What red‑flag features in back pain warrant urgent evaluation and imaging?

Red Flags of Back Pain Requiring Urgent Evaluation

Red flags in back pain are clinical features that significantly increase the probability of serious underlying pathology—including malignancy, infection, fracture, or neurological compromise—and mandate immediate imaging and further investigation. 1

Critical Red Flags on History

• History of cancer is the single most important red flag, increasing the probability of spinal malignancy from 0.7% to 9% 2
• Age ≥ 65 years markedly raises fracture risk and alone justifies immediate imaging after trauma 2
• Recent significant trauma (fall from height ≥ 10 feet, motor vehicle crash > 50 mph) warrants urgent evaluation for vertebral fracture 2
• Constant pain, night pain, or radicular pain lasting ≥ 4 weeks constitute red flags requiring advanced imaging 1
• Progressive neurological deficits (motor weakness, sensory changes, bowel/bladder dysfunction) confer a 10-fold increased risk of serious pathology and demand urgent intervention 1, 2
• Fever with back pain suggests spinal infection (discitis, osteomyelitis, epidural abscess) 1
• Unintentional weight loss raises concern for malignancy 1
• Intravenous drug use or indwelling vascular catheter significantly increases risk of epidural abscess 3
• Chronic steroid use or known osteoporosis creates high vulnerability to compression fractures even after minor trauma 2
• Anticoagulation therapy increases risk of epidural hematoma and fracture complications 2

Critical Red Flags on Physical Examination

• Neurological deficits including motor weakness, sensory changes, asymmetric reflexes, or abnormal rectal tone suggest nerve root compression or spinal cord involvement 1
• Gait abnormalities indicate neurological involvement or mechanical instability 1
• Palpable mass in the lumbar region mandates immediate MRI with and without contrast to exclude tumor, abscess, or hematoma 1
• Abnormal spinal curvature or alignment may indicate structural pathology or fracture 1
• Focal tenderness over spinous processes after trauma suggests fracture 2
• Inability to bear weight or ambulate is a red flag requiring immediate imaging 2
• Tachycardia may indicate systemic infection or inflammatory process 1
• Palpable lymphadenopathy suggests malignancy or infection 1
• Limited range of motion with morning stiffness suggests inflammatory conditions such as spondyloarthropathy 1

Imaging Algorithm Based on Red Flags

First-Line Imaging

• Plain radiographs (AP and lateral views) of the symptomatic region are the appropriate first-line study when red flags are present 1, 2
• Critical caveat: Negative radiographs do not exclude serious pathology; at least 50% bone loss must occur before changes become visible on standard films 2
• Radiographs can identify fractures, lytic or sclerotic lesions, alignment abnormalities, and some primary bone tumors 4, 2

When to Proceed Directly to Advanced Imaging

• MRI without and with IV contrast of the complete spine is the definitive study when infection, malignancy, or inflammatory disease is suspected based on clinical presentation or laboratory findings 4, 1
• MRI is the only modality that directly visualizes the spinal cord, ligaments, intervertebral discs, and paraspinal soft tissues 4
• Urgent MRI without contrast is required for suspected cauda equina syndrome or progressive neurological deficits 1
• Pre-contrast sequences must be obtained before administering gadolinium to accurately interpret enhancement patterns 4
• Fat-suppressed T2 and T1 post-contrast sequences (STIR, Dixon, fat-suppressed turbo spin echo) are essential for detecting marrow edema, infection, and neoplastic disease 4

Alternative Imaging When MRI Is Contraindicated

• CT with IV contrast targeted to the area of interest is reserved for patients who cannot undergo MRI 4
• CT provides excellent bone detail and can detect paraspinal abscesses but is inferior to MRI for soft-tissue characterization 4
• Tc-99m bone scan with SPECT may be appropriate for suspected spondylolysis or multifocal osseous pathology but does not adequately assess intraspinal or paraspinal soft-tissue disease 4

Special Populations: Pediatric Red Flags

• Any back pain in a child < 5 years old is a red flag requiring immediate evaluation 5
• Constant pain in a pediatric patient mandates imaging with plain radiographs followed by MRI if radiographs are negative or clinical suspicion remains high 5
• Nighttime symptoms (pain, vomiting) are highly concerning for spinal neoplasm, which presents with persistent nighttime pain in 25–30% of pediatric cases 5
• Normal spine radiographs in children do not exclude serious pathology; MRI with and without contrast of the complete spine should be obtained when red flags persist 5

Common Pitfalls and Caveats

• Do not rely on the absence of red flags to exclude serious pathology: 64% of patients with spinal malignancy had no associated red flags in one large cohort 6
• Night pain alone is a poor discriminator: For patients without fever or recent infection, night pain was a false positive for infection > 96% of the time 6
• Do not skip imaging in patients ≥ 65 years after even "minor" falls; age alone justifies radiography due to high fracture risk 2
• Do not obtain oblique lumbar views; they double radiation exposure without adding diagnostic value 2
• Do not delay advanced imaging for a trial of conservative therapy when red flags are present 1, 2
• Do not order MRI with contrast alone; pre-contrast sequences are required for proper interpretation 4
• The prevalence of serious spinal pathology in emergency department settings (2.5–7.4%) is substantially higher than in primary care (< 1%), so maintain a lower threshold for imaging in acute presentations 3

When Imaging Is Not Indicated

• MRI, CT, and bone scans are not indicated for back pain without clinical red flags 4
• More than 85% of primary care patients have nonspecific low back pain that resolves within 4–6 weeks with conservative management 2
• Routine laboratory tests are not recommended for nonspecific low back pain without red flags 2