User's Guide To Digital DDx

Digital DDx is an educational tool for medical students, residents, practicing clinicians and other health care professionals. It is not designed to provide medical advice for the lay public or to be used in the place of input from trained clinicians. 

How to use this app:

    Based on the history and exam findings obtained from the patient, a clinician can employ this app to generate a differential diagnosis (DDx).

    The opening screen is arranged by organ systems. Clicking on any system will reveal a list of common symptoms. For example, clicking on ‘Pulmonary’ opens a window with a list of symptoms that are frequently linked to pulmonary conditions (e.g. ‘Shortness of Breath?,’ ‘Cough?,’ ‘Hemoptysis?,’ etc.). Clicking on any of these symptoms takes the user through an organized cascade of conditions (e.g. ‘Pleural disorders’), ultimately leading to a list of possible diagnoses (e.g. ‘Pneumothorax’ or ‘Pleural effusion’).

    Each diagnosis contains specific information about the etiology, risk factors, symptoms and physical exam findings associated with that disease. This is presented in an easy to read format, which clearly describes the core features (i.e. an illness script) for each diagnosis, enabling the user to quickly determine how well it matches up with the patient in front of them. Some diagnoses include common testing done to rule in/rule out that disorder.

    Symptoms (e.g. fatigue), conditions (e.g. anemia) and diagnoses (e.g. iron deficiency) are further organized into functional frameworks. The frameworks chosen are based on what makes most sense for that condition or symptom. Examples of frameworks used include:
    1. Organ based: The symptom ‘Chest pain’ is divided into the following main organ system categories: Cardiac, Pulmonary, Gastrointestinal, MSK, Other. Each of these categories is then further broken down based on anatomic structure. For example, cardiac causes of chest pain include disorders affecting the coronary arteries, pericardium, myocardium and aorta.
    2. Anatomic: The symptom ‘Epigastric pain’ is divided into: Stomach/Esophagus, Pancreatic, Hepato-Biliary, and Non-GI categories. Each of these is further broken down by pathophysiologic process. For example, ‘Pancreatic’ is divided into the sub-categories: pancreatitis, pancreatic cancer, and pancreatic pseudocyst.
    3. Physiologic: The condition ‘Renal dysfunction’ is broken into ‘Pre-renal,’ ‘Intrinsic renal’ and ‘Post-renal’ causes. And ‘Intrinsic renal’ is further divided into disorders based on histologic structures within the kidney: glomerulous, interstitium, tubules, and vasculature.
    4. Additional frameworks used include: acute v chronic, painful v painless, and a few other selected schema.

    The ‘Search’ box allows the user to type in key words, enabling them to quickly find information about specific conditions, symptoms and diagnoses.

    Digital DDx can also be used as a Review of Symptoms guide. Working from the Organ system screen, commonly used questions (e.g. ‘Shortness of breath?’) for each system are provided, with diagnoses to consider provided for any positive response.

    Digital DDx is also a clinical study tool, enabling the learner to quickly review key symptoms within an organ system, as well as the most commonly associated diagnoses. It’s great for teaching conferences, morning report or case based learning, allowing the user to quickly access information in the moment in order to answer questions.

    The display path(s) field is visible on all pages (bottom of the screen), excluding the main page. It's an expandable/retractable button that displays all the paths that lead to a specific condition or diagnosis. This allows you to see the many ways of reaching that point, informing you about how a clinical problem may present. It also provides links to each element along the path.

    A few major organ system categories (e.g. Infectious Diseases) are arranged by organism and the organs that they infect (as opposed to symptoms or conditions). In a few other sections, conditions (e.g. anemia, vasculitis) are presented along with the core symptoms for a specific organ system.

    Links to images of findings and exam maneuvers associated with specific diagnoses are often available in the ‘links section’ of a condition or diagnosis. The user can use this feature to quickly access a picture of a disorder or remind themselves about how to perform an aspect of the exam. Links to selected sites for additional information are frequently available.

    Navigating through the app can be done quickly by scrolling and clicking - no typing is required. Clicking on the ‘Digital DDx’ logo (upper left corner) takes you back to the home screen.

    All of the information presented has been arranged based on the input of expert clinicians and is fully referenced (see reference page for details).

    To determine whether a diagnosis is likely, the user will generally need to further define the symptoms via additional questioning.

    Note that clinical presentations can be atypical and not follow the patterns described in this app. In addition, patients may suffer from more than one condition and sorting out which symptoms belong to which process can be challenging. Certain populations (e.g. very old, very young), disorders (e.g. immune-compromised), and other chronic conditions (e.g. sensory impairment) tend to cause atypical symptoms or other features not seen in normal hosts.

    Certain disorders have predilections for particular areas of the world, in particular infectious diseases. Differentials may therefore need to be adjusted to reflect local epidemiology.

    Finally, Digital DDx is biased towards the more commonly occurring disorders.

Key to abbreviations used in Digital DDx:
AKI = acute kidney injury, ASD= atrial septal defect, ASX= asymptomatic, AVM = arterial venous malformation, B = bilateral, BMI = body mass index, BRB = bright red blood, C = chills, CAP = community acquired pneumonia, CBD = common bile duct, CD = Crohn’s disease, CHF = congestive heart failure, CNS = central nervous system, COPD = chronic obstructive pulmonary disease, CKD = chronic kidney disease, CP = chest pain, CV= cardiovascular, CVAT = costo-vertebral angle tenderness, D = diarrhea, D/C = discharge, DM = diabetes, D/O = disorder, DOE = dyspnea on exertion, DVT= deep vein thrombosis, Dysfxn = dysfunction, DZ= disease, ED = erectile dysfunction, ET = essential thrombocytosis, ETOH = alcohol, ESRD = end stage renal disease, F = fever, FB = foreign body, FX= fracture, FXN = function, GI = gastrointestinal, GU = genitourinary, GYN= gynecologic, HA = headache, HD = hemodialysis, HF = heart failure, HFpEF = heart failure with preserved ejection fraction, HFrEF = heart failure with reduced ejection fraction, HPV = human papilloma virus; HTN = hypertension, HSV = herpes simplex virus, HX= history, IBD = inflammatory bowel disease, INFXN = infection, IVC = inferior vena cava, IV = intravenous, IVDU = intravenous drug use, LBP = low back pain, LN = lymph node, LOC = loss of consciousness, LVEDP = left ventricular end diastolic pressure, LMN = lower motor neuron, MI = myocardial infarction, N = nausea, NH = nursing home, NMJ = neuro-muscular junction, NSTEMI = non-st elevation mi, OSA = obstructive sleep apnea, PAD = peripheral arterial disease, PE = physical exam finding, PE = pulmonary embolism, PNS = peripheral nervous system, PVD = peripheral vascular disease, RF = risk factor, SOB = shortness of breath, RX = treatment, S = sweats, SBO = small bowel obstruction, STEMI = st-elevation mi, STI = sexually transmitted infection, SVT = supraventricular tachycardia, S = sweats, SX = symptom, UC = ulcerative colitis, UNSA = unstable angina, TOA= tubo-ovarian abscess, UMN = upper motor neuron, URI = upper respiratory tract infection, UTI = urinary tract infection, V = vomiting, VF = ventricular fibrillation, VSD = ventricular septal defect, VT = ventricular tachycardia, VZV = varicella zoster virus, WT= weight.

Contact Us/Send Feedback If you have any comments/suggestions please email us at This app is designed for educational and informational purposes only. Please do not email with clinical questions or with requests for medical advice. Charlie Goldberg MD and Derek Juang MD, University of California San Diego School of Medicine