• Question: I have heard heath care professionals when diagnosing disease look for trends in symptoms, what if the symptoms don't fit the trend and are ambiguous? (Yet the person still has the same disease that fits the trend)

    Asked by indigoblue on 4 May 2020.
    • Photo: Ailith Ewing

      Ailith Ewing answered on 4 May 2020:


      Firstly, I am not a health care professional. You are right though that health care professionals do look for trends in symptoms in order to help diagnose a disease. They also use what are called ‘signs’. These are things that the health care professional can observe themselves. Often they include things like test results. Monitoring changes in both signs and symptoms can help health care professionals make a diagnosis. However, different people can respond differently to the same disease for a variety of reasons, this can mean that the trends in signs and symptoms can be slightly different between people. Healthcare professionals use their judgement and training as well as information available to them from resources such as medical research in order to decide what the most likely diagnosis is for any given patient.

    • Photo: Kim Liu

      Kim Liu answered on 4 May 2020: last edited 4 May 2020 1:46 pm


      Again – not a healthcare professional, and I’m not going to say too much other than I suspect this is a big contributor is why being a doctor can be a very, very tough job, not least because people’s lives are on the line!
      As Ailith has described – I think doctors will try to find as many ways as possible to make a diagnosis. Technically, symptoms such as pain or loss of sensation are subjective, so they only form part of the picture.

    • Photo: Delma Childers

      Delma Childers answered on 4 May 2020:


      Also not a health care professional, but I have trained medical students on how to diagnose infectious diseases. You’re right, sometimes it’s hard to diagnose infections because not everyone will present with the classic symptoms. Doctors have a variety of resources to help here – their training and judgement (as Ailith and Kim mentioned) and their colleagues, who may have helpful experience to share. There are also specialist institutions that take on really tricky cases, such as the hospital at the National Institutes of Health in the US. These cases can tell us a lot about how genetic variation in us can affect how symptoms of an infection change from person-to-person.

    • Photo: Wei Xun

      Wei Xun answered on 4 May 2020:


      Just an example of how clinical diagnosis can work, someone has developed an online tool for COVID-19/SARs-Cov2. So when a healthcare profession is presented with a list of symptoms from a patient, the tool shows how common that particular combination is in confirmed coronavirus cases. Take a look:

      https://coronavirus.kahun.com/Clinical%20Features/Fever

    • Photo: Nina Rzechorzek

      Nina Rzechorzek answered on 5 May 2020: last edited 5 May 2020 2:57 am


      Hi indigoblue – interesting question! I’m a healthcare professional for non-human animals (a vet), but the concepts and training are similar. Yes, we do look for trends in our patients; not only do we consider the combination of symptoms (humans) or clinical signs (other animals), we also carefully monitor the progression of those signs to help us with the diagnosis. For example, when it comes to brain diseases, rapidly progressive neurological signs are more likely with an infectious cause than with, for example, a slow-growing brain tumour. We also consider the ‘signalment’ of the patient i.e. the age, sex, ethnicity or other aspects of genetic background (in particular for canine patients, their breed) because some diseases are more common in certain age groups, or in females relative males etc. We use all of this information (signalment, clinical history, clinical examination of the patient) to formulate a ‘differential diagnosis’ list – a list of the most likely diagnoses. We then use a range of diagnostic tests to exclude or confirm each of these. From the above, it will be apparent that over time, and with more experience, clinicians use ‘pattern spotting’ to some extent. For example, if I am presented with an older dog of a certain breed with very acute neurological signs that get progressively better I’m going to think more of a vascular cause (like a stroke) than a tumour. However, it’s important not to jump to conclusions without a ‘definitive diagnosis’ – a sudden bleed from a brain tumour is effectively a stroke that is secondary to another underlying cause, and unless we perform a brain scan, we will miss it, and potentially miss the opportunity to treat the primary cause more effectively at an earlier stage. Equally, we don’t want to put any patient through endless diagnostic tests that might be unnecessary if we had narrowed our differential list appropriately in the first place – so we always need to weigh up the benefits and risks to patient of any given test, and try to rule in/out the most likely things first. You are absolutely correct in that not all patients ‘read the textbook’ – i.e. many patients will not present in exactly the way you might expect, nor may they express all the symptoms/signs of a given disease. These are the most challenging cases, often requiring prolonged work-up with many tests before we reach a final answer. Sometimes we have to treat ‘presumptively’ in order to control symptoms/signs and prevent suffering when we’re not sure of the underlying cause – and sometimes the response of the patient’s symptoms/signs to treatment can give us the diagnosis. Sadly, there are cases when a definitive diagnosis can only be reached after death – this is quite common for neurodegenerative diseases where a pathologist needs to the look at the brain tissue in order to be sure of what was wrong with that patient. In essence, making the right diagnosis is all about problem solving – some puzzles are easy and quick to solve; others can take months or even years! Some patients have more than one disease at the same time which can make things especially tricky! The important thing is always to keep listening to the patient (or their owner) to check that we have understood the nature of the problem, its progression, and whether it is responding to treatment or needs further investigation.

