NeuroNews
(Return to Newsletter Index)
Low Back Pain: A Brief Review
By Shihab U. Ahmed, M.D., M.P.H.
Division of Pain Medicine
Low back pain (LBP) is estimated to afflict 70 to 90% of people. It is the most common cause of disability in individuals under the age of forty-five. Although most acute attacks of LBP resolve within approximately 6 weeks, the reported recurrence rate can be as high as 75%. Contrary to popular belief, the diagnosis of LBP can often be established with precision-guided diagnostic tests, and pain relief can be achieved with targeted injection therapy.
Differentiating axial LBP from radicular pain is key to guiding therapy. Radicular pain indicates irritation of the nerve root from mechanical or chemical stimuli. In contrast, axial LBP (mechanical LBP) suggests pain associated with disc degeneration, facet or sacroiliac joint arthropathy, or other myofascial components of the spine.
Evaluation of patients with LBP
The initial evaluation of any patient with LBP should include a search for a potentially progressive or unstable underlying cause (see Red Flags). Patients with suspected trauma and or unstable neurologic deficits should be managed urgently, either in collaboration with or by immediate referral to a spine surgeon.
The pain history, documenting events surrounding the onset of pain, ought to be a part of a detailed medical history. For example, if a motor vehicle accident is the cause of pain, a thorough history including the use of a seat belt, single or multiple car involvement, and the mechanism of impact (e.g., collision from the rear or side of the vehicle) may be useful in formulating a differential diagnosis. The pain history should also focus on eliciting the location of pain, along with its duration, radiation, character (e.g., deep, superficial, sharp, aching, burning, shooting, pins and needles, etc.), and any exacerbating or alleviating factors. In all cases, it is important to include a psychosocial and family history to assess the degree of support available to the patient for coping with the chronic pain condition (see Yellow Flags).
|
Red Flags
|
Yellow Flags
|
|
History of major trauma
|
A negative attitude that back pain is harmful
|
|
History of cancer
|
Fear avoidance behavior
|
|
Unexpected weight loss
|
Reduced activity levels
|
|
Fever, immunosupression, IVDA
|
A tendency to depression, low morale
|
|
Disturbed gait, saddle anesthesia
|
A tendency to social withdrawal
|
|
Bladder or bowel incontinence
|
Social or financial problems
|
|
Severe or progressive neurologic deficit
|
A negative attitude to active treatment
|
Physical examination
A focused examination targeting the lower back should be included within a comprehensive general physical examination. Examination of the spine begins with noting the patient’s gait, posture, and any obvious deformity.
Closer examination of the entire length of the spine for scars, rash, or swelling follows. Palpation will detect any sensitivity of the skin (e.g., allodynia, which is suggestive of neuropathic pain). Firm palpation may be used to detect midline tenderness or a mass, paraspinal tenderness, or muscle tightness. A thorough neurological examination, including an assessment of sensation and strength and deep tendon reflexes is useful in ruling out associated spinal cord, nerve root, and peripheral nerve pathology. The range of motion of the spine must also be determined (i.e., flexion, extension, and lateral bending).
Diagnostic testing
Plain films may be useful in identifying fractures or ligamentous instability. It is important to include flexion and extension films whenever instability is suspected. Computed tomography (CT) is best for detecting bony abnormalities. Magnetic resonance imaging (MRI) is the imaging modality of choice under most circumstances and can differentiate small differences in soft tissue composition. MRI is considered the best technique for imaging infection, tumor, or suspected disc herniation. Electromyography (EMG) and nerve conduction velocity (NCV) testing are helpful in differentiating acute from chronic radiculopathy.
Common sources of LBP
Intervertebral discThe prevalence of disc-related pain among patients with chronic LBP is at least 39%. Discogenic pain often presents as deep, achy, axial pain. This type of pain can be referred to the buttocks and posterior thigh, but it does not extend to the distal extremities. Symptom onset is usually gradual, and pain is experienced with prolonged sitting (sitting intolerance), standing, and forward bending. Physical examination results are usually nonspecific, with limited range of motion at the affected segment or with pain on movement (particularly back flexion).
MRI and CT typically reveal only nonspecific findings. Provocative discography is useful in identifying the painful disc(s). This technique involves the injection of a small amount of radiocontrast dye into the suspected and adjacent discs in an attempt to reproduce the patient’s characteristic pain (concordant pain). Treatment for discogenic pain begins with conservative therapy, including physical therapy and oral NSAIDs. In patients with refractory discogenic pain demonstrated with provocative discography, treatment options may include intradiscal electrothermal therapy (IDET) or surgical fusion. Results from surgical fusion for a primary pain indication may be variable and should be pursued judiciously.
