I suspect, Nailit, that a doctor would use 'the Sherlock Holmes method'. i.e. he'd start with a list in his mind of every possible cause and then try to eliminate as many as possible.
For example, as he'd know that diabetes can lead to sensory neuropathy, he'd test your blood sugar level. If a normal result was found, he'd then be able to rule out diabetes.
He'd also ask you questions about your lifestyle, to see if that highlighted anything that he ought to be concentrating on. For example, if you told him that you were a heavy drinker he'd consider alcoholic neuropathy as a possible diagnosis and then carry out the tests listed here:
https://www.nlm.nih.gov/medlineplus/ency/article/000714.htm
(Many of the tests mentioned there might also be used to indicate, or rule out, other possible causes).