EM@3AM: Back Pain

Author: Hannah Ceen, MD (EM Resident, NMCP, LT MC USN), Eric Sulava, MD (EM Chief Resident, NMCP, LT MC USN) // Edited by: Brit Long, MD (@long_brit, EM Attending Physician, San Antonio, TX), Alex Koyfman, MD (@EMHighAK)

Welcome to EM@3AM, an emDOCs series designed to foster your working knowledge by providing an expedited review of clinical basics. We’ll keep it short, while you keep that EM brain sharp.

A 59-year-old man with history of HTN, HLD, DM2, and smoking presents to the ED for acute onset low back pain that started immediately after he moved furniture. He states his lumbar pain has been unrelenting, with mild pain radiating to down both legs.  He now feels like he is ‘tripping over his feet’.

Initial Vitals: HR 89, BP 132/86, RR 20, SpO2 98%, Temp 98.6⁰F

Exam: He appears in pain and has mild midline and bilateral paraspinal tenderness to palpation over his lumbosacral spine.  He has bilateral loss of strength in the distal lower extremities, notably with dorsiflexion.  He has numbness in his bilateral feet.  3+ reflexes noted with patellar and Achilles testing.

What diagnoses should you consider? What’s the next step in your evaluation and treatment?

Answer: Conus Medullaris or Cauda Equina Syndrome



Low back pain is among the most common presenting complaints in the ED, and while most of the patients end up having acute non-specific back pain, there are several very serious causes of low back pain that can have devastating consequences if not detected and treated promptly.


Risk factors:

Age, female gender, obesity, smoking, physically demanding or sedentary work, psychologically strenuous work, and psychologic factors (e.g. depression, anxiety, somatization disorder).



More concerning:

  • Major trauma – MVC, fall from height, sports injury, violence
  • Minor trauma – Mechanical fall in elderly and patients with rheumatologic disease
  • Infection (osteomyelitis, spinal epidural abscess)
  • Pathologic fractures
  • Acute epidural compression syndrome (spinal cord compression, cauda equina syndrome, conus medullaris syndrome)
    • Conus medullaris syndrome involves the distal part of the spinal cord, at the L1-L2 vertebral level
    • Cauda equina syndrome involves the lumbosacral nerve roots, at the L2-sacrum vertebral level
  • Vascular: Spinal epidural hematoma, ruptured or leaking AAA

Less concerning:

  • Nonspecific low back pain/strain (diagnosis of exclusion)
  • Monoradicular pain (sciatica)


History and Exam

History Red Flags

  • Age>50 or <16 years
  • History of cancer (or symptoms concerning for cancer – e.g. unintentional weight loss, fevers, chills, night sweats)
  • Immunodeficiency (HIV, DM, on immunosuppression meds including steroids)
  • History of IV drug use
  • History of trauma
  • Acute epidural compression syndrome – saddle anesthesia, bowel incontinence, urinary retention/incontinence, bilateral LE weakness, sudden onset erectile dysfunction
  • Fever
  • Severe pain that awakens patient from sleep or pain that is worse when patient is supine
  • Anticoagulation
  • Recent LP/epidural or other spinal procedures


Physical Exam:

  • Palpate spinous processes for tenderness
  • Soft tissue exam for muscular tenderness
  • Check for signs of spinal cord compression
    • Bladder distension: New urinary retention (Post void residual should <100 in patients with normal urinary function) or urinary incontinence from bladder overflow
    • Saddle anesthesia
    • Digital Rectal Exam: Decreased rectal tone or new fecal incontinence
    • Perineal Reflex: Noxious or tactile stimulus will cause a wink contraction of the anal sphincter muscles
    • Bulbocavernosus reflex: Stimulation of the dorsal penis/clitoris nerves with the reflex response of anal sphincter contraction
    • Motor deficits not localized to a single nerve root
  • Neurologic exam: Strength, sensation, reflexes, coordination, and gait abnormalities
  • Monoradicular neurologic findings
    • Positive straight leg raise test (68-80% sensitive for L4-L5 or L5-S1 herniated disk)
    • Positive crossed straight leg raise test (radicular pain down affected side when lifting the asymptomatic leg)
    • Sensory, strength, or reflex deficits along a specific nerve distribution (L4, L5, S1)


