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The use of the diagnostic model requires a disciplined approach to the problem with the medical practitioner quickly answering five self-posed questions (Table A1).
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1 The probability diagnosis This is based on the doctor’s perspective and experience of prevalence, incidence and the natural history of disease. The question is ‘for this particular patient with this specific problem/s presenting today, what is the likely diagnosis?’
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2 What serious disorders must not be missed? To achieve early recognition of serious illness the GP needs to develop a ‘high index of suspicion’. This is generally regarded as largely intuitive but is probably not so—it would be more accurate to say that it comes with experience. The serious disorders that should always be considered ‘until proven otherwise’ are listed in Table A2 and can be classified as V—vascular, I—infection (severe) and N—neoplasia, esp. cancer.
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Myocardial infarction, or ischaemia, is extremely important to consider as it is so potentially lethal and at times can be overlooked by the busy practitioner. Coronary artery disease may also manifest as life-threatening arrhythmias, which may present as palpitations and/or dizziness. A high index of suspicion is necessary to diagnose arrhythmias.
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The concept of red flags or ‘alarm bells’ is useful in this context, e.g.:
age >50
sudden onset of problem
history of cancer
fever >37.8°C
weight loss
pallor
overseas travel
unusual vomiting
neurological deficit
altered cognition/consciousness
failure to improve
syncope at toilet
drug or alcohol abuse
medication, e.g. steroids, biologicals
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3 What conditions are often missed? This question refers to the common ‘pitfalls’ so often encountered in general practice. This area is definitely related to the experience factor and includes rather simple non-life-threatening problems that can be so easily overlooked unless doctors are prepared to include them in their diagnostic framework. Some important pitfalls are given in Table A3.
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