Differential diagnosis

In healthcare, a differential diagnosis or nomothetic(DDx) or is a way to find out which disease or condition a patient has when several illnesses show similar symptoms. Doctors use this method to figure out the exact illness or to check for any serious, life-threatening problems. Each possible illness is called a differential diagnosis. For example, if a patient has a cough, acute bronchitis might be one possible diagnosis, even if the final diagnosis is a common cold.

Differential diagnosis is a step-by-step process used to identify the correct disease when many possibilities exist. This process is like elimination, where doctors gather information from symptoms, patient history, and medical knowledge to rule out unlikely diseases until they find the most probable one. This method is similar to the hypothetico-deductive approach, where doctors think of possible diseases as hypotheses and test whether they are true or false.

In psychiatry, differential diagnosis is also important because some mental health conditions have overlapping symptoms. For example, a patient diagnosed with bipolar disorder might also be considered for other diagnoses like attention deficit hyperactivity disorder (ADHD), major depressive disorder, post-traumatic stress disorder (PTSD), anxiety disorders, or borderline personality disorder.

How doctors prepare a list of possible diagnoses depends on their experience. New doctors may carefully check all possible causes, while experienced doctors often use their knowledge and pattern recognition to avoid unnecessary delays, risks, and costs. Good doctors combine their experience with evidence from medical research to make the best decisions.