  • Use the physical exam to help differentiate between cauda equina and conus medullaris syndromes:
    • Symptom onset:
      • Conus medullaris tends to present with more abrupt onset of bilateral symptoms, associated with severe low back pain
      • Cauda equina tends to have a more gradual onset of symptoms, and they can often be unilateral, associated with severe radicular pain
    • Incontinence: Fecal and urinary incontinence seen earlier in conus medullaris, whereas in cauda equina they tend to be a much later sign
    • Sensory exam:
      • Conus medullaris presents more often with symmetrical sensory loss, centered around the peri-anal area
      • Cauda equina more often has asymmetrical sensory loss, centered around the “saddle region”
    • Reflexes:
      • Conus medullaris can present with hyperreflexia, with the achilles reflex most often affected
      • Cauda equina tends to present with hyporeflexia, with patellar and achilles reflexes affected


Laboratory Assessment

Most patients do not require any laboratory workup, however if the patient has red flags concerning for infection, cancer, or rheumatologic disease, the following labs may be useful:

  • CBC (WBC count may be elevated in infection)
  • ESR ( >20 mm/h, sensitivity of 90-98% for spine infection, may also be elevated in patients with cancer or rheumatologic disease)
  • CRP (elevated in acute spine infection)
  • UA (infection of urinary tract may cause referred back pain)



Imaging for low back pain without associated symptoms causes no difference in outcomes, but increases the use of invasive procedures. Therefore, a majority of patients will not need imaging in the acute setting.

  • American College of Physicians (ACP) / American Pain Society: “clinicians should not routinely obtain imaging or other diagnostic tests in patients with nonspecific low back pain”
    • reserve imaging for patients with severe or progressive neurologic deficits or when serious underlying conditions are suspected on the basis of history and physical examination
  • National Institute for Health and Care Excellence (NICE) (UK): “not routinely offer imaging in a non-specialist setting for people with low back pain with or without sciatica”

Determining the necessity for a radiologic study revolves heavily around a thorough history and physical exam.  The main imaging modalities for evaluating back pain are MRI, CT, and plain films.


When to obtain imaging:

  • Immediate MRI if suspect acute spinal cord compromise
  • Immediate MRI for high suspicion of infection or metastatic disease
    • If lower suspicion of infection, start with ESR/CRP and consider MRI if elevated
    • If lower suspicion of metastatic disease, review their most recent imaging and consider starting with plain films
  • Thoracolumbar Trauma: if history and physical exam suggest high risk for structural injury (plain film or CT as below)
    • Signs of injury
      • Focal pain or tenderness over the spine – palpable step off – overlying hematoma
      • Neurologic deficit consistent with Thoracolumbar injury
    • High-force mechanism
    • Presence of another spine injury (known cervical fracture)
    • Painful distracting injury
    • High risk population
      • Age > 60 years
      • Depressed mental status
      • Rheumatologic disease).



As above, when there are “red flag findings” concerning for spinal cord / ligamentous involvement, neurologic compromise, cancer/metastasis, or infectious spread: MRI without contrast is the best initial examination.  It will identify the vertebral discs, ligaments, nerve roots, and size/shape of the spinal canal.

  • Sensitivity and specificity of MRI for herniated discs and spinal stenosis is similar to that of CT (88-94%). However, nerve roots are better visualized on MRI
  • For infection, MRI is the most sensitive (96%) and specific (92%) imaging modality
  • For cancer, MRI has the highest sensitivity (83-93%) and specificity (90-97%)

Plain Films / CT:

As above, this is going to be reserved for bony abnormalities and mass effect.  For cancer and low mechanism injuries in a high risk population, plain films are appropriate screening exams.  Further imaging may be required if abnormalities are found. When using plain radiographs, anteroposterior and lateral views of the lumbar spine are usually adequate. Oblique views substantially increases the radiation dose and adds little new diagnostic information.  CT scans can evaluate for multiple injury sources simultaneously in major trauma.  Additional plain films are usually not required if a CT of the abdomen and pelvis are already being performed.


