Differential Diagnosis for Back Pain

Primary Diagnostic Categories

The American College of Physicians classifies low back pain into three broad categories, with nonspecific mechanical low back pain accounting for >85% of cases, back pain with radiculopathy or spinal stenosis accounting for ~7% combined, and back pain with specific underlying pathology accounting for <2% combined 1

Cauda equina syndrome, which has a 0.04% prevalence, requires immediate MRI or CT and urgent neurosurgical consultation, and is characterized by urinary retention, fecal incontinence, saddle anesthesia, and motor deficits at multiple levels 1, 2
Vertebral malignancy, which has a 0.7% prevalence, is more likely in patients with a history of cancer, and is characterized by unexplained weight loss, age >50, and failure to improve with conservative therapy, with a positive likelihood ratio of 14.7 for a history of cancer 1, 3, 2
Vertebral compression fracture, which has a 4% prevalence, is more likely in patients with a history of osteoporosis or steroid use, and is characterized by midline tenderness in high-risk patients, with plain radiography as the appropriate initial imaging 3, 4, 2

Herniated disc with radiculopathy, which has a 4% prevalence, is characterized by sciatica with associated paraspinal muscle spasm, positive straight leg raise test, dermatomal sensory changes, and motor weakness in specific nerve root distribution, with most patients improving within 4 weeks with noninvasive management 1, 2
Spinal stenosis, which has a 3% prevalence, is characterized by pseudoclaudication, bilateral leg symptoms, and older age, with most patients improving within 4 weeks with noninvasive management 1, 2

The American College of Physicians recommends against routine imaging in patients with nonspecific low back pain without red flags, as this does not improve outcomes and may lead to unnecessary interventions, with MRI preferred over CT due to better soft tissue visualization and avoidance of radiation 1, 3, 4, 2

The American College of Physicians recommends assessing for yellow flags that predict poorer outcomes and chronic disability, including depression, passive coping strategies, job dissatisfaction, and higher disability levels, with the STarT Back tool useful for risk-stratifying patients at 2 weeks 3, 4, 2

Routine imaging for uncomplicated acute low back pain exposes patients to unnecessary radiation without clinical benefit, with a single lumbar spine x-ray equivalent to daily chest x-ray for >1 year in gonadal radiation, according to the American College of Physicians 1, 3, 4
Overlooking inflammatory causes in younger patients (<45 years) with chronic symptoms and morning stiffness delays access to highly effective TNF-blocking agents, according to the American College of Physicians 1
Failing to recognize cauda equina syndrome leads to permanent neurologic disability from delayed surgical decompression, according to the American College of Physicians 3, 4
Missing cancer in patients with prior malignancy has a posttest probability that jumps from 0.7% to 9% in this population, according to the American College of Physicians 1

The American College of Radiology recommends avoiding imaging for patients with acute lower back pain without red flags, as routine imaging provides no clinical benefit and leads to unnecessary interventions 5, 6
Disc abnormalities are present in 29-43% of asymptomatic patients depending on age, and most disc herniations show reabsorption by 8 weeks 5
Consider imaging only after 4-6 weeks of conservative management without improvement, and use MRI (preferred over CT) for better soft tissue visualization and no radiation exposure 5, 6

The American College of Internal Medicine recommends advising patients to remain active and continue ordinary activities within pain limits, as bed rest is contraindicated and leads to deconditioning and worse outcomes 7, 6
Activity as tolerated is more effective than bed rest for acute or subacute low back pain, and patients should avoid activities that worsen pain but maintain general mobility 6

The American College of Internal Medicine recommends using NSAIDs or acetaminophen as first-line treatment for acute lower back pain, as they have moderate-quality evidence for effectiveness 7
Skeletal muscle relaxants provide short-term pain relief but carry sedation and abuse risks, and opioids should be avoided initially due to equal effectiveness with NSAIDs but more adverse effects 7

Spinal manipulation by appropriately trained providers shows small to moderate short-term benefits for acute low back pain, but supervised exercise programs are not effective during the acute phase (<4 weeks) 7

Reevaluate patients at 4-6 weeks if symptoms persist, and consider imaging if patient is a potential candidate for surgery or epidural steroid injection 5, 6
For patients with spinal stenosis symptoms, MRI is indicated only if patient is surgical candidate after failed conservative therapy 6