vague symptoms
There are many diagnoses that do not have definitive tests used to determine them, or which can't be truly diagnosed until a patient has died (upon autopsy). In these cases, doctors must use combinations of symptoms, often vague symptoms, which can lead to a lack of diagnosis. The real medical problem may be highly unusual or not appropriate to the age of the patient. The doctor might not consider a diagnosis that is very rare, or very rare for that age of the patient.