Low Back Pain: Red Flags & Management

Objectives: Recognize dangerous causes of low back pain. Understand that not all back pain needs imaging. Using critical history taking skills and physical exam findings, the astute clinical should be able to identify the “red flag” symptoms through developing an evidenced-based stratification for appropriate laboratory assessment, radiologic imaging, and appropriate referrals.

Introduction: Low back pain accounts for around 3% of all ED visits in the US and is the most common musculoskeletal complaint presenting to the ED. In addition to about 26% of the population reporting low back pain in the last three months, it is the most common cause of disability in the US. Of the patients that we see in the ED, 85% of them will have pain in their back that is nonspecific and not clearly related to another medical condition or nerve root impingement syndrome. These patients will not need ED imaging.

Acute low back pain is defined as pain lasting less than six weeks, while chronic back pain lasts more than 12 weeks. Most episodes resolve within six weeks, but failure to improve may suggest a more serious cause. Benign back pain is often described as pain that worsens with movement and improves with rest. In contrast, back pain resulting from a spinal infection or tumor may be described as severe pain that awakens one from sleep or pain that does not improve with adequate analgesic therapy. 

Anatomy: Before we begin, let’s start with a brief anatomy review (we promise to keep it short):

• L1= Diminished inguinal sensation, weakness in hip flexion, cremasteric reflex
• L2= Diminished inguinal sensation, weakness in hip flexion/adduction, cremasteric reflex
• L3= Diminished sensation to anteromedial thigh, weak quad adductors, patellar reflex
• L4= Diminished sensation to anterior leg/1^st toe/medial mal, weak hip flexion/quads (leg ext), patellar reflex
• L5= Diminished sensation to dorsal foot/middle 3 toes. Extensor weakness of hallucis longus and foot.
• S1= Pain in posterior thigh/leg/lateral foot. Diminished sensation to lateral foot/heel. Ankle plantar flexion.
  • Straight Leg Raise Test: patient supine as each leg is lifted to 70 degrees. (+) Test= pain radiates below the knee of the affected leg, and pain is worse in dorsiflexion. 91% sens/26% spec
    • (Reproduction of pain in back, glutes, or hamstrings is NOT a Positive Test)
  • Crossed Straight Leg Raise Test: performed on opposite leg that is affected, (+) Test= pain radiates below the knee of the affected leg, when unaffected leg raised, and pain is worse in dorsiflexion. 29% sens/88% spec

History and Physical:

History is queen as the presence of trauma, tachycardia, hypotension, or fever should all raise your suspicion for an etiology unrelated to musculoskeletal causes. Check out TABLE 1 for a list of other red flag symptoms. The presence of one or more should lead you to pursue further imaging and labs. Listen for heart murmurs, palpate the abdomen for distended bladder, enlarged aorta (throw the US on them). Sometimes a rectal exam is indicated but it is not to be done on ALL patients with low back pain. Patients describing radicular pain should be asked and examined for neurological deficits. Remember that >90% of herniations occur at L4/L5 or L5/S1 levels (focused examination in the foot and ankle). If no deficits are present, they can be referred for outpatient follow up without emergent imaging. 

Try the heel tap test and Waddell sign to assess for nonorganic causes of LBP. Also check out this great resource from Stanford for exam maneuvers in LBP.

Diagnosis: In most patients with acute low back pain, NO testing will be necessary. Do not waste your time imaging low-risk patients without red flags or non-focal symptoms.

• CBC, BMP, ESR, Urinalysis = only if there is a concern for a more sinister process. Never get these for “reassurance”.
• Lumbar XR = these are NOT indicated. If you are really concerned about a fracture or neoplastic process, get a CT. A cool study that looked at 68,000 radiographs, they found that clinically unsuspected lesions occurred in 1:2500 patients aged 20-50 years. These x-rays are a waste of money and radiation. Instead, just take the time to explain to the patient why an x-ray will not help their diagnosis or change outcomes. They will appreciate you even more.
• CT = provides a more detailed view of vertebral bodies. Can see nerve roots and large spinal masses. Good to use if MRI not immediately available and can rule out a lot of pathologies. Great for trauma.
• MRI = great view of spinal canal & cord; best for infection, neoplasm, & epidural compression. Always get “with and without contrast”. Please note that obtaining thoracic spine imaging in addition to the lumbar spine is needed in many cases, especially if cancer is a possibility, as the thoracic spine is the most common site involved.
  • Of note, there was a study of MRI imaging in asymptomatic patients aged ≥ 60. 36% had a herniated disc, 21% had spinal stenosis, and 90% had a degenerated or bulging disc. 

