Phys · general-medicine
Undifferentiated Back Pain — A Systematic Diagnostic Approach
Also known as back pain · low back pain · lumbar pain · lumbago · non-specific back pain · mechanical back pain · undifferentiated back pain · diagnostic approach to back pain · red flag back pain · cauda equina syndrome · sciatica · radicular pain · neurogenic claudication · spinal stenosis · inflammatory back pain · ankylosing spondylitis · axial spondyloarthritis · vertebral osteomyelitis · discitis · spinal epidural abscess · osteoporotic vertebral fracture
Consultant-physician-depth guide to the systematic approach to back pain in the physician setting. Covers the triage framework (non-specific mechanical, radicular, or red-flag serious pathology); the complete differential — mechanical (musculoskeletal, disc herniation, facet joint, spinal stenosis), inflammatory (axial spondyloarthritis — ankylosing spondylitis, psoriatic and enteropathic spondylitis), infective (vertebral osteomyelitis, epidural abscess, discitis), malignant (bone metastases — breast, lung, prostate, kidney, thyroid; myeloma; primary bone tumour), metabolic (osteoporotic vertebral fracture) and referred (pancreatic cancer, AAA, renal, pelvic); the NICE NG59 red flags and cauda equina syndrome; the focused history and the systematic spine and lower-limb neurological examination (straight leg raise, femoral stretch test, per rectal); the targeted investigations (most mechanical pain needs no imaging; FBC, CRP, ESR, PSA, calcium, ALP, electrophoresis, Bence-Jones when red flags; X-ray, MRI, CT); and the management of mechanical back pain (analgesia, stay active, physiotherapy, CBT, multidisciplinary pain programme). Structured for FRACP DWE and DCE preparation.
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Red flags
- Back pain with saddle anaesthesia, urinary retention or incontinence, faecal incontinence, or bilateral leg symptoms is cauda equina syndrome — emergency MRI within 24 hours and urgent surgical decompression; a post-void residual and a per rectal examination are mandatory and must not be omitted
- A known cancer patient with new or worsening back pain has malignant spinal cord compression until proven otherwise — give dexamethasone 16 mg and image urgently; do not wait for the neurological deficit, because back pain precedes the deficit in over 95 per cent of cases
- Back pain with fever, or in an intravenous drug user, or in an immunocompromised host, is vertebral osteomyelitis or epidural abscess until proven otherwise — the X-ray can be normal for weeks; check CRP and ESR and image with MRI
- Night pain that does not settle with rest is a red flag for malignancy, infection or inflammation — mechanical pain typically settles at rest
- A sudden severe back pain in a postmenopausal woman or a chronic corticosteroid user on minimal trauma is an osteoporotic vertebral fracture until proven otherwise
- A tearing back pain in an older man with a pulsatile abdominal mass is a ruptured abdominal aortic aneurysm — call for surgical and vascular help before any imaging; mortality exceeds 80 per cent
- Deep boring upper abdominal or back pain with weight loss and painless jaundice is pancreatic cancer until proven otherwise
Undifferentiated Back Pain — A Systematic Diagnostic Approach
The answer first
Back pain is one of the commonest presentations in general medicine — the lifetime prevalence is over 80 per cent, and it is the leading global cause of years lived with disability. The registrar's task is not to "diagnose" the back pain in most patients — it is to triage the patient. The triage sorts every back pain patient into one of three bins, and each bin has a different management logic: [1]
- Non-specific (mechanical) back pain — about 90 per cent of cases. The pain is reproduced by mechanical load and relieved by rest. There are no red flags, no neurological deficit, and no systemic symptoms. Management is reassurance, education, staying active and simple analgesia. No imaging is needed.
- Radicular (nerve root) pain — back pain radiating below the knee in a dermatomal distribution, with or without a neurological deficit. The common cause is a lumbar disc herniation compressing a nerve root. Most settle with conservative therapy; the minority need imaging and, rarely, surgery.
- Back pain with red flags — the minority that harbour serious pathology: fracture, infection, malignancy, inflammatory disease, or cord or cauda equina compromise. These need targeted investigation and urgent, cause-specific management. [1]
The reproducible sequence for any back pain patient is: [1]
- Screen for the emergency first — cauda equina syndrome, cord compression, a ruptured AAA. Ask about saddle anaesthesia, bladder and bowel function, and palpate the abdomen. These cannot wait.
- Take the red flag history — age, cancer, weight loss, night pain, fever, steroids, intravenous drug use, immunocompromise, trauma, a progressive neurological deficit.
- Triage — mechanical, radicular, or red-flag, by the history and the examination.
- Investigate the red flags only — most mechanical pain needs no imaging; the red flags drive the bloods and the MRI.
- Manage the cause — reassure and mobilise the mechanical patient; investigate and treat the serious pathology. [1]
The single most dangerous error is assuming the pain is mechanical without screening for the red flags. The cauda equina syndrome missed because the registrar did not ask about urinary function or perform a per rectal examination; the vertebral osteomyelitis called "muscular pain" in the intravenous drug user; the pancreatic cancer presenting as "upper back pain" for three months — these are the misses that define a poor physician. The second error is over-investigating the mechanical patient — the MRI that reveals an age-related disc bulge in an asymptomatic person, the cascade of referrals and injections and surgery that follows, none of which improves the outcome. [1]
Viva trap: "What is the first question you ask a patient with back pain?" The honest answer is "Tell me about your bladder and your bowels." The triage of back pain begins with the cauda equina screen, because cauda equina syndrome is the time-critical emergency that is missed if the registrar reaches for the musculoskeletal history first. The registrar who screens for cauda equina in the first minute of every back pain encounter has organised the entire assessment. [1]
References8ShowHide
- [1]Deyo RA, Weinstein JN Low back pain N Engl J Med, 2001.PMID 11172169
- [2]Koes BW, van Tulder MW, Thomas S Diagnosis and treatment of low back pain BMJ, 2006.PMID 16777886
- [3]Qaseem A, Wilt TJ, McLean RM, et al. Noninvasive Treatments for Acute, Subacute, and Chronic Low Back Pain: A Clinical Practice Guideline From the American College of Physicians Ann Intern Med, 2017.PMID 28192789
- [4]Foster NE, Anema JR, Cherkin D, et al. Prevention and treatment of low back pain: evidence, challenges, and promising directions Lancet, 2018.PMID 29573872
- [5]Lavy C, James A, Wilson-MacDonald J, Fairbank J Cauda equina syndrome BMJ, 2009.PMID 19336488
- [6]Darouiche RO Spinal epidural abscess N Engl J Med, 2006.PMID 17093252
- [7]Mylona E, Samarkos M, Kakalou E, Fanourgiakis P, Skoutelis A Pyogenic vertebral osteomyelitis: a systematic review of clinical characteristics Semin Arthritis Rheum, 2009.PMID 18550153
- [8]Rudwaleit M, van der Heijde D, Landewé R, et al. The development of Assessment of SpondyloArthritis international Society classification criteria for axial spondyloarthritis (part II): validation and final selection Ann Rheum Dis, 2009.PMID 19297344