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How to workup acute low back pain


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Introduction to acute low back pain

Today, we’re going to focus on the approach to your adult patient who comes in complaining of acute low back pain. Over 80% of adults will have this complaint at least once in their life time. Most of the time, it’s self limiting (90%), and will self resolve in 4 weeks – therefore, not much needs to be done.

I think it’s safe to say we’re all scared of missing something that can potentially cause the patient long term issues. First, let’s separate back pain in terms of duration:

<4 weeks = acute
4-2 weeks = subacute
>12 weeks = chronic

There are also a ton of terms you need to be aware of. If you have ever sent a patient for an xray then you have surely seen them. But, maybe you’re not 100% sure of what they mean. So, let’s briefly describe them.

Spondylosis: arthritis of the spine.
Spondylolisthesis: vertebra slips forward onto the vertebra below it.
Spondylolysis: fracture in the pars interarticularis aka the isthmus. It connects the facet joints.
Spinal Stenosis: narrowing of the spinal canal – presents with pseudo claudication (neurogenic claudication) – pain, weakness, and/or paresthesias are felt in the buttocks, thighs, and legs bilaterally. Worsens with walking and improves with leaning forward (shopping cart sign).

Differentiating psuedo claudication from vascular claudication: pedal pulses intact, symptoms are just as prevalent standing as they are with walking, and maximal pain is felt mid thigh (not the calf).

Possible Etiologies of acute low back pain

Most patients will simply come into your office complaining of non specific back pain – also known as mechanical back pain. This means they have back pain that is not associated with inflammatory disease or cancer.

Most of the time the pain will be worsened with activity and upright posture and relieved with rest. The most common identifiable cause is degenerative changes of the lumbar spine.

But, rarely, in can mean something a little more dangerous. Inflammatory back pain (spondyloarthropathies) typically worsens with rest and improves with activity. The patient may also have morning stiffness that lasts at least 30 minutes.

You do not need to order imaging studies for these patients. There are, however, exceptions (<1%), and these are the patients we have to look out for. So, who are they?

Well, there are three major medical conditions we should be on the lookout for: cauda equina syndrome, cancer, spinal infection (osteomyelitis and spinal epidural abscess).

Cauda equina

is most commonly a result of metastatic tumor and is actually the initial presentation of cancer in up to 20% of patients. Other things that can lead to cauda equina are hematoma, abscess, and/or disc herniation. Apart from pain, you want to look for weakness, numbness (saddle anesthesia), paresthesias, and motor deficits not localized to a single unilateral nerve root. Bladder/bowel dysfunction is a late finding.

Cancer Metastasis

The bone is the most common site of metastasis. So, anyone with a history of cancer and new onset back pain should be worked up for metastasis and pathological fracture.

Spinal infection

Patients with epidural abscess will also present with a fever. There should be suspicion of an abscess in patients who are immunocompromised, are injection drug users, and in those who have had recent spinal injection or epidural catheter placement.

Osteomyelitis presents as a gradual worsening of pain over days. Patients may or may not have any other symptoms. Incidence increases with age. The most common etiology is staphylococcus aureus, followed by E-coli.

If suspicion for one of the major three serious medical condition exists, then immediate imaging and referral should be done. Disc herniation occurs when the pulposus pushes through the disc – typically posterolaterally. Less than 1% of patients will have this and this is only an issue when this soft jelly like substance is pushing on a nerve root. This is also commonly found in asymptomatic patients – so be careful with imaging!

Also, 95% of clinically significant herniations will involve the L5 or S1 nerve roots – which ultimately results in sciatica. Therefore, if sciatica symptoms are not present – then seeing a disc herniation on MRI is more than likely NOT the cause of the patients back pain.

Most patients will have symptoms resolve on their own in a few weeks. Less than 10% of patients will need surgical decompression.

Initial Workup As stated above, <1% will have a serious medical condition that needs urgent workup. So, the history and physical should be geared towards ruling those conditions out first.

