Medical malpractice cases involve requirements including proof of an established provider-patient relationship, that the healthcare provider failed to meet the standards of care, and that the error caused significant damages.
Specifically for a misdiagnosis case, you also need to provide proof of the following to move forward with a case:
That the illness or injury would not have been misdiagnosed by another doctor or healthcare provider with the same or similar specialty.
That a competent provider would have designated the correct diagnosis when determining possibilities for the injury or illness, but the current provider did not.
If the provider gave the correct diagnosis, then you need to prove that they did not perform the right tests to arrive at the diagnosis.