesian), causal (physiologic), and deterministic (rule-based).  In addition, medical experts rely more on pattern recognition which is faster; however, clinical experts seem flexible and may use whichever method of reasoning most easily represents and solves a given problem. When confronted with non-challenging cases physicians may use 'nonanalytical reasoning' such as pattern recognition; however, during more difficult cases physicians may switch to 'reflective reasoning'. Reflective reasoning may especially help complex cases. Explicit Bayesian thinking with precise numbers is rarely done. Basic science knowledge is probably "encapsulated" into clinical knowledge.
Possible strategies to improve clinical reasoning have been reviewed and using problem-based learning, include teaching appropriate problem representation creating a one-sentence summary of a case, standardized patients, teaching hypothetico-deductive reasoning, cognitive forcing strategies to avoid premature closure, teaching the competing-hypotheses heuristic, using fuzzy-trace theory and mixed-methods interventions. Studies are unclear about  teaching logic.
Scales to measure clinical reasoning have been proposed.

## Hypothetico-deductive reasoning
Regarding hypothetico-deductive reasoning, an observational study on the methods used by experts solving clinicopathological exercises reported that these experts use the following six steps:
- aggregation of groups of findings into patterns
- selection of a "pivot" or key finding
- generation of a cause list
- pruning of the cause list
- selection of a diagnosis
- validation of the diagnosis

## Mnemonics
For the differential diagnosis of systemic disorders, the mnemonic VINDICATE or VITAMINSABCEDK may help prompt considerations.

## Deliberate practice with cases and simulations
Deliberate practice with cases and simulations maybe helpful.

## Problem representation
Successfully distilling complex information into a short summary, perhaps using semantic qualifiers, may help diagnostic accuracy. Problem representation, "usually as a one-sentence summary defining the specific case in abstract terms," may help clinical reasoning.

## Numeracy
Various methods have been proposed for improving quantitative literacy. For diagnosis, likelihood ratios or sensitivity and specificity are two methods. It is unclear which method is better according to the results of a controlled trial.
Studies are inconclusive on using cognitive feedback..
Framing bias is best avoided by using numeracy with absolute measures of efficacy.