Definition and epidemiology
Sciatica is a clinical syndrome, not a diagnosis in itself, defined by pain that radiates along the course of the sciatic nerve (L4-S1 nerve roots) from the buttock down the posterior or posterolateral thigh and leg, often below the knee. It results from irritation, compression, or inflammation of one or more lumbosacral nerve roots.
- Lifetime prevalence is approximately 10-40%, with annual incidence around 1-5%
- Peak incidence occurs between ages 30 and 50
- Men and women are affected roughly equally, though some studies show slight male predominance
- Risk increases with occupations involving heavy lifting, prolonged sitting, or vibration exposure (e.g., truck driving)
Most cases are self-limited, with the majority improving within 4-6 weeks regardless of specific treatment.
- Pain radiating below the knee is more specific for radiculopathy than axial back pain alone
- L4-L5 and L5-S1 are the most common levels of disc herniation causing sciatica
- Positive straight-leg raise (30-70 degrees) suggests nerve root tension; crossed SLR is more specific
- Cauda equina syndrome (saddle anesthesia, bowel/bladder dysfunction) is a surgical emergency
- MRI is the imaging modality of choice but is not needed in the first 4-6 weeks without red flags
- First-line treatment is conservative: NSAIDs, activity, physical therapy, not bed rest
- Epidural steroid injections give short-term relief but do not change long-term surgical outcomes
- Piriformis syndrome mimics sciatica but originates outside the spinal canal
Etiology and risk factors
The most common cause is lumbar disc herniation compressing an adjacent nerve root, accounting for the majority of cases in younger and middle-aged adults.
Common causes
- Lumbar disc herniation (most common, especially L4-L5 and L5-S1 levels)
- Lumbar spinal stenosis (more common in older adults, often bilateral and positional)
- Spondylolisthesis
- Facet joint hypertrophy or osteophyte formation
- Piriformis syndrome (nerve compression outside the spinal canal, a key differential)
Less common causes
- Spinal tumors (primary or metastatic)
- Epidural abscess or hematoma
- Pregnancy (mechanical and hormonal factors)
Risk factors
- Age 30-50 years
- Obesity
- Sedentary lifestyle or prolonged sitting
- Occupations requiring heavy lifting, twisting, or whole-body vibration
- Smoking (associated with accelerated disc degeneration)
- Prior history of low back pain
Pathophysiology
Nerve root irritation in sciatica arises from a combination of mechanical compression and chemical inflammation.
- Mechanical compression: A herniated nucleus pulposus (most often postero-lateral) impinges on the traversing nerve root as it exits the spinal canal, or stenotic changes narrow the lateral recess or neural foramen
- Chemical/inflammatory component: Herniated disc material releases inflammatory mediators (including tumor necrosis factor-alpha and interleukins) that sensitize the nerve root, explaining why pain severity does not always correlate with the degree of mechanical compression
- Nerve root level correlation:
| Level | Herniation site | Motor finding | Sensory finding | Reflex |
|---|---|---|---|---|
| L4 | L3-L4 disc | Knee extension weakness | Medial leg/ankle | Patellar reflex reduced |
| L5 | L4-L5 disc | Foot/toe dorsiflexion weakness | Dorsum of foot, big toe | No reliable reflex |
| S1 | L5-S1 disc | Plantarflexion weakness | Lateral foot, sole | Ankle (Achilles) reflex reduced |
Chronic or severe compression can lead to demyelination and, in severe cases, axonal loss, which correlates with persistent motor deficits.
Clinical features
Patients typically describe unilateral pain radiating from the lower back or buttock down the leg, often described as sharp, burning, or electric-shock-like, worse with sitting, bending, coughing, or sneezing (Valsalva maneuver increases intrathecal pressure).
