Low Back Pain
One of the most common reasons adults see a doctor, and one of the most over-imaged. The entire skill is separating the 90-95% with nonspecific pain that improves on its own from the few percent with a red-flag cause, then resisting the scan that will find degenerative changes present in most asymptomatic adults. Cauda equina and spinal infection are the misses that end careers and mobility.
🔍 Overview
Three Categories, and Only One Is Common
- Nonspecific mechanical low back pain -roughly 90-95% of presentations. No identifiable structural cause, no imaging correlate, and most improve substantially within 4-6 weeks regardless of what is prescribed. Naming it as a specific diagnosis rather than "nothing found" matters for how the patient hears the plan.
- Radicular pain / lumbosacral radiculopathy -a small minority. Nerve-root compression producing pain radiating below the knee in a dermatomal pattern, often with numbness or weakness. Most disc herniations also resolve without surgery.
- Serious specific pathology -a few percent. Malignancy, infection, fracture, cauda equina syndrome, inflammatory spondyloarthritis, and non-spinal causes referred to the back. This is the group the history and exam exist to find.
History That Actually Discriminates
- Duration and course: acute (< 4 weeks), subacute (4-12), chronic (> 12). Most acute pain improves; pain that is progressive and unremitting, or worse at night and at rest, is the pattern that worries.
- Radiation below the knee suggests radiculopathy; pain confined to the back and buttocks usually does not.
- Inflammatory features -age under 45, insidious onset, morning stiffness over 30 minutes, improvement WITH exercise and NOT with rest, night pain in the second half of the night, good response to NSAIDs. This inverted pattern is the tell for axial spondyloarthritis, and it is routinely missed for years.
- Neurogenic claudication -bilateral leg pain and heaviness with walking or standing, relieved by sitting or leaning forward (the shopping-cart sign), suggesting lumbar spinal stenosis. Contrast with vascular claudication, which is relieved by standing still.
- Ask about function and yellow flags -fear-avoidance beliefs, catastrophizing, depression, job dissatisfaction and pending litigation predict chronicity better than any imaging finding, and they are modifiable.
🚨 Red Flags
Cauda equina syndrome is the emergency. New urinary retention (the most consistent finding), overflow incontinence, saddle anesthesia, bilateral leg weakness or sciatica, and loss of anal sphincter tone. Suspicion warrants urgent MRI and immediate surgical consultation, not an outpatient referral, because delayed decompression converts a recoverable syndrome into permanent bladder, bowel and sexual dysfunction. A post-void residual is the fastest bedside test -a significantly elevated PVR in a patient with back pain and leg symptoms is the finding that stops everything else.
The Rest of the Red Flags, by Cause
| Suspected cause | Red flags | Action |
|---|---|---|
| Malignancy | History of cancer (the strongest single predictor), unexplained weight loss, age over 50, pain worse at night or at rest, no improvement after 4-6 weeks | Imaging plus ESR/CRP; MRI if suspicion is meaningful. Breast, prostate, lung, kidney and thyroid metastasize to bone. |
| Spinal infection (osteomyelitis, discitis, epidural abscess) | Fever, injection drug use, recent bacteremia or endocarditis, indwelling catheters or lines, immunosuppression, recent spinal procedure, unremitting night pain, focal spinal tenderness | MRI with contrast plus blood cultures, ESR and CRP. Do not start antibiotics before cultures unless septic. Epidural abscess can progress to paralysis over hours. |
| Vertebral fracture | Age over 70, significant trauma (or minor trauma with osteoporosis), prolonged glucocorticoid use, known osteoporosis, sudden severe focal pain | Plain radiographs first; CT or MRI if films are negative and suspicion persists. Links to the osteoporosis topic -a fragility fracture is a treatment indication. |
| Cauda equina / severe neuro deficit | Retention, saddle anesthesia, bilateral deficits, progressive motor weakness | Emergency MRI and surgical consult. |
| Axial spondyloarthritis | Under 45, insidious onset, morning stiffness over 30 min, better with exercise, worse with rest, night pain, alternating buttock pain, psoriasis, IBD, uveitis | ESR/CRP, HLA-B27, MRI of the sacroiliac joints (which shows sacroiliitis years before plain films), rheumatology referral. |
Non-Spinal Causes That Present as Back Pain
- Abdominal aortic aneurysm -older patient, vascular risk factors, tearing pain, pulsatile mass. A rupture presenting as "back pain" is a classic fatal miss.
