The next steps: Differential diagnosis and initial management

Introduction

The term ‘Differential Diagnosis’ used to be very widely used by doctors, but it now seems to be used less, and is less well understood. It might be better termed as ‘Differential Diagnoses’, because the process of preparing it is to formulate a list of possible diagnoses that cover the presenting clinical situation, usually written in the descending order of likelihood. It is a very important part of the overall treatment of a patient from initial presentation, particularly in the emergency situation. Hopefully, the doctor clerking a patient will write a thorough history and complete a detailed examination. He may write a good plan of treatment, but the intermediate step of preparing the differential diagnoses is often missed or replaced by something which is entitled ‘Impression’, which often only considers one possibility. Box 3.1 gives three illustrations of situations in which the ‘Impression’ is too restrictive, whereas a full differential diagnosis would allow the treating doctors to consider the full range of possibilities, including those that are quite rare, but nevertheless vitally important if present.

One of the most common reasons for attendance at an Emergency Department with chest pain is because the patient himself or a referring doctor is worried that the chest pain is of cardiac origin. This is the reason a receiving doctor might write ‘chest pain, rule out cardiac cause’ as the overall ‘impression’. However, there are other causes of acute chest pain, both common and rare. There is often a feeling that suggesting rare diagnoses opens avenues of investigations that are time consuming and expensive, but this is far from the truth. For instance, it may take only brief consideration that the patient may have a dissecting thoracic aortic aneurysm to return to the patient and clarify the character of the chest pain (dissecting aneurysms produce pain that is tearing in nature and clearly going through from front to back) and to check the blood pressure in both arms. Together with a simple chest X-ray, this may be sufficient evidence to exclude a dissecting thoracic aortic aneurysm without the need to resort to an emergency computed tomography (CT) scan.

The most common cause of an acute headache is probably a tension headache. There is no useful test for this and the diagnosis will largely be made on history. Particularly in the emergency situation, some very serious causes of acute headache must not be missed, such as a subarachnoid haemorrhage or a sagittal sinus thrombosis. Careful and accurate differentiation between these two is clearly imperative because anticoagulation for a suspected sagittal sinus thrombosis would be completely the wrong treatment for a subarachnoid haemorrhage.

The process of differential diagnosis does not mean that every single possible cause needs to be specifically excluded in every clinical situation. However, having the full list of differential diagnoses written down helps the doctor weigh the likelihood of each one and then clarify the situation as is appropriate to the particular clinical situation. This clarification will not necessarily mean arranging complex investigations. It might mean just a mental check that the right specific questions have been asked or making sure that particular physical signs have been checked.

This reviewing, checking and clarification process that is mentally undertaken by the doctor clerking the patient is not something that needs to be delayed until the history and examination are completed. As the student and doctor become more experienced in the process of history and examination and the preparation of the differential diagnoses, they will begin to think through the patient’s problems as soon as the consultation begins. The consultation will often be punctuated by key questions aimed at confirming or refuting a particular diagnosis that has occurred to the doctor during the course of the clerking process. Box 3.2 is a list of some key questions and the diagnoses to which they refer.

Management plan

Having obtained the history and examination details and formulated a list of differential diagnoses, the student or doctor needs to decide on what should happen next. As with everything clinical, what the patient actually wants is of paramount importance. Box 1.16 in Chapter 1 gives a list of the general scenarios that may lie behind a consultation between patient and doctor. Of particular relevance to the process of differential diagnosis and planning management is the degree to which patients want answers to queries or relief of symptoms. Quite a useful question can be ‘Are you worried about your symptoms because of the trouble they give you and you want to be rid of them, because of what might be wrong, or both?’ This can be quite a confusing question for the patient, but if explained carefully and answered specifically, it can avoid a lot of unnecessary investigation. In addition, starting out on the right track can make subsequent management much simpler, and it is often much easier to reassure patients that nothing is seriously wrong than to give them an exact diagnosis or full relief of symptoms. This process particularly applies to a patient who has a fear of cancer. In a relatively young patient with quite harmless symptoms, even if a serious diagnosis is not really suspected, it may be necessary to perform some sort of investigation (such as an endoscopy or a CT/magnetic resonance image scan) to provide the necessary reassurance, even if it is not absolutely necessary for the process of resolving the differential diagnosis.

The priority of different investigations, the order in which they are done and the question of when treatment is given, all have to be considered and planned carefully. There is often quite a strong temptation for the doctor making the initial plan to start off with quite a large series of investigations. This is often done because the doctor assumes the patient needs the reassurance of normal tests and, to some extent, doctors need that reassurance themselves. There may even be a temptation to practice defensive medicine to avoid being accused in the future of under-investigating and missing diagnoses. However, this level of investigation is often not a productive way forward; it can overuse resources, sometimes prevent other patients having their tests in a timely manner, and, according to circumstance, can be financially detrimental to the individual patient. However, there may also be drawbacks to a logical series investigation and planning the next test only when the results of the first one are known. On occasions, this can seem a slow and tedious process for the patient, particularly if the health system allows only relatively infrequent patient review. Box 3.3 illustrates some clinical scenarios and the contrast in investigation style.