Management / Treatment

  • Acute epidural compression syndrome (spinal cord compression, cauda equina syndrome, conus medullaris syndrome):
    • MRI emergently
    • Consult spinal specialist (neurosurgery/orthopedics)
  • Spinal epidural abscess or osteomyelitis:
    • Start antibiotics after obtaining blood cultures (make sure to include MRSA and gram-negative coverage)
    • Patient may require surgery
  • Spinal metastasis:
    • Consult oncology
    • Give at least 10mg dexamethasone IV to patient with neurologic symptoms
    • MRI urgently if signs of cord compression, within 24 hours if any neurologic symptoms present, within 7 days if x-ray/CT shows metastasis but there are no neurologic findings
  • Spinal epidural hematoma in anticoagulated patient:
    • Reverse anticoagulation if possible
    • Patient may require surgery
  • Monoradiculopathy:
    • See management of nonspecific lumbosacral pain
    • Patient will require follow-up with primary care doctor to further assess need for non-emergent MRI
  • Nonspecific lumbosacral pain/sprain (once more concerning etiologies ruled out):
    • Symptom management: NSAIDs, acetaminophen, muscle relaxants, light activity/stretching, heat, and physical therapy
      • Gabapentin may be beneficial for patients with neuropathic pain
      • Patients with severe pain may require opioids or even admission for pain control
    • Education and reassurance: Prolonged bed rest does not speed up recovery, 90% of patients improve over 4-6 weeks, good return precautions including red flag symptoms


Don’t forget to consider non-spinal related pathologies that may cause low back pain, including:

  • Ruptured/leaking AAA:
    • Abdominal US
    • IV access, blood products as needed
    • Surgery consult
  • Pyelonephritis:
    • Physical exam with CVA tenderness and fever
    • Antibiotics, PO or IV
  • Perinephric abscess:
    • Patient with fever, malaise, vague back and abdominal pain
    • Renal US, CT with contrast
    • Antibiotics, percutaneous drainage
  • Prostatitis:
    • Patient with fever, malaise, difficulties urinating
    • DRE with very tender prostate
    • Antibiotics
  • Shingles:
    • Physical exam, history of varicella
    • Antiviral if <72 hours since onset
  • PID:
    • Sexual history
    • Pelvic exam with CMT
    • Antibiotics to cover common STIs


Disposition: Depends on underlying etiology. Those with severe, refractory pain, new debilitating neurologic conditions, hemodynamic instability, and surgical condition likely require admission.

A 45-year-old man presents to the emergency department with low back pain. The pain started about three weeks ago. He denies any known injury. Over the last week, he began experiencing some numbness in his left lower lateral leg and the top of his foot. He has been taking ibuprofen with minimal relief. He has no saddle anesthesia or incontinence. On physical examination, his vital signs are within normal limits. There is tenderness to palpation to the bilateral lumbar paraspinal musculature. He has limited range of motion with lumbar flexion and extension along with diminished sensation in the left lateral leg and dorsal foot. He also has a positive straight leg raise on the left. Based on the physical exam findings, what is the most likely lumbosacral nerve root affected?

A) L3

B) L4

C) L5

D) S1




Answer: C

L5 radiculopathy is the most common radiculopathy of the lumbosacral spine. It is often caused by a disc herniation compressing the nerve root as it exits the neural foramina. Patients will often complain of pain, numbness, or weakness. The pain typically radiates down the lateral leg. Diminished sensation is felt in the lateral leg or dorsal foot. Weakness, though not always felt by the patient, may be noted with dorsiflexion of the foot, extension of the toes, and inversion and eversion of the foot. Depression of the medial hamstring reflex may be seen as well. The medial hamstring reflex can be tested with the patient in either the prone or supine position, with your index finger over the distal, medial hamstring tendons. Tapping on your finger should cause the medial hamstring muscles to contract in a normal patient. Patients may also have a positive straight leg raise test on exam. The proper way to do this test is with the patient in a supine position. Raise the affected leg upward while keeping the knee straight. If the patient has pain radiating down the leg, that is a positive test due to traction placed on the nerve roots. Treatment may consist of nonsteroidal anti-inflammatory medications, physical therapy, epidural steroid injections, or surgery, depending on the severity of symptoms and timeline.