- Nephrolithiasis and pyelonephritis -flank pain, hematuria, fever, costovertebral tenderness.
- Pancreatitis, aortic dissection, retroperitoneal pathology, and pelvic disease including endometriosis.
- Herpes zoster before the rash appears -dermatomal burning pain without mechanical features.
🧪 Imaging
Do Not Image Acute Nonspecific Back Pain
- No imaging in the first 6 weeks for nonspecific low back pain without red flags -this is one of the strongest and most consistently repeated recommendations in ambulatory medicine (ACP guidance and the Choosing Wisely campaign both lead with it).
- Why: imaging does not improve pain, function or outcomes in this group; it exposes patients to radiation and cost, and it reliably finds incidental degenerative changes that are present in a large majority of asymptomatic adults -disc degeneration, bulges, and facet arthropathy rise steadily with age in people who have no pain at all.
- The harm is not just wasted money. Early imaging is associated with worse outcomes: it medicalizes a self-limited problem, anchors the patient to a structural explanation, increases fear-avoidance, and leads to more procedures and surgery without better function.
When Imaging Is Indicated
- Any red flag for cancer, infection, fracture or cauda equina -image promptly and choose the modality by the question: MRI for suspected infection, malignancy, cauda equina and radiculopathy; plain films first for suspected fracture.
- Persistent pain beyond 4-6 weeks of appropriate conservative care, especially with radicular features.
- Progressive or severe neurologic deficit, or when a surgical or interventional procedure is genuinely being considered -imaging should be ordered to answer a management question, not to explain the pain.
- Report language matters: when imaging is obtained, frame incidental degenerative findings as age-expected and common in pain-free people, in the same breath as the result. Unframed, those words become the patient's diagnosis for years.
💊 Management
Acute and Subacute Pain (nonpharmacologic first)
- Reassure with a specific prognosis and stay active -most improve substantially within weeks, and bed rest delays recovery. "Keep moving, resume normal activity as tolerated" is an evidence-based prescription, not a platitude.
- First-line is nonpharmacologic: superficial heat, massage, acupuncture, or spinal manipulation, per current ACP guidance -medication is second-line for acute pain.
- If drugs are used: NSAIDs first, at the lowest effective dose, with the usual GI, renal and cardiovascular caveats. Skeletal muscle relaxants can help short-term but sedate; use briefly and cautiously in older adults.
- Acetaminophen is not effective for acute low back pain in the better trials, which surprises most people who reach for it first.
- Do not prescribe opioids routinely -reserve for severe pain unresponsive to everything else, at the lowest dose for the shortest duration, with an explicit stop plan. Systemic glucocorticoids do not help nonspecific low back pain or acute radiculopathy meaningfully.
Chronic Low Back Pain (> 12 weeks)
- Exercise therapy is the backbone -no single modality is clearly superior, so the sustainable one wins. Add multidisciplinary rehabilitation, cognitive behavioral therapy, mindfulness-based stress reduction, tai chi or yoga, all of which have supporting evidence.
- Address the yellow flags directly: fear-avoidance, catastrophizing and depression drive disability more than structural findings do, and treating them changes outcomes.
- Pharmacologic options are adjuncts: NSAIDs first-line; duloxetine has evidence in chronic low back pain; tricyclics are weaker than once believed. Gabapentinoids do not work for nonspecific low back pain or sciatica -a common, unhelpful prescription.
- Interventional and surgical care is narrow: epidural steroid injection can give short-term relief for radicular pain but does not change long-term outcomes or surgery rates; surgery is for persistent radiculopathy with correlating imaging, progressive deficits, or symptomatic stenosis, and fusion for nonspecific back pain has poor evidence.
Radiculopathy and Stenosis Specifics
- Most lumbar disc herniations improve without surgery, often with radiographic regression of the herniation itself -so the default is 6 weeks of conservative care unless deficits are progressive.
- Early surgery for sciatica speeds relief but does not improve outcomes at one to two years versus conservative care, which makes the decision a patient-preference conversation about how fast versus how invasive.