Key symptoms
- Pain radiating below the knee (more specific for radiculopathy than back pain alone)
- Numbness or tingling in a dermatomal distribution
- Weakness in the affected myotome
- Pain often worse with sitting, better with lying supine with knees flexed
Red flag symptoms (require urgent evaluation)
- Saddle anesthesia
- New bowel or bladder dysfunction (incontinence or retention)
- Bilateral leg weakness
- Progressive or severe neurologic deficit
These suggest cauda equina syndrome, a surgical emergency.
Physical examination
- Straight-leg raise test: passive leg raised with knee extended; pain reproduced between 30-70 degrees suggests L4-S1 nerve root tension (sensitive but not highly specific)
- Crossed straight-leg raise: pain in the affected leg when raising the contralateral leg; less sensitive but more specific
- Dermatomal sensory testing and myotomal strength testing to localize the level
- Deep tendon reflexes (patellar for L4, Achilles for S1)
Diagnosis
Sciatica is primarily a clinical diagnosis based on history and examination. Imaging is not routinely needed in the first 4-6 weeks unless red flags are present.
When to image
- Red flag features (cauda equina, infection, malignancy suspicion, trauma)
- Progressive neurologic deficit
- Failure to improve after 4-6 weeks of conservative therapy
- Consideration of surgery or interventional procedures
Imaging modalities
- MRI lumbar spine (without contrast): modality of choice, best visualizes disc herniation, nerve root compression, and soft tissue
- CT lumbar spine: alternative when MRI is contraindicated (e.g., certain implanted devices)
- Electromyography/nerve conduction studies: useful when the diagnosis is unclear or to differentiate radiculopathy from peripheral neuropathy or plexopathy
Laboratory tests (ESR, CRP, CBC) are reserved for suspected infection or malignancy, not routine uncomplicated sciatica.
Differential diagnosis
- Piriformis syndrome: sciatic nerve compressed by the piriformis muscle rather than at the spinal level; pain often worsens with hip internal rotation and sitting, normal imaging of the spine
- Lumbar spinal stenosis: typically older patients, bilateral symptoms, neurogenic claudication relieved by flexion (e.g., leaning on a shopping cart)
- Sacroiliac joint dysfunction: pain localized to the SI joint, provocative maneuvers (FABER test) reproduce pain without true dermatomal radiation
- Peripheral neuropathy: typically bilateral, stocking-glove distribution, associated with diabetes or other systemic causes
- Hip osteoarthritis: groin pain, pain with hip rotation, may mimic proximal radiation
- Vascular claudication: pain with exertion, relieved by rest (not position), diminished pulses, associated with peripheral arterial disease
- Spinal tumor or metastasis: night pain, weight loss, history of malignancy
- Cauda equina syndrome: bilateral symptoms, saddle anesthesia, bowel/bladder dysfunction, surgical emergency
Management
Most guidelines (including those from the American College of Physicians, NICE, and other major societies) emphasize conservative management as first-line therapy, since most cases resolve spontaneously within weeks.
Conservative management
- Patient education and reassurance about generally favorable natural history
- Encourage continued activity as tolerated; avoid prolonged bed rest
- NSAIDs as first-line pharmacologic therapy for pain relief
- Physical therapy with directional exercises and core strengthening once acute pain allows
Pharmacologic options
- NSAIDs (first-line)
- Muscle relaxants (short-term adjunct for muscle spasm)
- Neuropathic agents such as gabapentin or duloxetine may be considered for persistent radicular pain, though evidence is mixed
- Opioids are not recommended as first-line and should be limited to short-term use in severe refractory cases
- Oral corticosteroids are generally not recommended; evidence for benefit is weak
Interventional options
- Epidural corticosteroid injection: may provide short-term pain relief in select patients with confirmed radiculopathy; does not alter long-term outcomes or surgery rates
Surgical management
Indicated for:
- Cauda equina syndrome (emergency decompression)
- Progressive or severe motor deficit
- Persistent disabling pain despite 6-8 weeks of conservative therapy with imaging-confirmed nerve root compression
Common procedure: microdiscectomy, which provides faster short-term relief than conservative care, though long-term outcomes at 1-2 years are often comparable between surgical and conservative groups in randomized trials.
