An Introduction to Medical Diagnosis (II)
Here’s my first post about the book. In this post I’ll cover two more of the individual systems chapters – the first of the chapters I’ll talk about is the one about the renal system (kidneys). Some key symptoms which may suggest renal pathology are disorders of micturition (urination), disorders of urine volume, changes in urine composition, loin pain, oedema, and hypertension. Disorders of micturition can relate to frequency, poor urinary stream (typically caused by outflow obstructions) and dysuria (pain on micturition). There are 19 different causes of frequency mentioned in a table in the chapter, so there are a lot of possible causes. Volume changes may be termed polyuria (increase in volume), oliguria (decrease-), or anuria (total loss of urine output – this is bad); it’s important to note that frequency does not necessarily imply polyuria. Blood in the urine is called haematuria, a symptom which will often cause people to seek medical attention – for good reason: “Any patient above the age of 40 years with haematuria (visible or invisible) requires urgent evaluation by a urologist to look for malignant disease of the urinary tract.” It should however be noted that red/brown urine doesn’t necessarily indicate haematuria – other common causes are drugs and vegetable dyes – and relatedly it should be mentioned that blood in the urine may not be visible (haematuria is sometimes caught as an incidental finding by dip-stick analysis of the urine). When blood is present in the urine at the start of micturition only it usually indicates urethral bleeding, whereas bleeding towards the end of micturition is indicative of bladder/prostate bleeding. In the context of kidney disease pain patterns are inconsistent, but when there’s pain it’s usually due to renal tract inflammation or obstruction (e.g. due to a kidney stone). Cancer need not cause pain: “The cardinal feature of transitional cell carcinoma of the urinary tract is painless haematuria”, which may or may not be visible to the naked eye. In bladder cancer ‘local’ symptoms such as frequency and nocturia present before systemic symptoms such as weight loss, and the latter symptoms usually present late. Risk factors include smoking, occupational exposure to hydrocarbons, ionizing radiation (e.g. previous cancer treatment), prolonged immunosuppression, and bladder stones.
There are a number of inherited renal diseases, as well as a huge number of medical conditions associated with renal disease (18 of them are listed in the chapter). Aside from specific medical conditions a large number of drugs may also impact kidney function and the risk of developing renal disease. Pregnancy is a risk factor. Dietary factors may be important in some cases; for example excessive salt intake may lead to hypertension, as may alcohol, and hypertension is bad for the kidneys. Another example would be inadequate fluid intake or high intake of animal protein, both of which may promote lithiasis (stone formation). Tobacco is a significant risk factor for the development and progression of kidney disease. Of the many causes of kidney failure, diabetic renal disease is the most common cause of end-stage renal disease (-ESRD) in the Western world, according to the book accounting for 20-50% of new patients with end-stage renal disease (presumably the estimate is so broad-banded due to major cross-country differences). Another important cause is autosomal dominant polycystic kidney disease (ADPKD), which make up 10 per cent of patients with ESRD. Women have urinary tract infections (-UTI) much more often than men, and 50-60 per cent of women have at least one UTI during their lives. In males the risk has been estimated to be 5/10.000/year. It’s noted in the next chapter of the book that “Urinary tract infections (UTIs) are common in women, but uncommon in men under 50 years old”, but that “[o]lder men may get UTIs secondary to bladder outflow obstruction from prostatic hypertrophy”. I won’t talk much about that chapter, about the genitourinary system, as I’ve talked quite a bit about these sorts of things before when covering Holmes et al., e.g. here and here, but one other important quote is probably worth including here as well: “Seventy-five per cent of people infected with HSV [herpes simplex virus] are not aware that they have genital herpes either because their symptoms are very mild/absent or because the symptoms have been assumed to be due to something else (most commonly thrush).”
