back pain differential

Tiny Tip: Back Pain Differential Mnemonic

In Medical Concepts, Tiny Tips by Carly RumleyLeave a Comment

Back pain is a common presentation to the Emergency Department. It is associated with disability, health care expenses, and a loss of wages and productivity. When caring for a patient and developing a back pain differential diagnosis, remember to consider age, the history, physical exam findings, laboratory results, and imaging (if needed). Be sure to keep in mind the red flags for back pain that include: history of IV drug use, history of cancer, night time symptoms, fever, saddle anesthesia, bowel or bladder incontinence, or neurologic symptoms such as weakness or asymmetric reflexes. Certain red flags (saddle anesthesia, bowel/bladder incontinence, neurologic symptoms) can indicate cauda equina syndrome. This syndrome is not specifically listed here, as it has many causes listed below: Tumour, trauma, spinal stenosis, etc.1,2

As back pain is no minor complaint, the mnemonic “T(he) MMIINNORR” can be used to organize your back pain differential diagnosis and to prompt you to consider these different causes.

Trauma

Depending on the history of trauma, the back or neck should be immobilized pending imaging results. Vertebral fractures are more likely in patients with osteoporosis, glucocorticoid use, osteomyelitis, or neoplasm. Trauma commonly results in:

  • Fractures – the spinal cord is at risk for compression with fractures above L1.
  • Herniated disc

Mechanical

This is the most common cause of back pain in the emergency department. While a benign condition, mechanical back pain can be exceptionally painful, warranting a visit to the Emergency Department. It is typically the result of poor posture and/or incorrect bending or lifting motions. When evaluating a patient with mechanical back pain one must rule out the more sinister causes of back pain that arise in this mnemonic.

Metabolic

Metabolic diseases such as osteoporosis and osteosclerosis put patients at higher risk of several causes of back pain such as compression fractures.

Inflammatory

Patients with back pain associated with weight loss, systemic symptoms, and/or other joint involvement are more likely to have an inflammatory cause. The hallmark symptom is morning stiffness and the pain often improves with activity. Pay special attention to the sacroiliac joints on exam because this is often the site of inflammation.

  • Ankylosing Spondylitis
  • Inflammatory Bowel Disease
  • Psoriatic arthritis
  • Rheumatoid arthritis
  • Reactive arthritis (ex. chlamydia)

Infection

Patients with a history of IV drug use, diabetes mellitus, recent spine surgeries or procedures (ex. SI joint injections), or patients with fevers and infections at another source (ex. pneumonia, UTI, skin infection) are at risk. Clues for infectious causes of back pain are pain unrelieved by rest, spine tenderness over involved area, elevated ESR/CRP, fever, and elevated WBC count.

  • Vertebral osteomyelitis
  • Spinal epidural abscess
  • Discitis
  • Meningitis
  • Lumbar arachnoiditis

Neurologic

Patients with symptoms such as shooting pain radiating to the lower legs and weakness likely have a neurologic causes of back pain.

  • Radiculopathy/nerve root injury – this neurological cause of pain can be caused by anything that can impinge the nerve, including disc bulge, disc herniation, or in rare cases, a growing mass lesion.
  • Spinal stenosis

Neoplasms

With a neoplastic cause of back pain, the pain is usually constant, dull, and worse at night. Weight loss, night sweats, and history of cancer can also indicate a neoplastic cause.

  • Metastatic disease (ex. prostate cancer) 
  • Hematologic (ex. multiple myeloma)
  • Primary bone tumours

Other

Other causes of back pain to consider are:

  • Degenerative: osteoarthritis / spondylosis
  • Chronic pain syndrome
  • Conversion disorder
  • Malingering
  • Developmental – Most of the time this will not present for the first time in the emergency department but it can be a contributing factor to those presenting with pain.
  • Spondylolysis
  • Kyphoscoliosis
  • Spina bifida occulta
  • Tethered spinal cord

Ruptured abdominal aortic aneurysm

This is a cause of back pain that must be ruled out, especially in acute ED presentations. The classic presentation includes abdominal pain and shock, in addition to back pain. A typical patient with a ruptured AAA would be elderly, male, with a history of smoking. A pulsatile mass may be palpable on abdominal exam or (better yet!) ultrasound.

Referred pain

Pain from a visceral disease can manifest as back pain.

  • Ruptured abdominal aortic aneurysm (as discussed above)
  • Abdominal aortic dissection
  • Renal colic
  • Diseases of the thorax (ex. pneumonia), abdomen (ex. renal colic), or pelvis (ex. UTI)
  • Gynecologic disorders involving the uterosacral ligaments (ex. endometriosis, uterine cancers)

This post was copy edited by Taylor Nikel and peer reviewed by Ryan Chadwick.

References:

1.
Stone C Keith, Humphries R. CURRENT Diagnosis and Treatment Emergency Medicine, Seventh Edition, Chapter 21. McGraw Hill Professional; 2011.
2.
Kasper D, Jameson J Larry, Hauser S, Loscalzo J, Fauci A, Longo D. Harrison’s Principles of Internal Medicine 19/E (Vol.1 & Vol.2) Chapter 22. McGraw-Hill Education / Medical; 2015.

Reviewing with the Staff

The above mnemonic provides a reasonable differential for back pain. It may be helpful to junior learners who want to ensure that they consider numerous causes of back pain and present them to their attending in an organized fashion. When doing so, it is important to also consider the likelihood of each presentation and, unless conducting an exercise in coming up with all potential differentials, prioritize them based on it and the potential danger to the patient. For example, in a young and otherwise healthy patient with no red flag symptoms mechanical back pain should come up much earlier in the differential than the causes listed under referred pain. Advanced learners should be able to come up with these categorical clusters without a mnemonic, but this approach might be important to think through deliberately in atypical cases.

Brent Thoma
Brent Thoma is an emergency physician who works at the University of Saskatchewan College of Medicine.

Staff Edits and Mentor

Dr. Brandy Stauffer
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Carly Rumley

Carly Rumley

Carly is a fourth year medical student at the University of Alberta.
Carly Rumley

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