In most instances the diagnosis is apparent. In the general practice setting almost 90% of diagnoses are established at the completion of the history and examination [1]. In one outpatient clinic this figure was 73% (history 56% and examination 17%) in patients with cardiovascular, neurological, respiratory, urinary and other miscellaneous problems [2]. In patients with neurological problems the initial diagnosis is less obvious and was correct in only 60% of patients presenting to an emergency department [3]. In this setting the appropriate course of action is to initiate investigations that can confirm the diagnosis, exclude alternative diagnoses with potentially more severe adverse outcomes and institute a plan of management taking into account factors in the past, social and medical drug history that would influence management in this particular patient.

A word of caution: being absolutely certain is potentially the most dangerous scenario. Doctors are strongly anchored by their initial diagnoses [4] (see Case 6.1) and are at risk of closing their minds to possible alternatives, often in the presence of clinical features or results from investigations that should raise doubt about the diagnosis.

CASE 6.1 An incorrect initial diagnosis

An example is a 65-year-old patient with confusion and headache who was treated for herpes zoster (HZV) meningoencephalitis because the CSF contained HZV DNA. The CSF findings of a very high white cell count and protein level and very low glucose level were most atypical for HZV meningoencephalitis. In addition, the patient was failing to respond to the appropriate treatment for HZV. The positive test for DNA related to the presence of herpes zoster ophthalmicus [5]. The patient had malignant meningitis.

Doctors recognise patterns of familiar problems with respect to critical cues [6]. Doctors who are more experienced appear to weigh their first impressions more heavily than those who are less experienced and at risk of closing their minds early on in the diagnostic process [7]. Even experienced clinicians may be unaware of the correctness of their diagnoses when they initially make them [8].

If there are tests to confirm the diagnosis, it is appropriate to perform those tests, provided the patient is informed of the risks associated with them. When ordering tests and reviewing the results, it is most important to be aware of the sensitivity and specificity and the influence of the prevalence of the disease on the positive predictive value and the negative predictive value of those tests [9] (for a discussion of these concepts, refer to the section ‘Understanding and interpreting test results’ below).

If there are no tests, one can proceed cautiously with management, but it is most important to review the response to therapy. A lack of response to therapy or the emergence of unexpected side effects (the latter is a personal observation) is often a clue that the diagnosis is incorrect. Conversely, a response to a therapy does not prove the diagnosis. This author has seen patients with vertebral artery dissection, viral meningitis and pituitary cysts ‘respond’ to treatment for migraine. This is discussed in more detail below.

There are several possible diagnoses

It is imperative to keep the diagnostic options open by making provisional diagnoses while keeping alternatives in mind. Be circumspect and take action to minimise the possibility of missing other critical diagnoses [10]. Once again, if there are tests that can differentiate one particular diagnosis from another, it would be most appropriate to perform those tests. If a specific diagnosis cannot be made following the investigations, the approach is similar to that discussed in the following section.

You have no idea what is wrong

In the setting of uncertainty there are several possible courses of action. A particularly useful strategy is to start again: take a more detailed history and repeat the examination.¹ This is the approach recommended when you have absolutely no idea what the diagnosis is. In this situation performing many tests is often misleading because of the sensitivity and specificity of tests.

If you have elicited a detailed history, but still have no idea what is wrong with the patient, there are several options including:

• wait and see

• perform investigations

• seek a second opinion

• consult a textbook

• search for an answer on the Internet.

These various approaches will be discussed in terms of their relative merits and deficiencies.

WAIT AND SEE

In resolving uncertainty, time is a very powerful diagnostic tool. The idea is to wait for a period of time in the hope that the diagnosis becomes clear or the patient gets better [10], [11]. The effective use of this approach requires considerable skill, however. Often in this situation a doctor may order unnecessary tests in the hope that a diagnosis may be established; most often it is not. If the ‘wait and see’ approach is adopted, it is important to:

• inform the patient that there is uncertainty

• advise them of the possible outcomes

• recommend that they report immediately should symptoms worsen or if any new symptoms develop.

Shared medical decision making is a process in which patients and providers consider outcome probabilities and patient preferences and reach a healthcare decision based on mutual agreement. Shared decision making is best employed for problems involving medical uncertainty [12]. However, it is important to consider the fact that not all patients wish to be involved in shared medical decisions [13].

UNDERTAKE INVESTIGATIONS

In most cases there are tests that can confirm or exclude a particular disease. In this situation it is important to understand the concepts of the sensitivity and specificity of tests and the importance of prevalence of the disease. The essential questions to ask when considering investigations include:

• In what way will the results, whether positive or negative, alter the management of this patient?