The other main chapter I’ll cover here is the chapter about the nervous system. I liked the way the author starts out the chapter – here’s a quote from the beginning of the chapter: “Inexperienced clinicians often order sophisticated (and expensive!) investigations hoping that the diagnosis may be revealed, but sadly this rarely happens. Many investigations are relatively sensitive but not necessarily disease specific”. Later on he also notes that it is his opinion that: “Electroencephalograms (EEGs) are grossly overordered. They should not be used as a diagnostic tool in epilepsy as they are relatively non-specific and non-sensitive.” I liked this stuff in part because I’m the sort of person who cares about cost-effectiveness, but also because Eysenck and Keane’s Cognitive Psychology text, part of which I read last December, contained some reasonably detailed coverage of various imaging methods used in these contexts and what you can and cannot use them for; and I think it’s highly likely that the author of the chapter is right. I may go into much more details about this kind of stuff later if I decide to cover E&K’s book, but I won’t talk about it here. One related observation worth including here is however that in the context of a seizure, something as ‘low-tech’ as an available eye-witness is often crucial (was there jerking? pallor? gaze aversion?) to make a diagnosis and distinguish between an epileptic seizure and a cardiovascular syncope (the most common diagnostic dilemma here).
Headaches are common. It’s useful to know that whereas an acute headache may be a sign of sinister pathology, chronic headaches rarely are. Acute headaches may be almost instantaneous (hyperacute), or they may develop over hours to days. Instantaneous headache may be (but of course needn’t be) due to life-threatening conditions such as subarachnoid haemorrhage, venous sinus thrombosis, cerebral haemorrhage, and phaeochromocytoma, all of which may present that way. The combination of neck stiffness and photophobia (together with headache) is called meningism and this is something that requires urgent investigation, as it may be due to meningitis or encephalitis. Muscle weakness is a common neurological symptom, and here it’s important to note that hyperacute limb weakness is usually caused by a stroke, and is most commonly unilateral (i.e. affecting e.g. only one arm or leg, rather than both), whereas bilateral weakness is a marker of spinal cord disease. Sensory symptoms may be either ‘positive’ (e.g. tingling, dysaesthesia) or negative (numbness); stroke usually causes negative symptoms, whereas various genetic or acquired disorders may also present with ‘positive’ symptoms as well. “Neuropathic pain (cf diabetes) is often lower limb predominant and described as burning, stinging or throbbing.” Relatedly: “Diabetes is the commonest cause of neuropathy in the UK; distal predominantly sensory neuropathy, diabetic amyotrophy (pain and wasting in femoral distribution), nerve entrapments (carpal tunnel syndrome), cranial neuropathy and autonomic neuropathy are relatively common complications.” As for the aforementioned strokes, they’re sometimes (in 15 per cent of cases, according to the book) preceded by a TIA (a transient ischaemic attack), a sort of ‘mini-stroke’ which causes a reversible neurological deficit lasting less than 24 hours (‘in practice much shorter duration’). A recent TIA puts you in high immediate risk of stroke, which is probably useful to know – for more details, see this link.
The nervous system deals with a lot of stuff, so a lot of things can go wrong. Autonomic nervous system disorders may cause symptoms/problems such as: sphincter disturbances (e.g. incontinence), change in sweating patterns, photophobia (when the pupil is affected), night blindness, orthostatic hypotension, dry mouth, dry eyes, erectile/ejaculatory failure, and vomiting. Specific nerves doing specific things can cause specific symptoms when they stop working the way they’re supposed to, and these sorts of symptoms are very far from limited to ‘people being unable to move their arms or legs’; neurological problems can also cause you to e.g. go blind or deaf. The distinction between monolateral (‘vascular’) and bilateral (‘neurological’) symptoms and how this distinction relate to the underlying medical cause seems to apply not only to major limbs, but also to other areas of the body – for example if you’re experiencing vision loss in both eyes it’s more often a neurological problem, whereas problems caused by retinal pathology tend to cause unilateral symptoms. On a related note, in elderly people monocular loss of vision can be a harbinger of stroke. They mention in this chapter that neurological dysphagia (difficulty swallowing) may affect liquids first, whereas a mechanical obstruction (e.g. due to a tumour) will preferentially affect solids (I mentioned this in my last post about the book). “The duration of anterograde amnesia is an extremely useful indicator of the severity of head injury.” In the last part of the chapter the author talks about various specific conditions causing neurological problems, such as Parkinson’s disease, Motor Neuron Disease, Multiple Sclerosis, Myasthenia gravis, and Guillain–Barré syndrome – I won’t cover these in any detail as the book only covers them very briefly (you can google them if you’re curious).
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