What is the cause of radiating pain, possibly related to conditions such as sciatica, herniated disks, or spinal stenosis?

Causes of Radiating Pain

Radiating pain is caused by nerve root irritation or compression, most commonly from disc herniation, spinal stenosis, or degenerative changes that mechanically compress and chemically inflame the nerve root, producing ectopic nerve impulses perceived as pain along the nerve distribution. 1, 2

Pathophysiologic Mechanisms

The underlying cause involves both mechanical and inflammatory components working together 2:

• Mechanical compression sensitizes the nerve root to stimulation, alters nerve conduction, and compromises nutritional support through intrinsic/extrinsic vascularity and cerebrospinal fluid percolation 1, 2
• Chemical inflammation creates a non-cellular inflammatory reaction that amplifies the pain response beyond simple mass effect 1, 2
• Nerve stretching combined with compression leads to intraneural damage and functional changes in the nerve roots 2

Common Anatomical Causes

Lumbar Radiculopathy (Sciatica)

• Disc herniation is the most frequent cause, occurring in 57-65% of symptomatic patients with low back pain and radiculopathy 3
• Spinal stenosis causes nerve root compression through narrowing of the spinal canal, neural foramina, or lateral recesses 3
• Degenerative changes including facet joint hypertrophy, ligamentum flavum hypertrophy, and osteophyte formation compress nerve roots 3

Cervical Radiculopathy

• Foraminal narrowing from uncovertebral or facet joint hypertrophy compresses cervical nerve roots 3
• Disc bulging or herniation combined with degenerative spondylosis irritates cervical nerve roots 3
• Cervical radiculopathy has an annual incidence of 83.2 per 100,000 people 3

Clinical Presentation Patterns

Lumbar Radicular Pain

• Sharp, shooting, or lancinating pain felt as a narrow band down the leg, both superficially and deep 1
• Pain radiates below the knee in the sciatic nerve distribution, suggesting nerve root compromise 3, 4
• May be accompanied by dermatomal sensory changes, motor weakness, and reflex changes in specific nerve root distributions 4

Cervical Radicular Pain

• Neck pain combined with arm pain in one extremity 3
• Varying degrees of sensory or motor function loss in the affected nerve root distribution 3

Diagnostic Approach

Physical Examination Findings

The American Academy of Neurology recommends evaluating for objective neurological signs 5, 4:

• L4 nerve root: Knee strength and reflexes
• L5 nerve root: Great toe and foot dorsiflexion strength
• S1 nerve root: Foot plantarflexion and ankle reflexes

The straight leg raise test has 91% sensitivity but only 26% specificity for lumbar disc herniation 4. The crossed SLR (pain when raising the unaffected leg) has lower sensitivity (29%) but higher specificity (88%) 4.

Imaging Indications

Do not obtain routine imaging for acute radicular pain without red flags 3:

• Immediate MRI is indicated only for severe or progressive neurological deficits, cauda equina syndrome, or red flag symptoms (malignancy, infection, trauma) 3, 4
• Delayed imaging (after 4-6 weeks) is appropriate for persistent symptoms despite conservative management in surgical candidates 3, 4
• MRI lumbar spine without contrast is the preferred study, accurately depicting soft-tissue pathology, vertebral marrow, and spinal canal patency 3

Important Clinical Pitfalls

Asymptomatic Imaging Abnormalities

Disc abnormalities are common on MRI in asymptomatic patients (20-28% prevalence), so imaging findings must correlate with clinical presentation 3. Spondylotic changes are commonly identified in patients >30 years of age and correlate poorly with the presence of pain 3.

Mimicking Conditions

• Sacroiliac joint dysfunction can produce sciatica-like symptoms radiating below the buttocks, requiring MRI to differentiate from true radiculopathy 6
• Gluteal trigger points cause asymmetrical pain provoked by sitting (not standing/walking like stenosis), with normal neurological examination but tenderness on palpation of gluteus medius 5

Red Flag Symptoms Requiring Urgent Evaluation

The American College of Physicians identifies conditions requiring prompt assessment 3:

• Cauda equina syndrome (bladder/bowel dysfunction, saddle anesthesia, bilateral leg weakness)
• Progressive neurologic deficits at multiple levels
• Suspected malignancy, infection, or fracture
• Fecal incontinence or severe motor deficits