• What is the risk of undertaking the test?

There is a more detailed discussion of investigations later in this chapter.

There are no tests for some diseases and the diagnosis is based entirely on the clinical features. When there are several possible diagnoses or when one has absolutely no idea what the diagnosis might be, performing numerous tests in the hope of making a diagnosis is a wonderful way of giving the illusion that something useful is being done when often all that may be achieved is stalling or buying time. It is a tactic that is used by a number of clinicians in the hope that a diagnosis will be made by a test result (unlikely), the illness will progress so that the diagnosis will become apparent or the patient’s problem will resolve. A reasonable approach is to think of the worst case scenario (the most serious diagnosis that the symptoms could represent, a diagnosis that if missed could result in an adverse outcome) and proceed accordingly.

OBTAIN A SECOND OPINION

Although doctors prefer to obtain information from journals and books, they often consult colleagues to get answers to clinical and research questions [14], [15]. Even for doctors whose first choice of information source was the medical literature – either books or journals – the most frequent second choice was consultations [14].

In a study of 254 referrals seen by a neurologist there was a significant change in diagnosis in 55%, and in management in nearly 70% [16].

There are several ways of obtaining a second opinion:

• the ‘informal consultation with a colleague’

• telephone advice

• the ‘curbside’ conversation in the corridor without actually seeing the patient

• presenting at meetings and seeking several opinions, often but not invariably with the patient at the meeting

• the ‘formal second opinion’ when a colleague is asked to see the patient.

Telephone advice: Telephoning a colleague for advice is common. The recipient of the call is in a very difficult situation as providing the correct advice very much depends on being given the correct history and examination findings. An experienced clinician often knows the particular questions to ask and can decide if and when they should actually see the patient. It is probably wiser for an inexperienced clinician to arrange to formally see the patient in consultation.

Corridor or curbside consultation: ‘Corridor or curbside consultation’ is another approach used often [17]. Unfortunately, and sometimes with dire consequences, this is used by medical practitioners to seek informal advice about their own medical problems. The model of a good curbside consultation ‘is to say what you know and what you don’t know. Then you hope the person you are consulting with will treat you with respect’ [17]. Requesting doctors who could not present relevant information, frame a clear question or answer consultant questions in a well-informed manner were generally asked to formally refer the patient [17]. Perley et al [17] commented that tacit rules govern curbside consultation interactions, and negative consequences result when the rules are misunderstood or not observed.

Once again, the correct advice very much depends on being given the correct information. The neurologist providing advice will want to know the mode of onset and progression of the symptoms of the current illness together with the EXACT nature and distribution of the symptoms and the abnormal neurological signs, if present. It is difficult for inexperienced clinicians to perform detailed neurological examinations but there should be no reason why, as outlined in Chapter 2, ‘The neurological history’, an inexperienced clinician cannot obtain a detailed history. Finally, the neurologist would want information about the social, past and drug history that may influence any subsequent course of action.

Clinical meetings: Second opinions are often sought for the purpose of diagnosis and/or treatment in clinical meetings. There is the perception that one is obtaining multiple opinions. Although this can be a valuable tool, particularly if one of the participants identifies the problem, in a more complex case often what is said in meetings is very different to what is said in a formal consultation. Thus, the advice obtained in clinical meetings should be viewed circumspectly. A brain biopsy is often recommended in clinical meetings, but not often performed despite the recommendation.²

The formal second opinion: The formal second opinion is probably the most effective method of dealing with diagnostic or therapeutic uncertainties. There is no shame in asking a colleague to formally see the patient for a second opinion. If you do, it can be a learning experience; if you do not and the patient perceives a lack of progress, they will independently seek a second opinion and you will miss out on a learning opportunity. If a patient requests a second opinion, NEVER hesitate to arrange one.

Remember a second opinion is simply that; you are the clinician caring for the patient and the ‘buck stops with you’. You must decide if the second opinion is useful or not and act accordingly – this may include obtaining a third opinion!

CONSULT A TEXTBOOK

Yet another approach is to consult textbooks. This is useful if you are looking at the clinical features of a particular disease(s) or to learn what investigations would be appropriate. However, therapy is evolving so rapidly that recommended therapy in textbooks is soon out of date.

SEARCH THE INTERNET

An increasingly popular and useful strategy is to search the Internet ³ [18–20]. Patients frequently look for answers on the internet [21]. In the author’s own experience many patients bring the results of their searches to the consultation. In one study [19] Google was able to make the correct diagnosis in 58% of the cases in the New England Journal of Medicine

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