The history and physical typically does not lead to a specific diagnosis. Key questions to ask:

1. location/duration/severity
2. weight loss
3. night sweats
4. history of cancer
5. trauma
6. medications tried
7. neurological symptoms
8. injection drug use
9. chronic corticosteroid use

After gathering a careful history a physical exam should be done. But, as we said, most of the time the patient will have non specific back pain. This means the initial physical exam is used to assess the need for further imaging, not to uncover the etiology.

Step 1: Look at the curvature of the back (scoliosis or hyperkyphosis)
Step 2: Push on the spine to look for tenderness. Seen in fracture, infection, and metastasis. A step off can be seen in spondylolisthesis.
Step 3: Inspect the hip – tenderness over the greater trochanter is seen in trochanter bursitis (mistaken for LBP).
Step 4: Perform a neurological exam. If radiculopathy is present, focus should be on L5/S1 nerve roots. L5/SI – Distribution of Pain, Sensation, Weakness, Stretch Reflex L5/S1 nerve roots will cause pain that radiates to the buttocks, lateral/posterior thigh, lateral/ posterior calf, plantar foot, and/or toe. Numbness will be felt in the lateral/posterior calf, plantar/dorsum of the foot, and/or the in the webspace between the first and second toe. Weakness is felt during hip abduction/extension, knee flexion, plantar flexion, toe extension/ flexion, and foot inversion/eversion. Stretch reflex is lost in the achilles tendon (ankle). L4 nerve root – loss of dorsiflexion of the foot, loss of sensation over the medial aspect of the foot, and loss of knee reflex.
Step 5: Leg raise – useful to see if symptoms are radicular. Straight leg raise: the patient lies supine with foot dorsiflexed. Raise the patients leg (side where symptoms are present) – making sure the patient does not assist in lifting. A positive sign is a presence or worsening of radicular pain – NOT low back/hamstring pain. If the radicular pain is unchanged – this is a negative sign. Contralateral leg raise: Done the same as the straight leg raise, except you are lifting the leg opposite to the symptomatic side. Has a higher specificity, but isn’t as sensitive for disc herniation.
Step 6: Make sure the back pain is not due to psychological causes. A few things that give this away are very superficial tenderness, straight leg raise that improves while distracting the patient, non dermatomal distribution of pain/sensory loss, inconsistency with other movements like watching the patient get off the exam table, and/or pain elicited by pressing down on the persons head and/or while rotating the body. These signs are known as Waddell’s signs. Multiple positive signs indicate a possible psychological problem.

Are labs needed?

Typically no. The exception might be if infection or malignancy is a worry – then order ESR/CRP. Imaging If those 3 medical conditions discussed earlier are not of concern, then imaging is not truly warranted. Why? Because there doesn’t seem to be improved outcomes with early imaging.

Also, realize that the radiation exposure to the female gonads from the standard view of the lumbar spine is the same as having daily chest x-rays for several years.

The only thing that seems to happen is the over use of more invasive procedures – which are unwarranted to begin with. This is because there may be abnormalities seen even in patients who are asymptomatic.

It is believed that disc herniations are seen in up to 60% of asymptomatic adults and spinal stenosis is seen in up to 60% of asymptomatic patients over the age of 60.

Also, resolution of imaging findings does not correlate with patient outcomes. Some common findings that don’t seem to have any clinical significance: annular tears, schmorl’s nodes, and modic changes.

Annular tears: tears in the annulus fibrosus of the intervertebral disk.
Schmorl’s nodes: represents nucleus pulposus herniation into the adjacent disk.
Modic changes: bone marrow and endplate changes adjacent to degenerative lumbar intervertebral discs.


Indications for imaging in acute low back pain

The 3 main imaging modalities will be MRI, CT scan, and plain X-ray. The best initial test will be MRI without contrast.