L3 (A) is incorrect. Irritation of the L3 nerve root results in diminished sensation of the anterolateral thigh. L4 (B) is incorrect. Irritation of the L4 nerve root results in diminished sensation of the medial leg and foot. S1 (D) is incorrect. Irritation of the S1 nerve root results in diminished sensation of the lateral and plantar foot sensation.

Rosh Review Free Qbank Access

Further Reading: 


“Acute Low Back Pain – Assessment.” Acute Low Back Pain – Assessment | Emergency Care Institute, 2017, www.aci.health.nsw.gov.au/networks/eci/clinical/clinical-resources/clinical-tools/orthopaedic-and-musculoskeletal/acute-low-back-pain/acute-low-back-pain—assessment.

Bernstein, Ian A, et al. “Low Back Pain and Sciatica: Summary of NICE Guidance.” Bmj, 2017, p. i6748., doi:10.1136/bmj.i6748.

Chou, Roger, et al. “Imaging Strategies for Low-Back Pain: Systematic Review and Meta-Analysis.” The Lancet, vol. 373, no. 9662, 2009, pp. 463–472., doi:10.1016/s0140-6736(09)60172-0.

Chou, Roger, et al. “Diagnosis and Treatment of Low Back Pain: A Joint Clinical Practice Guideline from the American College of Physicians and the American Pain Society.” Annals of Internal Medicine, vol. 147, no. 7, 2007, p. 478., doi:10.7326/0003-4819-147-7-200710020-00006.

Edlow, Jonathan A. “Managing Nontraumatic Acute Back Pain.” Annals of Emergency Medicine, vol. 66, no. 2, 2015, pp. 148–153., doi:10.1016/j.annemergmed.2014.11.011.

Helman, Anton, et al. “Low Back Pain Emergencies.” Emergency Medicine Cases, 18 Aug. 2019, emergencymedicinecases.com/episode-26-low-back-pain-emergencies/.

Inaba, Kenji, et al. “Prospective Derivation of a Clinical Decision Rule for Thoracolumbar Spine Evaluation after Blunt Trauma.” Journal of Trauma and Acute Care Surgery, vol. 78, no. 3, 2015, pp. 459–467., doi:10.1097/ta.0000000000000560.

Jarvik, Jeffrey G., and Richard A. Deyo. “Diagnostic Evaluation of Low Back Pain with Emphasis on Imaging.” Annals of Internal Medicine, vol. 137, no. 7, 2002, p. 586., doi:10.7326/0003-4819-137-7-200210010-00010.

Lin, Michelle, and Jeremiah Schuur. “A High-Value Diagnostic Approach to Low-Back Pain.” ACEP Now, 2014, www.acepnow.com/article/high-value-diagnostic-approach-low-back-pain/?singlepage=1.

Miller, Gary M., et al. “Magnetic Resonance Imaging of the Spine.” Mayo Clinic Proceedings, vol. 64, no. 8, 1989, pp. 986–1004., doi:10.1016/s0025-6196(12)61227-0.

Ropper, Allan H., and Ross D. Zafonte. “Sciatica.” New England Journal of Medicine, vol. 372, no. 13, 2015, pp. 1240–1248., doi:10.1056/nejmra1410151.

Tintinalli, Judith E., et al. Tintinalli’s Emergency Medicine a Comprehensive Study Guide. McGraw-Hill Education, 2016. pp. 1721, 1890-1894

Wang, Brandon. “Non-Traumatic Low Back Pain.” Core EM, 2017, coreem.net/core/non-traumatic-low-back-pain/.


Acknowledgements: I am a military service member. This work was prepared as part of my official duties. Title 17 U.S.C. 105 provides that “Copyright protection under this title is not available for any work of the United States Government.” Title 17 U.S.C. 101 defines a United States Government work as a work prepared by a military service member or employee of the United States Government as part of that person’s official duties.

The views expressed in this article are those of the author(s) and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government.

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