- Spinal stenosis -conservative care and PT first; decompression is reasonable for persistent, function-limiting neurogenic claudication. Symptoms and function drive the decision, not the canal diameter.
🏥 Rounds
Pimp Questions
❓ What is the earliest and most consistent finding in cauda equina syndrome, and what is the fastest bedside test?
Urinary retention is the most consistent finding -saddle anesthesia and bilateral leg symptoms are classic but less reliably present early, and waiting for the full syndrome is how the diagnosis gets missed. The fastest bedside test is a post-void residual (bladder scan or catheter): a significantly elevated PVR in a patient with back pain and leg symptoms should stop the visit and trigger urgent MRI plus immediate surgical consultation. Delay converts a recoverable syndrome into permanent bladder, bowel and sexual dysfunction, which is why this is a same-hour problem rather than a referral.
❓ Why is early imaging for nonspecific acute low back pain actively harmful rather than merely unnecessary?
Because it changes the patient's model of their illness. Degenerative disc disease, bulges and facet arthropathy are present in a large majority of asymptomatic adults and rise with age, so a scan in acute back pain will nearly always find something. Reported without framing, those findings anchor the patient to a structural explanation, increase fear-avoidance, and are associated with more procedures, more surgery and worse functional outcomes -not just extra cost and radiation. Hence the ACP and Choosing Wisely recommendation against imaging in the first 6 weeks absent red flags.
❓ A 32-year-old has 8 months of back pain with 45 minutes of morning stiffness that improves when he plays soccer and worsens when he sits at his desk. What does the pattern suggest?
Inflammatory back pain -axial spondyloarthritis until proven otherwise. The discriminating feature is the inverted pattern: better with exercise, worse with rest, the opposite of mechanical pain. Supporting features are age under 45, insidious onset, morning stiffness over 30 minutes, second-half-of-night pain, alternating buttock pain, and a good NSAID response. Work up with ESR/CRP, HLA-B27 and MRI of the sacroiliac joints, which detects sacroiliitis years before plain films, then refer. Ask about psoriasis, inflammatory bowel disease and uveitis, since these travel together.
❓ How do you distinguish neurogenic from vascular claudication at the bedside?
By what relieves it and by posture. Neurogenic claudication (lumbar spinal stenosis) is relieved by sitting or leaning forward -flexion opens the canal, hence the "shopping-cart sign" and the ability to cycle further than they can walk. Vascular claudication is relieved by standing still, regardless of posture, since it is a demand-supply problem, and it comes with diminished pulses, hair loss and an abnormal ABI. Walking uphill is easier in neurogenic (more flexion) and harder in vascular (more demand).
❓ Which commonly prescribed drugs do NOT work for low back pain?
Three worth knowing. Acetaminophen is ineffective for acute low back pain in the better trials despite being the reflex first choice. Gabapentinoids do not work for nonspecific low back pain or sciatica, and carry sedation, edema and misuse potential. Systemic glucocorticoids do not meaningfully help nonspecific back pain or acute radiculopathy. Add that opioids should not be routine, and that the effective interventions here are largely nonpharmacologic: staying active, heat, exercise therapy, and addressing fear-avoidance.
Sample Presentation
Mr. Whitfield is a 44-year-old warehouse worker with 5 days of low back pain after lifting, without radiation below the knee. No fever, no weight loss, no cancer history, no trauma, no bladder or bowel change. Exam: paraspinal tenderness, painful but full range, normal strength, sensation and reflexes, negative straight-leg raise. He is anxious that he has "slipped a disc" and asks for an MRI, and mentions he is worried about losing his job if this continues.
Key Points: (1) Nonspecific acute low back pain with no red flags -no imaging, and saying why matters: a scan would very likely show degenerative changes that are present in most pain-free adults his age, and early imaging is associated with worse outcomes, not better ones. (2) The prescription is stay active, avoid bed rest, superficial heat, and an NSAID at the lowest effective dose, with a specific prognosis (most improve substantially within weeks) rather than vague reassurance. (3) The job-loss worry is a yellow flag and predicts chronicity more strongly than anything on his exam -address it directly, discuss modified duties, and arrange follow-up at 4-6 weeks with explicit return precautions for new leg weakness, numbness in the saddle area, or trouble urinating.
