Clinical Features of Sciatica
Sciatica is characterized primarily by pain radiating down the leg below the knee in the distribution of the sciatic nerve, suggesting nerve root compromise due to mechanical pressure or inflammation. 1
Definition and Pathophysiology
- Sciatica is a symptom rather than a specific diagnosis, and is the most common manifestation of lumbar radiculopathy 1
- It is caused by a herniated lumbar disc in the vast majority of cases, with compression and inflammation of nerve roots 2
- Most symptomatic lumbar disc herniations (over 90%) occur at the L4/L5 and L5/S1 levels 3
Key Clinical Features
Pain Characteristics
- Pain radiating from the back into the leg, extending below the knee and potentially into the foot and toes 2
- Pain in the leg that is typically greater than accompanying low back pain 4
- Pain may have a neuropathic character with burning, electric sensation, or dysesthesia 3
- Pain may be aggravated by flexion and extension of the spine, walking, or running 3
Neurological Findings
- Sensory deficits in the affected dermatome (L4, L5, or S1 distribution) 3
- Motor weakness corresponding to the affected nerve root: 3
- L4 nerve root: knee strength deficits
- L5 nerve root: great toe and foot dorsiflexion weakness
- S1 nerve root: foot plantarflexion weakness
- Diminished or absent reflexes (particularly ankle reflex for S1 involvement) 3
Diagnostic Tests
- Straight-leg-raise test has high sensitivity (91%) but modest specificity (26%) for diagnosing herniated disc 3, 1
- Positive when leg pain is reproduced between 30-70 degrees of leg elevation 3
- Crossed straight-leg-raise test is more specific (88%) but less sensitive (29%) 3, 1
- Positive when raising the unaffected leg produces pain in the affected leg 5
Clinical Course and Associated Features
- The clinical course of acute sciatica is generally favorable, with most pain and related disability improving within 2-4 weeks with or without treatment 2
- Symptoms may be exacerbated by sitting, coughing, sneezing, or Valsalva maneuvers 6
- Pain may vary throughout the day and be influenced by body position and movement 1
- Psychosocial factors and emotional distress are stronger predictors of outcomes than physical examination findings or pain severity/duration 3
Differential Diagnosis Considerations
- Referred pain from the lower back (non-radicular pain) 6
- Piriformis syndrome (sciatic nerve compression by the piriformis muscle) 1
- Spinal stenosis (pseudoclaudication with pain relieved by sitting) 3
- Cauda equina syndrome (urinary retention has 90% sensitivity) - a medical emergency 3, 5
Red Flag Symptoms Requiring Urgent Evaluation
- Rapidly progressive or severe neurological deficits 3
- Bladder or bowel dysfunction, especially urinary retention 3
- Fecal incontinence 3
- Saddle anesthesia (loss of sensation in the perineal region) 7
Diagnostic Approach
- Clinical diagnosis is primarily based on history and physical examination 2
- Imaging (preferably MRI) is warranted if: 2
- Evidence suggests underlying pathology other than disc herniation
- Symptoms are severe and do not improve after 6-8 weeks of conservative treatment
- Red flag symptoms are present
Understanding these clinical features helps differentiate true sciatica from other causes of back and leg pain, allowing for appropriate management and treatment decisions.