    • Photo: Roberta Migale

      Roberta Migale answered on 5 May 2020:


      I’m not an healthcare professional but your question can be answers by a scientist like me who looks for trends in the ways cells behave for example. I often works with different “patients” (that is different bunch of cells) which all have the same “disease” (that is for example in my case they lack a particular gene so they do not work properly). Each bunch of cells can in fact behave in a slightly different way from the other even though they may all carry the same “disease”. That is why observing a high number of cells (or patients) at the same time and for a long period of time is often a good approach to obtain a correct diagnosis. As scientist we write papers in which we describe how the cells have behaved in different conditions, clinicians also do that by writing papers after having observed how a patient has responded to treatment or how he/she develop symptoms of a particular disease. All this information based on experience is what we call “scientific literature”. Both healthcare professional and scientists refer to it to improve their chances to get a diagnosis right. Although is possible that some symptoms may not be typical, it is also possible that they have been observed in some other cases and somehow have been associated with a particular disease. That is why being thorough in your assessment, talking to other experts and be open to all possibilities is very important for a diagnosis which is as accurate as possible.

    • Photo: James Loan

      James Loan answered on 5 May 2020: last edited 5 May 2020 10:37 am


      Hi indigoblue,

      I’m a doctor who works doing neurosurgery – surgery on the brain and spine. Your question goes right to the heart of what it is to be a doctor – what is a disease? When a patient sees a doctor they will usually complain of something that is making them feel unwell. These symptoms may fit a pattern that we recognise and we can make an informed guess as to what might be causing them. Sometimes we can do tests – for example scans or blood tests – to help give us more information.

      However, surprisingly frequently, these can all be misleading. As you say the person may have symptoms that don’t fit a clear trend or pattern. Or they may fit a trend or pattern for one disease, but that could be the wrong one. Or they may have a known pattern of symptoms – a “syndrome” – but scientists haven’t yet figured out what causes it: this was the case at the start of the covid pandemic, for example. Because there is often a large amount of diagnostic uncertainty, especially when you are seeing a patient for the first time, doctors also need to work on treating the symptoms, signs (things that you can measure – like low blood pressure), and results from investigations.

      For example, a patient might present to their GP with headaches, fevers and a weak arm. All of these symptoms are quite common and often not dangerous. However, in combination they don’t point to any one diagnosis. Although there isn’t yet a cause for the symptoms the doctor should start treating the headache and fever – paracetamol might help. In the meantime because pain in the head with a “nerve” symptom – arm weakness – could mean a brain problem, it would be important to arrange a scan of the brain to see if there was anything going on there, for example a stroke.

      This CT scan may then show something funny – not a stroke, but a swelling that can’t be seen very well. Again we don’t have an answer but we are getting closer. We know that growths in the brain could be tumors, or infections – abscesses. Depending on how generally sick the patient is, it might be sensible then to give them antibiotics, while another special scan – called an MRI – is arranged. This will give us more information. The patient should usually be referred urgently to a neurosurgeon at this stage.

      To finish the case, the scan shows an inflammed area in the brain with a hole in it filled with thick fluid. This sounds most like an abscess, but could also be an unusual type of tumor. The patient will often then undergo surgery to remove the problem area. This will stop any infection or tumor spread and will also give a sample of tissue to send to the lab for scientists to look at under a microscope and see if it looks like a tumor or an abscess. Lets say it is an abscess – we then have to ask is there an underlying cause for why this person got an infection in the brain… and so on

      So you can see that each step of the process of diagnosing a patient there is uncertainty, and the trends or patterns rarely fit just one condition. The patient shouldn’t have to wait for a diagnosis before getting treatment and so doctors have to make educated guesses about what is most likely to be going on and also treat symptoms, rather than their underlying cause. At the same time we have to keep hunting for more information until we have enough information to get the patient feeling fully better. We also have to be wise enough to know when to stop looking for problems: this whole process is scary, stressful and often painful for patients.

      Sorry for the long answer – hopefully it was helpful to have an illustrated case! Great question 🙂

    • Photo: Freya Harrison

      Freya Harrison answered on 6 May 2020:


      Did you know that a lot of the “textbook” symptoms for diseases were based on studies of men, but not women? For instance, when you think of someone having a heart attack you think of people having pains in their chest and left arm. That’s what men typically get when they are having a heart attack, but these symptoms are not so common in women. For example, woman having a heart attack might have stomach pains and sickness, which feels like severe food poisoning. This was not fully understood for a long time, so the death rate from heart attacks was higher for women than for men – doctors did not recognise their symptoms as being a heart attack. So in that case, the result of the symptoms not fitting the known trend was that people didn’t get the right treatment. This is why studies of disease need to include diverse patient groups.

    • Photo: Bilal Ahsan

      Bilal Ahsan answered on 11 May 2020:


      James already has given a detailed answer.
      I am not a medical doctor but have the privilege of working as a medical technologist in the pathology lab of a hospital.
      Diagnosis is a combination of what patients tell, what a doctor asks’, what a doctor suspects, physically examines and finally, in most cases, verifies by laboratory tests.
      If the symptoms are ambiguous, it pushes the doctor to go deeper into the investigation – for instance, to include additional tests such as Full blood count, Renal function tests, Liver function test, Lipid profile and even X-ray/Ultrasound – that he wouldn’t request otherwise. In extreme cases, it possibly could resemble hit and trial method.

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