Clinic Checklist
- Cauda equina screened by history every time: urinary retention, saddle numbness, bilateral leg symptoms, new incontinence -PVR if any doubt.
- Red flags for cancer, infection and fracture asked explicitly (cancer history, fever, IV drug use, steroids, osteoporosis, trauma, weight loss, night pain).
- Inflammatory pattern considered in the under-45 patient -better with exercise, worse with rest.
- Non-spinal mimics considered: AAA in the older vasculopath, renal colic, pyelonephritis, zoster.
- No imaging in the first 6 weeks without a red flag -and if imaging is done, incidental degenerative findings are framed as age-expected at the time of disclosure.
- Stay-active advice given explicitly, bed rest discouraged, nonpharmacologic therapy offered first.
- Yellow flags addressed: fear-avoidance, catastrophizing, mood, work situation.
- Return precautions documented and follow-up arranged at 4-6 weeks if not improving.
📋 Summary
Summary
Ninety Percent Is Nonspecific
Roughly 90-95% of low back pain has no identifiable structural cause and improves substantially within weeks, a few percent has serious pathology, and a small minority is true radiculopathy (pain below the knee in a dermatomal pattern). The whole clinical skill is sorting those groups with history and exam rather than with a scanner.
Cauda Equina Is the Emergency
New urinary retention is the most consistent early finding -saddle anesthesia, bilateral leg symptoms and lost sphincter tone are classic but later. A post-void residual is the fastest bedside test, and suspicion means urgent MRI plus immediate surgical consultation, not an outpatient referral, because delay converts a recoverable syndrome into permanent bladder, bowel and sexual dysfunction.
Ask the Red-Flag Questions Every Time
Cancer history is the strongest single predictor of malignancy; add weight loss, age over 50 and night pain. Infection: fever, injection drug use, recent bacteremia, indwelling lines, immunosuppression, recent spinal procedure -MRI with contrast plus blood cultures, because epidural abscess can progress to paralysis over hours. Fracture: age over 70, trauma (or minor trauma with osteoporosis), chronic steroids.
The Inverted Pattern Means Inflammation
Under 45, insidious onset, morning stiffness over 30 minutes, better WITH exercise and worse WITH rest, night pain in the second half of the night -that is axial spondyloarthritis, and it is routinely missed for years because it is filed as mechanical pain. Work it up with ESR/CRP, HLA-B27 and MRI of the sacroiliac joints, which shows sacroiliitis long before plain films.
Do Not Image the First Six Weeks
No imaging for nonspecific acute low back pain without red flags -one of the strongest recommendations in ambulatory medicine. Degenerative changes are present in a large majority of asymptomatic adults, so a scan almost always finds something, and early imaging is associated with more procedures, more surgery and worse function, not better outcomes. When imaging is done, frame incidental findings as age-expected at the moment you report them.
Stay Active, and Say So Specifically
Bed rest delays recovery. Reassure with a real prognosis and prescribe activity, with nonpharmacologic therapy first (heat, massage, acupuncture, manipulation). NSAIDs are the first-line drug; muscle relaxants help briefly but sedate. Acetaminophen is ineffective for acute low back pain, systemic steroids do not help, and opioids are not routine.
Chronic Pain Is a Function Problem
Exercise therapy is the backbone and the sustainable modality wins, supported by multidisciplinary rehabilitation, CBT, mindfulness, tai chi and yoga. Yellow flags -fear-avoidance, catastrophizing, depression, job dissatisfaction- predict disability better than any imaging finding and are modifiable, so they belong in the plan. Duloxetine has evidence; gabapentinoids do not work for back pain or sciatica.
Surgery Is Narrow, and Time Is on Your Side
Most disc herniations improve without surgery, often with radiographic regression, so 6 weeks of conservative care is the default absent progressive deficits. Early surgery for sciatica speeds relief but does not improve one-to-two-year outcomes, making it a preference conversation. Decompression is reasonable for function-limiting neurogenic claudication; fusion for nonspecific back pain has poor evidence, and epidural steroids give short-term radicular relief without changing the long game.
