Sciatica is defined as well-localized leg pain that corresponds to a dermatomal distribution of the sciatic nerve (L4-S3). It is a unilateral, sharp, shooting pain, radiating down the posterior lateral aspect of the leg to the foot or ankle. It’s often associated with paresthesia in the same distribution and sometimes motor weakness.

Differential diagnosis

The most common cause of sciatica is a herniated lumbar disc (HLD). Differential diagnosis includes degenerative spine disease (e.g. spinal stenosis or spondylolisthesis), acquired cysts (e.g. synovial), trauma (pelvic or hip fracture/dislocation), infectious causes such as discitis, and neoplastic lesions such as schwannoma or metastasis. Peripheral neuropathies can mimic sciatica (e.g. fermoral/peroneal or diabetic neuropathy) as can intermittent vascular claudication or non-dermatomal referred pain from a non-spinal origin.

Red flags

History and physical examination should focus on ruling out sinister causes of sciatica such as tumour, infection, fracture or cauda equina syndrome (CES). “Red flag” signs and symptoms include fever or chills, back pain not relieved by rest, and vertebral tenderness to palpation. It’s important to elicit any history of cancer, known urinary tract or other infection, intravenous drug use, immunosuppression (e.g. HIV, transplant or chronic steroid use), and a history of trauma, which may be minor in patients > 70 or with prolonged steroid use causing osteoporosis.

CES is caused by sudden compression of multiple lumbar/sacral nerve roots in the spinal canal causing bilateral sciatica, loss of anal sphincter tone, urinary retention or overflow incontinence, saddle anesthesia (anus, genitals, perineum and buttocks) and unilateral or bilateral progressive lower extremity weakness. CES is a surgical emergency and requires urgent referral to a centre with neurosurgery or orthopedic spine surgeons. Delay of treatment of CES can leave patients with permanent disability.

Imaging is indicated on an urgent or emergent basis in patients with red flags for serious pathology. Otherwise, imaging for HLD is only helpful for potential surgical candidates and not necessary in the first 4-5 weeks of symptoms. MRI is the gold standard for diagnosis. Electromyogram/nerve conduction studies are helpful to diagnose peripheral neuropathies that can mimic radiculopathy but only indicated when there’s clinical suspicion of neuropathy.

Treatment

Treatment for sciatica caused by HLD begins with conservative therapy. Patient education and reassurance is vital as 85-90% of patients will recover within 1-3 months without surgical management. Some patients require bed rest; however, this is indicated only for 2-4 days and can otherwise be harmful. Modification of daily activities and work tasks should be advised such that a tolerable level of discomfort is achieved. This may require restriction from heavy activity like lifting. Exercise such as walking, cycling or swimming is aimed at maintaining physical and cardiovascular health and you should encourage it. This may be part of a physiotherapy program. Simple analgesia such as acetaminophen or NSAIDs are often sufficient. For severe radiculopathy opioid analgesics or pregabalin and gabapentin can be used. Non-surgical treatments for low back pain include lumbar spine manipulation or traction, transcutaneous electrical nerve stimulation (TENS), heat therapy, acupuncture and focal injections of corticosteroids to trigger points, ligamentous structures, facet joints or epidurally. These are of uncertain efficacy and should not be used as long-term therapy.

Most surgeons consider surgical intervention appropriate only after conservative medical management for at least 3 months has failed. Expedited surgical intervention is considered for patients whose pain can’t be controlled, despite adequate analgesics, who are likely to ultimately require surgery. This is a matter of clinical discretion and opinion varies between surgeons.

Psychosocial factors can confound a patient’s reporting of pain severity and can perpetuate the duration of their pain. Psychosocial conditions are suggested by a history of depression or substance abuse, especially narcotics, discontent with current employment, pending litigation or workers compensation application, failure of previous treatments, inconsistent reproducibility (e.g. positive SLR without pain on sitting), and motor and sensory findings inconsistent with an anatomic distribution.

Back to Shirley

Returning to Shirley, her findings are consistent with a right S1 radiculopathy due to L5-S1 HLD. Advise her to continue conservative management. Reassure her with the expectation that her pain will improve within 3 months. Prescribe analgesia to provide adequate pain relief to allow normal activities of daily living and work duties. This may include opiates or medication targeted at neuropathic pain (e.g. gabapentin). MRI isn’t needed immediately but is required if severe pain persists beyond 4-5 weeks. If findings on MRI are consistent with surgical pathology that anatomically correlates to her right S1 radiculopathy then a surgical opinion is warranted. Tell her to seek urgent medical attention if she experiences any progression in her motor deficit, any of the red flags described above, or symptoms of CES.