Guideline note: there is some variation internationally regarding the timing of imaging and the role of epidural injections, but consensus is strong that red-flag-negative sciatica should start with conservative management.
Complications and prognosis
- Most patients (around 80-90%) improve significantly within 6-12 weeks with conservative management alone
- Chronic radiculopathy or persistent pain occurs in a minority and may require further intervention
- Cauda equina syndrome, if missed or treatment delayed, can result in permanent bowel, bladder, or sexual dysfunction and lower extremity weakness, making prompt recognition critical
- Recurrence rates for disc herniation-related sciatica are notable, particularly in patients who return to high-risk occupational activities
- Foot drop from severe L5 radiculopathy may persist despite treatment if axonal injury has occurred
SCIATICA red flags - think 'SCATS': Saddle anesthesia, Cauda equina signs, Anal sphincter tone loss, Trauma history, Systemic signs (fever, weight loss, malignancy history) — any of these mean urgent imaging, not routine conservative care.
Practice questions
1. A 42-year-old man presents with 2 weeks of sharp pain radiating from his lower back down the posterior right thigh to below the knee. He reports difficulty dorsiflexing his right foot and numbness over the dorsum of the right foot. Straight-leg raise on the right reproduces the pain at 40 degrees. Which nerve root is most likely affected?
2. A 55-year-old woman with sciatica for 3 weeks has been managed conservatively with NSAIDs and physical therapy with minimal improvement. She has no red flag symptoms, normal strength, and no bowel or bladder changes. What is the most appropriate next step?
3. A 60-year-old man presents with acute severe low back pain, bilateral leg weakness, saddle numbness, and new urinary retention. Which is the most appropriate immediate step?
Frequently asked questions
What causes sciatica?
Sciatica is most often caused by a herniated lumbar disc compressing a nerve root, usually at the L4-L5 or L5-S1 level. Other causes include spinal stenosis, spondylolisthesis, and piriformis syndrome, where the sciatic nerve is compressed outside the spine. Less commonly, tumors, infection, or pregnancy-related changes contribute. The underlying mechanism combines mechanical pressure on the nerve root with local inflammation that sensitizes the nerve.
What are the first symptoms of sciatica?
The first symptoms are usually a sharp or burning pain starting in the lower back or buttock and radiating down one leg, often below the knee. This may be accompanied by tingling, numbness, or a feeling of weakness in the leg or foot. Pain commonly worsens with sitting, bending forward, coughing, or sneezing, and improves when lying down with knees bent.
How is sciatica diagnosed?
Sciatica is diagnosed mainly through history and physical examination, including the straight-leg raise test and checking for dermatomal sensory loss, muscle weakness, and reflex changes. Imaging such as MRI is reserved for cases with red flag symptoms, progressive weakness, or pain that fails to improve after 4-6 weeks of conservative treatment. Routine imaging in the first few weeks is not recommended because most cases resolve on their own.
Is sciatica curable?
Most cases of sciatica resolve on their own within 6-12 weeks with conservative treatment such as NSAIDs, activity modification, and physical therapy. A minority of patients develop chronic or recurrent symptoms, particularly if the underlying disc herniation is severe or activities that strain the back continue. Surgery can effectively relieve symptoms in persistent or severe cases, though it is not always necessary for long-term resolution.
Sciatica vs piriformis syndrome — what is the difference?
Sciatica from disc herniation originates at the spinal nerve root, typically with back pain, dermatomal sensory loss, and reflex changes, and is confirmed with spinal MRI. Piriformis syndrome compresses the sciatic nerve outside the spinal canal, in the buttock, so spinal imaging is normal; pain often worsens with hip internal rotation, prolonged sitting, or climbing stairs, without true nerve root signs like reflex loss.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: M54.3
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.