The idea of using computers to aid in medical diagnosis is older than you are, probably older than you and me put together. The field is called Medical Decision Support (MDS). The Department of Defense invested heavily in MDS, and last I knew, MDS was a key component in Armed Forces Health Longitudinal Technology Application.
Medical knowledge is collated by accomplished medical specialists, often surgeons and/or professors. The knowledge is weighted and encoded into modules using a specialized computer language. An engine runs a given module based on initial questions, then drops or engages modules based on how the questions/answers progress. Various tests are performed along the way, e.g. Bakody Sign for a cervical radiculopathy. At the end, the software spits out something like:
- 5/5 indications for C4/C5 nerve impingement
- 1/8 indications for COPD
- 8/10 indications for douchebaggery
- suggest the [X, Y, Z] for further testing
The same company (PKC) that first developed MDS was founded by the guy who also developed the Problem-Oriented Medical Record, an early form of EMR and an efficient means to quantify medical diagnoses. I worked for him at PKC and wrote the IIS version of the engine. You can see a deeply neutered version of the software at Sharecare (I think they now call it AskMD).