CT scan is the next best test when an MRI can’t be performed. X-rays are generally indicated when a possibility of infection or malignancy is suspected.

Typically you will be ordering AP and lateral views. You can use MRI with contrast for patients who have had spinal surgery in the past – this will differentiate scar tissue from another disc herniation.

Red Flags: older age (50 – 70 years of age), prolonged use of corticosteroids, severe trauma, presence of contusion, nocturnal pain, and history of cancer.

We discussed cauda equina earlier, but to recap: Cauda equina is most commonly a result of metastatic tumor and is actually the initial presentation of cancer in up to 20% of patients. Other things that can lead to cauda equina are hematoma, abscess, and/or disc herniation.

Apart from pain, you want to look for weakness, numbness (saddle anesthesia), parasthesias, and motor deficits not localized to single unilateral nerve root. Bladder/bowel dysfunction is a late finding.

MRI is the imaging modality of choice for cauda equina Infection: If neurological symptoms are present – order an MRI. If a high level of clinical suspicion exists but there aren’t any neurological abnormalities – order an MRI. MRI has a 96% sensitivity and 92% specificity for infection.

If a low level of suspicion exists and there aren’t any neurological abnormalities – order an x-ray with ESR. If you have a positive x-ray – then you need to further evaluate depending on the results. If you have an elevated ESR, but a negative x-ray – order an MRI.

X-rays can often be normal when the infection is just starting. It is about 80% sensitive and 57% specific. Infection is VERY unlikely when the ESR is less than 20. Things that might increase suspicion: recent spinal procedure or history of IV drug use, fever, and localized tenderness.

Cancer: Patients who have cancer (breast, prostate, lung, thyroid, kidney, multiple myeloma) should have their oncologist consulted. Patients who have a high risk of cancer should have x-ray plus ESR done. If the patient has a negative x-ray but an elevated ESR – order an MRI.

What’s high risk? There’s no definition. But, you are looking at age, smoking, family history, rapid weight loss, etc. If the ESR is less than 20 and there is 1 risk factor or less – cancer is unlikely.

Patients who have a low risk for cancer, back pain, and no neurological abnormalities are treated with observation.

Compression fracture: Risk factors include history of glucocorticoid use, over 70 years of age, trauma, osteoporosis, or noticeable contusion. Patients will describe severe and sudden onset of pain with focal tenderness.

If the suspicion for a fracture exists – order an x-ray.

Treatment of acute low back pain

Like we said, most patients will have conservative management. This means patients should continue with their daily living and should not have bed rest of more than a couple days.

Typically, you’re going to want to give your patients NSAIDs and muscle relaxants if you feel there is also muscle spasm.

Glucorticoids are often given, but really have no proven benefit. Physical therapy is also unnecessary for initial management.

Follow up imaging

So, what do we do with patients who weren’t initially imaged, but still present with low back pain? If symptoms persist after 4-6 weeks – then you should reevaluate the patient and assess the need for imaging using the same history and physical exam we discussed earlier.

If the patient was imaged during the initial visit, symptoms persist, but are unchanged – then repeat imaging isn’t warranted.

But, if there are new or worsening symptoms, then you should image the patient again. If you are worried about ankylosis spondylitis – order an x-ray of the sacroiliac joints.

Also, keep in mind that arthritis of the hip and pelvis can lead to deferred pain of the lower back. If the pain is bilateral, order a standing pelvis film. If there is pain only on one side – order a standing frontal and frog leg view x-ray.

If the patient returns and there still aren’t indications for imaging – continue to treat conservatively for another 6- 8 weeks – a total of 12 weeks. If the patient continues to have symptoms after 12 weeks and there still isn’t improvement in symptoms, then go ahead and image the patient at this point, although the likelihood of finding any abnormality is low.

Most of the time (80%) a specific diagnosis will not be reached. The important thing is to rule out an serious etiology during the initial visit of non specific back pain.

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