Regarding imaging in general, A meta-analysis of 6 randomized trials of 1800 patients found no outcome differences between routine care and no imaging and patients who underwent imaging with plain x-ray, CT, or MRI.

Nonspecific Back Pain (85% of back pain): (sprain, mechanical strain, lumbago). Most cases resolve on their own.

• Management = Analgesia + Monitor symptoms for 4-6 weeks
  • Resume normal activity to the furthest extent tolerable. Laying in bed all day is harmful for patients.
  • Medications: NSAIDs (Ibuprofen 400-800 mg TID or Naproxen 250-500 mg BID)
    • Use the lowest dose possible
    • Tylenol was previously recommended, but recent research shows no benefit
    • Muscle relaxants= Methocarbamol (1000-1500 mg QID)
      • Benzos work too but NOT recommended due to addiction potential
      • No synergistic benefit when combining NSAIDs and muscle relaxants.
        • Manipulation & heat therapy beneficial in some patients No role for corticosteroids (systemic, injections, etc.).
      • No proven efficacy= traction, diathermy, laser, electrical nerve stimulation.
      • Be very cautious using muscle relaxants in elderly patients. Caution with poly pharmacy as well. Muscle relaxants have an increased risk of falls.

• Sciatica: radicular pain involving a lumbar or sacral nerve root; sensory or motor deficits common; most cases seen in association with Herniations
  • Anything that impinges on spinal nerve roots, cauda equina, or spinal cord e.g., intraspinal tumor or infection, foraminal stenosis, piriformis syndrome.One small study found that gabapentin to be beneficial.

• Disk Herniation: leg pain worse than back pain; pain exacerbated with coughing, Valsalva 
  • Confirm via nonurgent MRI (if epidural compression suspected, then urgent MRI)
  • If no risk factors for serious disease (besides sciatica), may treat conservatively
  • If neuro deficits present= X-ray to eval for tumor, fracture, infection, spondylolisthesis 
  • If severe/progressive neuro deficits or serious disease suspected= recommend MRI
  • Management= Routine daily activity + NSAIDs
    • Limited opiates for severe pain 
    • Limited benefit with corticosteroids, muscle relaxants, & antiepileptics 
    • Epidural injection= small decrease in leg pain and sensory symptoms
    • Manipulation= small decrease in pain for up to 12 weeks 
    • Over half of patients recover within six weeks without surgery
    • Surgery may be considered if the following three conditions are met: 
      • Imaging that shows definitive disk herniation 
      • Corresponding clinical symptoms and neurologic deficit 
      • Conservative treatment for 4-6 weeks with no improvement

References: 

1. Cline, D., Ma, O. J., Meckler, G. D., Stapczynski, J. S., Thomas, S. H., Tintinalli, J. E., & Yealy, D. M. (2020). Tintinalli’s emergency medicine: A comprehensive study guide (9th         ed.). Retrieved November 12, 2020.
2. Chou R, Fu R, Carrino JA, et al. Imaging strategies for low-back pain: systematic review and meta-analysis. Lancet. 2009;373(9662):463-472. (Meta-analysis)
3. Vroomen PC, deKrom MC, Knottnerus JA. Diagnostic value of history and physical examination in patients suspected of sciatica due to disc herniation: a systematic review. J Neurol 1999;246:899-906.
4. Boden SD, Davis DO, Dina TS, et al. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg Am. 1990;72(3):403-408. (Prospective observational cohort)
5. Rider LS, Marra EM. Cauda Equina And Conus Medullaris Syndromes. [Updated 2020 Aug 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537200/
6. Simone CG, Emmady PD. Transverse Myelitis. [Updated 2020 Aug 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559302/
7. An Evidence-Based Approach To The Evaluation And Treatment Of Low Back Pain In The Emergency Department