Facet joint
Facet joints are well innervated, and the estimated prevalence of LBP from facet joint etiology among injured workers is 15%. Pain originating from the facet joints has a similar presentation and may be difficult to distinguish from discogenic pain. Extension and lateral bending of the spine are usually painful. Pain is caused by stress on the facet joint capsule, secondary to loss of disc or vertebral height and normally accompanies degenerative disc disease. On physical examination, many patients may report paraspinal tenderness. Imaging studies may further demonstrate accompanying pathology, such as loss of disc or vertebral height, spondylolisthesis, or other degenerative changes. Diagnostic local anesthetic blocks under fluoroscopic guidance are the most accurate way to isolate the facet joint as the source of LBP. In patients with demonstrated facet joint pain, radiofrequency lesioning (RFL) [denervation] of the medial branch of the primary dorsal ramus can provide long-term pain relief.
Sacroiliac joint
The sacroiliac (SI) joint is a synovial joint with innervations from the dorsal rami of the L4, L5 and S1, S2 nerve roots. The prevalence of SI joint pain among chronic LBP sufferers is estimated to be 15%. Sacroiliac joint dysfunction typically presents with localized pain in the lower back or upper buttock overlying the SI joint. Pain may be referred to the posterior thigh, but pain extending below the knee is unusual. In most cases, an inciting event is not obvious and the onset is gradual over months to years. Physical examination may reveal localized tenderness over the joint. Degenerative changes of the joint on radiography are common and nonspecific. Resolution of pain following an intra-articular injection of local anesthetic under fluoroscopic guidance is the best diagnostic tool for SI joint pain. Currently, periodic intra-articular injection of a steroid with local anesthetic is the most common therapy for this type of pain.
Muscles
The back muscles are supplied by the posterior rami of the spinal nerves. In normal volunteers, injecting hypertonic saline to these muscles produces LBP and referred pain in the buttocks. Although the exact mechanism is not yet well understood, LBP with muscular etiology has been attributed to spasm, sprain and strain, or trigger points (as in myofascial pain).
A short course of muscle relaxants with NSAIDs may be adequate in many cases. Physical therapy (PT) is often an effective adjunct. Some refractory cases may benefit from a coordinated trigger point injection (TPI) followed by PT. Some practitioners recommend injection of botulinum toxin at the trigger point, following several positive responses from TPI using local anesthetics.
Spinal stenosis
Spinal stenosis includes both central canal narrowing and foraminal narrowing. Spinal stenosis is more common in older individuals and may be associated with age-related changes of the spine. MRI may be useful in delineating the extent and the causes of the narrowing. The clinical presentation of spinal stenosis includes LBP and lower extremity pain. Pain commonly worsens with walking (neurogenic claudication) and is temporarily improved with rest and forward bending. In mild to moderate cases of spinal stenosis, periodic epidural steroid injections may temporarily reduce symptoms of neurogenic claudication. If there is no improvement following epidural steroid injections, a surgical consultation may be sought to assess the possibility of benefiting from decompression surgery.
Failed back surgery syndrome
The diagnosis of failed back surgery syndrome (FBSS) is given to patients who suffer from chronic pain after spine surgery. It is important to note that the indications for surgery may vary. For example, it may have solely been performed for the purpose of pain relief. Other reasons include stabilization or decompression to treat a neurologic deficit. The pain may vary significantly, as well, and may have associated persistent neurologic deficits. Axial LBP in patients with FBSS may be related to pseudoarthrosis, facet arthropathy, or myofascial disease. In contrast, radicular pain may be related to nerve root irritation from epidural scarring. For patients with radicular pain, epidural steroid injection via the transforaminal or caudal route may prove to be useful. Spinal cord stimulation (SCS) has been shown to be an effective therapeutic modality for radicular pain from FBSS. In the treatment of axial pain, diagnostic local anesthetic facet blocks, followed (if appropriate) by radiofrequency facet denervation, can be beneficial. Unfortunately, SCS has proven less efficacious in treating axial LBP.
Summary
The physical examination has a limited role in the diagnosis of LBP; however, it is significant in ruling out serious pathology. It is essential to distinguish axial (mechanical) LBP from radicular pain of the lower extremity. Discogenic pain is the single most common cause for axial LBP. Clinical studies have shown that among patients suffering from chronic LBP, 40% have discogenic pain, 15% have SI joint pain, and 15% have facet joint pain. This obviously contradicts the popular belief that an anatomic diagnosis of LBP cannot be made in most cases. When LBP lasts for more than twelve weeks, an attempt should be made to establish an anatomic diagnosis. In many cases, LBP etiology can be established with fluoroscopy guided, controlled diagnostic injections under local anesthesia. Treatment may involve a multipronged approach, including therapeutic spinal injections, adjuvant medications, as well as physical and behavioral therapies.
|
