When residents of the Chicago area go to their doctors, they expect that the doctor will promptly inform them of what is wrong and will start a proper course of treatment. When a doctor misses a diagnosis or gets a diagnosis wrong, it can at best be an inconvenience to the patient and, at worst, cause the patient serious medical problems that can even lead to death.
However, a missed diagnosis is not always a case of medical malpractice. To some extent, the practice of medicine remains an art, and it is therefore hard for a doctor to get a diagnosis right all of the time, particularly since many different conditions manifest themselves with the same symptoms.
Generally speaking, if a doctor follows the correct procedure for making a difficult diagnosis, then he or she will not be legally responsible if it turns out that this or her best guess was wrong. Generally speaking, a doctor is expected to make a "differential diagnosis" after assessing his or her patient. What this means is that the doctor should create a list, in order of likelihood, of all the medical conditions that could be ailing the patient.
The doctor then goes down the list, performing tests to either confirm or rule out each possible diagnosis until the doctor feels comfortable starting treatment. So long as the doctor follows this process, he or she has met the standard of care.
However, if a doctor did not even consider a possible diagnosis that turned out to be correct, then the patient may be able to sue for medical malpractice. Likewise, if a doctor has a condition on his or her list but does not do enough to rule out or confirm that condition, a patient may be able to sue if it turns out the doctor overlooked the correct diagnosis.