An Introduction to Medical Diagnosis (1)

“The student of medicine has to learn both the ‘bottom up’ approach of constructing a differential diagnosis from individual clinical findings, and the ‘top down’ approach of learning the key features pertaining to a particular diagnosis. In this textbook we have integrated both approaches into a coherent working framework that will assist the reader in preparing for academic and professional examinations, and in every day practice. […] We have split this textbook into three sections. The first section introduces the basic skills underpinning much of what follows – how to take a history and perform an examination, how to devise a differential diagnosis and select appropriate investigations, and how to record your findings in the case notes and present cases on ward rounds. The second section takes a systems-based approach to history taking and examining patients, and also includes information on relevant diagnostic tests and common diagnoses for each system. Each chapter begins with the individual ‘building blocks’ of the history and examination, and ends by drawing these elements together into relevant diagnoses. […] The third and final section of the book covers ‘special situations’, including the assessment of the newborn, infants and children, the acutely ill patient, the patient with impaired consciousness, the older patient and death and the dying patient.”

The above quote is from the preface of the book. This is a medical textbook with 500 pages and 26 chapters written by 27 contributors, so it has a lot of stuff; I’ve been conflicted about how to blog it for this reason. It has as lot of stuff which is useful to know but which most people don’t, and I think it’s the sort of book I might be tempted to ‘consult’ later on; the various 100 Cases… books I’ve read include some similar useful observations, but I think it’d be more natural to consult this book first because it’s much more likely that this book will at least have something about the medical condition you’re curious/can’t remember the details about. I think it was somewhat easier to read than was McPhee et al., and I’m not sure this is only because I read the former first (while I was reading McPhee et al. I was learning part of the vocabulary which is needed to read this book).

In the coverage below I have not talked about the stuff included in the first part; I don’t need to e.g. be able to take a medical history and navigate medical records, and if some of my readers do I’ll assume they have the necessary skills already, or know where/how to obtain such skills. In this post I’ll focus on the coverage of major systems in part two, with my coverage focused on ‘key variables’, and, well, ‘stuff I found interesting’ – which also means that I won’t talk about stuff like ‘this is how you palpate a liver’ and ‘this is how you grade heart murmurs’ (the book also covers that kind of stuff in some detail). Nor will I tell you what Buerger’s test or Trendelenburg’s test are used for, or give you a full account of the many, many different types of ‘named medical signs’ included and described in the book (Charcot’s triad, Cullen’s sign, Grey Turner’s sign, Murphy’s sign, Courvoisier’s sign, Kussmaul’s sign, Levine’s sign, etc. …).

I may in my coverage of this book tend to focus more on acute conditions than on chronic conditions, in part because it seems more useful to me to know/remember whether or not someone is, say, having a heart attack than whether or not someone with chronic kidney failure will be bothered by pitting edema. I think this approach makes sense.

The book has split the systems coverage in part 2 up into 15 chapters – there are specific chapters about: *The cardiovascular system, *the respiratory system, *the gastrointestinal system, *the renal system, *the genitourinary system, *the nervous system, *psychiatric assessment, *the musculoskeletal system, *the endocrine system, *the breast, *the haematological system, *skin, nails and hair, *the eye, *ear, nose and throat, and *infectious and tropical diseases. Most of the book coverage is devoted to this treatment of individual systems, as these 15 chapters make up roughly 350 pages of the total. I found it, interesting, that there was close to zero overlap between the coverage in this book and Newman and Kohn’s text; I’m not quite sure what to think about that.

In this post I’ll mostly talk about the first three ‘systems’ chapters. When dealing with cardiovascular disease, the major symptoms are chest discomfort, breathlessness, palpitation (an awareness of the heartbeat), dizziness and syncope (‘transient loss of consciousness resulting from transient global cerebral hypoperfusion’), and peripheral oedema (usually ankle swelling, most often associated with heart failure, often worse in the evening). An important observation is that myocardial ischemia (‘the heart muscle doesn’t get enough blood/oxygen’) can cause breathlessness and chest discomfort, and “in many cases breathlessness is the predominant symptom (particularly in women).” Deep vein thrombosis can be asymptomatic, but it commonly causes pain and swelling in the affected leg – the main acute risk factor associated with the condition (which is not particularly rare among elderly people) is that the blood clot travels to the lungs and causes a pulmonary embolism.

