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Diagnosing Acute Low Back Pain in Primary Care

A drawing of a spine
Photo by Joyce Hankins on Unsplash

Here’s the secret about diagnosing low back pain – 99% of the time, all you need is a good history and physical.


In the first post on acute low back pain, I wrote about finding the 1% of patients who have urgent pathology or nonspinal causes of pain. In this post, I want to show you the simplified way that I think about making the diagnosis.


The same caveats apply from Part 1: I’m talking about back pain that’s been going on for less than 2-4 weeks in a patient who presents to their family doctor or nurse practitioner.


I used this CMAJ article for this post.


Part 2: Diagnosing Acute Low Back Pain


Diagnosing low back pain is straight forward – do a good history and physical, identify cause for concern, and provide the patient with an understandable diagnosis.


The best summary I've found is from the CMAJ, which I've included below.


An algorithm for the diagnosis of low back pain
From https://www.cmaj.ca/content/189/45/e1386

The first step in diagnosing low back pain is to check whether there’s cause for concern. In primary care, only 1% of patients will have a sinister cause of low back pain (think fracture, infection, or cancer.) Check out Part 1 for my approach to weeding out that 1%.


Once you’ve assessed for sinister pathology and pain that’s coming from outside of the spine, there are only two types of low back pain left: nonspecific low back pain, and radicular pain/neurogenic claudication.


Nonspecific low back pain


By far, the most common type of low back pain is nonspecific. Ninety to 95% of patients in primary care will have this diagnosis.


But what does this actually mean?


Back in the day, we used to try to root out anatomical causes of back pain. Is the pain coming from a facet joint? A muscle? A nerve? A disc? A ligament? What we’ve found is twofold:


  1. We’re bad at determining the anatomical source of pain, because pain isn’t that straightforward, and

  2. determining the exact anatomical source of pain doesn’t change our management.


When I diagnose nonspecific low back pain, I say something like this:


“From my assessment today, I really don’t think your pain is coming from something that needs urgent testing. I think you have the most common kind of low back pain, which is nonspecific low back pain.


This means that we don’t know exactly where it’s coming from in the back, but it’s going to get better on its own. I expect your pain to feel better within the next two weeks without any treatment. In some cases, pain can last longer, so we’re going to talk about what to do to try to reduce the risk of that happening.”


Then, I go into my management for back pain, which I’ll write about in Part 3.


If people aren’t satisfied with this explanation, here’s my next spiel:


“Nonspecific pain is by far the most common cause of low back pain. It has this name because there are a lot of different factors that come together and influence pain. It’s almost impossible to pinpoint one source of pain in this case.


The pain could be coming from muscle, bone, ligament, nerve, or any other type of irritation. It can be influenced by things like stress, lack of sleep, inactivity, and smoking/alcohol.


In the end, we don’t have a good way to determine what part of your back is causing the problem. However, we know a lot about how to treat it and make it feel better.”


This usually does the trick. This is partially because I’m confident that there’s no test I can order that would help determine the source of a nonspecific pain syndrome.


When I was a physiotherapist, I had patients suffering from horrible pain in their backs but their MRI was pristine. I also had patients who had imaging showing a large disc herniation, but their pain went away in a couple of weeks with conservative treatment.


I let patients know that I’m not holding out on them – it’s called nonspecific because we don’t have a good way to find the exact cause, but it has a good prognosis.


Radicular Pain or Neurogenic Claudication


These two types of pain make up 5-10% of acute low back pain.


Radicular pain means that symptoms like pain, sensation changes, and weakness, are travelling along the path of a particular nerve root.


Neurogenic claudication describes symptoms of bilateral lower body pain coming from the spine, associated with things like spinal stenosis.


What do I do with these types of pain in practice?


I treat them like they’re nonspecific low back pain unless they have one key feature – weakness.


If a nerve root is seriously affected, there will be objective weakness along the path of that nerve. True weakness is consistent, so make sure to test for weakness in different ways if you think pain is interfering with the exam.


In the case of weakness along a nerve’s path, I first re-check my history and physical to make sure I didn’t miss symptoms of cauda equina (like saddle parasthesia, bowel or bladder changes, and bilateral leg weakness).


Then, I check their function. If they can’t function because of weakness, or if they have symptoms of cauda equina, I’m going to send them to the emergency department for a spine surgeon’s assessment.


If their function is preserved, I consider sending them for imaging to check if a nerve root is being compressed, or to see if there’s central canal stenosis.


Without objective weakness on exam, my management plan is the same for nonspecific pain as it is for neurogenic claudication/radicular pain. When I talk about the diagnosis, the only thing I would change is to say this:


“From my assessment, it seems like you have irritation in one of the nerves that travels from your back and into your leg. This isn’t dangerous, but it feels horrible.


It should get better on its own over the next few weeks. Sometimes, recovery can take longer, but we’re going to go through things that can reduce this risk.”


As we’ll get to in the next part of this series, it’s essential to provide patients with a written follow-up plan, especially in the case of weakness.


In summary


  • the majority of patients with low back pain in primary care have nonspecific low back pain

  • nonspecific pain has a good prognosis and gets better on its own

  • one in every ten patients will have radicular pain/neurogenic claudication, which can initially be thought of as nonspecific low back pain unless there’s weakness

  • if there’s objective weakness, consider sending your patient for urgent assessment if it's affecting their function


I hope I made things a little clearer when it comes to the diagnosis of acute low back pain. Let me know in the comments if you have questions!


Stay well friends,


Dr. Kuhnow

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