Next, the respiratory system: “respiratory conditions are common – accounting for more than 13 per cent of all emergency admissions and more than 20 per cent of general practitioner consultations”. I was very surprised the number was that high! I can’t provide a source as the authors did not provide a source; there are no inline citations in this book, which is part of the reason why the book did not get five stars on goodreads. Six key symptoms of respiratory diseases are chest pain (that may be extended to chest sensations), dyspnoea (shortness of breath/breathlessness), cough (“the commonest symptom that is associated with pure respiratory disease”), wheeze, sputum production, and haemoptysis (coughing up blood/blood in the sputum – this is, perhaps unsurprisingly, often, but not always, a ‘red flag symptom’: “Current recommendations indicate that urgent referral to a hospital clinic should be made when patients have haemoptysis, are over the age of 40, and are current or ex-smokers. However, a young patient who has a small amount of streak (lines in sputum) haemoptysis in the context of an upper respiratory tract infection usually will not require referral”).

In respiratory medicine, cough duration is an important variable in the diagnostic context; I was surprised that even simple respiratory tract infections may cause cough for up to three weeks, and that this is not necessarily something to worry about. Longer than that and it’s however less likely to be due to a self-limiting condition, and is more likely to be due to either lung cancer or one of the many causes of chronic cough (cough is not chronic until it’s lasted longer than 6 months) – these causes include, but are not limited to, astma, COPD, and GERD. As should be clear from the above, both heart and lung conditions may cause shortness of breath, so you can’t always conclude that shortness of breath is a lung issue. This is of course far from the only symptom which may present in different disease contexts, and the heart and lungs are connected in other ways as well; for example problems in both systems may cause clubbing. When dealing with a case of pneumonia it’s useful to be familiar with the CURB 65 score to assess risk/severity. Lung cancer can be either ‘non-small cell’ or ‘small cell’ lung cancer – in terms of presenting symptoms they’re reasonably similar, but the latter is more often associated with paraneoplastic syndromes (though these are still rare in an absolute sense, presenting in 5% of small cell lung cancers and 1% of non-small cell lung cancers, according to the book). The most common symptom is a cough, followed by persistent ‘chest infections’ (which are of course not infections) and bloody sputum/coughing up blood – but “some patients have remarkably few signs.” In the context of acute conditions affecting the lungs, pleuritic chest pain is an important symptom; this means pain which is made worse by breathing and which often has a sharp and stabbing quality to it – acute onset pleuritic chest pain can be due to a pulmonary embolism (60% of patients with PE have acute onset pleuritic chest pain; in another 25% there is a sudden onset of acute breathlessness) or a pneumothorax (‘collapsed lung’ – may also cause acute breathlessness). Although the two conditions are different, if you have either of them you want to get to a hospital, fast – sudden onset pleuritic chest pain seems to me a very good reason to call for an ambulance/visit the local emergency department.

“The gastrointestinal system includes the alimentary tract from mouth to anus, the liver, hepatobiliary structures including the gallbladder, pancreas and the biliary and pancreatic ductal systems.” This is a big system. And it’s often hard to get a good look at what’s the problem: “Almost half of gastrointestinal problems are not associated with physical signs or positive test results. Hence, the diagnosis and management is often based entirely on the inferences drawn from a patient’s symptoms.” Difficulty swallowing is a ‘red flag’ symptom, because “many patients with this symptom will have clinically significant pathology.” Weight loss combined with worsening difficulty swallowing (solids first, liquids later) means that oesophageal cancer is likely to be the cause (this one has a really bad prognosis). A useful observation when it comes to distinguishing between angina (‘heart issue’) and heartburn (‘gastrointestinal issue’), which may cause somewhat similar symptoms, is that whereas angina is often worsened by physical exertion, heartburn is not and often occurs at rest. It’s worth noting that when dealing with gastrointestinal disorders, you can learn a lot by figuring out where exactly the pain is coming from – stomach pain isn’t just stomach pain. Pain localized to one specific section of the stomach is much more likely to be due to condition X than condition Y (e.g., pain in the right upper quadrant = maybe biliary obstruction or hepatomegaly; pain in the left lower quadrant = maybe diverticulitis or infectious colitis). This may not be particularly useful for people in general to know, but I thought it was interesting. Duration of pain is a key variable: “Sudden onset of well-localized severe pain is likely to be due to catastrophic events [and] [p]ain present for weeks to months is often less life-threatening than pain presenting within hours of symptom onset.” The authors point out that the severity of abdominal pain can be underestimated in elderly people, very young patients, people who are immunosuppressed and diabetics (the latter presumably due to autonomous-/diabetes-associated enteric neuropathy). “Presence of blood in the stool points towards either inflammatory bowel disease or malignancy, but in those with infective diarrhoea it is highly specific for infections with a invasive organism.” The authors mention a few pointers to specific nutritional deficiencies which are probably useful to know about – iron deficiency may cause a flat angle or ‘spooning‘ of the nails, and it may also (together with vitamin B12-deficiency) cause soreness/redness of the tongue. Redness and cracks at the angles of the mouth are also associated with deficiencies of iron and vitamin-B12, as well as deficiencies of riboflavin, and folate.

January 31, 2015 - Posted by | books, cancer, medicine

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