Evaluation and Management of Acute Low Back Pain

Emerg Med 36(7):20-28, 2004

Common as it is, low back pain must always be carefully evaluated as a possible symptom of serious illness, the authors warn. They explain how to do it efficiently and effectively.

By David Della-Giustina, MD, FACEP, and Robert Nolan, DO, DC

Low back pain is a very common patient complaint that can be difficult to evaluate and manage. Afflicting up to 90% of the U.S. population at some point in their lives, it is second only to upper respiratory infection as a cause for symptom-related visits to primary care physicians.

The costs associated with management and treatment of low back pain are enormous. It is the most common cause of work-related disability in persons under age 45 and the second most common cause of temporary disability for all ages. It is estimated that well over $60 billion is spent annually in direct and indirect costs for diagnosing and treating low back pain.

Most studies indicate that acute low back pain is a self-limiting condition that usually resolves in six weeks. In up to 84% of low back pain sufferers, no clear cause is ever determined. There is a small subset of patients, however, in whom the acute pain signals a life-threatening disease or disorder that requires immediate intervention. For this reason, all patients experiencing acute low back pain should be evaluated carefully.

In this article, we will discuss the evaluation and management of acute low back pain, with a primary focus on the "red flags" that warrant a more detailed assessment. In addition, we will review special circumstances that require a particular treatment regimen.
 

HISTORY IS KEY

Low back pain is defined as pain located between the lower rib cage and the gluteal folds, often extending or radiating into the thighs. Acute low back pain is defined as pain lasting less than six weeks; pain lasting between 6 and 12 weeks is considered subacute; and pain lasting longer than 12 weeks is termed chronic.

The history is the key to identifying the patient's principal diagnosis. It needs to focus on identifying and eliminating red flags, historical factors that should raise the clinician's suspicion for a serious etiology (see quick reference list in the box below). The presence or absence of these red flags will guide the clinician to an appropriate and cost-effective evaluation.

Age. If the patient is more than 50 years old or younger than 18, that is a red flag because these age groups are at higher risk for a serious etiology. More specifically, patients older than 50 are at increased risk for tumor, abdominal aortic aneurysm, and infection; those older than 65 have an increased risk of hypertrophic degenerative spinal stenosis. Children under age 18 are at increased risk for congenital defect, tumor, infection, spondylolysis, and spondylolisthesis.

Duration of the pain. Approximately 80% of patients with acute low back pain will be symptom-free within six weeks. Pain lasting longer than six weeks is a red flag for tumor, infection, or a rheumatologic etiology and warrants further evaluation with diagnostic testing.

Location and radiation of the pain. Pain that is caused by muscular or ligamentous strain or disk disease without nerve involvement is located primarily in the back, often with radiation into the buttocks or thighs. Pain that radiates below the knee, especially into the calf and foot, is a red flag that raises concern for nerve root inflammation below the L3 level. This radiculopathy below the knee is important to identify because approximately 95% of all herniated disks occur at the level of either L4-L5 or L5-S1.

History of trauma. Any history of major trauma or even minor trauma in an elderly patient or chronic steroid user is a red flag for the possibility of fracture. Minor trauma in these patients is significant because they are more likely to have osteoporosis. Seemingly innocuous injuries such as a fall from a standing or a seated position may produce enough force to result in a fracture in some osteoporotic individuals. Plain x-rays of the involved regions should be taken.

Systemic complaints. Constitutional symptoms such as fever, night sweats, malaise, or unintended weight loss suggest infection or malignancy. These complaints are more worrisome for infection if the patient has additional risk factors, such as a recent bacterial infection or immunocompromised status, or if the patient is an injection drug user. Back pain in an injection drug user should be assumed to be osteomyelitis or epidural abscess until these conditions are ruled out by diagnostic studies. Further, recent invasive procedures, such as colonoscopy, may predispose the patient to infection secondary to bacteremia.

Atypical pain. Benign low back pain is usually described as a dull, achy pain that is exacerbated with movement and improves with rest. Red flags for tumor and infection include pain that is worse at night and often awakens the patient from sleep, is not relieved with rest, or is unrelenting despite appropriate analgesic treatment. Many patients will complain of being uncomfortable and having difficulty getting to sleep because of their symptoms. While bothersome, this is not a red flag. Rather, it is the severe pain that awakens the patient from sleep and is often worse than daytime symptoms that is of greater concern. Pain that is worsened with prolonged sitting, coughing, and the Valsalva maneuver often occurs with disk herniation.

Associated neurologic deficits. Patients with benign acute low back pain rarely have associated neurologic deficits. Any such deficit or complaint is a red flag. Epidural compression syndrome (spinal cord compression, cauda equina syndrome, or conus medullaris syndrome) commonly manifests with saddle anesthesia, bowel or bladder incontinence, erectile dysfunction, or a severe and progressive neurologic deficit. Residual bladder volumes can be measured to help assist in the evaluation of bladder incontinence. Large post-void residual volumes in the presence of low back pain suggest significant neurologic compromise and warrant immediate evaluation for epidural compression syndrome. A negative post-void residual volume is reassuring and effectively rules out significant bilateral neurologic compromise.

Other complaints of worsening paresthesias, weakness, and gait disturbances need to be evaluated to determine if these symptoms can be explained by a single nerve root pathology, most likely from compression by a herniated disk, or multiple or bilateral nerve root complaints, which raises concern for compression from a mass.

History of cancer. A history of cancer is a red flag because of the risk of metastatic spread to the spine. The cancers that are most likely to metastasize to the spine are breast, lung, thyroid, kidney, and prostate cancer. Primary tumors originating in the spine include osteosarcoma, lymphoma, multiple myeloma, and neurofibromas.

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FINDINGS ON PHYSICAL EXAMINATION

The physical examination of the patient with back pain need not be long or complex. The examination should be focused on the patient's vital signs, general appearance, and the back itself.

Obvious derangements in vital signs are always of concern. The presence of fever, as noted earlier, is a red flag for infection. Fever is present in 27% of patients with tuberculous osteomyelitis, 50% of patients with pyogenic osteomyelitis, and up to 87% of patients with spinal epidural abscess. However, it should be kept in mind that the absence of fever does not rule out spinal infection.

In terms of general appearance, most patients with benign low back pain prefer to remain still. Individuals writhing in pain or in extreme pain should raise concern for spinal infection, abdominal aortic aneurysm, or nephrolithiasis.

Evaluating the back does not require a detailed orthopedic examination. The clinician should concentrate on evaluating for signs of trauma, infection, or neurologic compromise. The back should be exposed and palpated. If there is a history of trauma, the focus should be on the midline spinous process to evaluate for tenderness. Muscular spasm or edema should also be noted.

Lower extremity strength and sensation should be evaluated, focusing on the muscle groups and dermatomes innervated by specific spinal nerve roots. Patellar and Achilles reflexes should be compared for symmetry, and Babinski's test should be performed to evaluate for an upper motor nerve syndrome. All deficits or abnormalities should be compared with the nerve root involved. For example, weak plantar flexion of the left foot in addition to a hyporeflexive Achilles reflex and diminished sensation in the lateral foot corresponds well with S1 nerve root compression.
 

STRAIGHT LEG RAISE TEST

The straight leg raise test is an easy test to perform to evaluate the patient for disk herniation. The patient is placed in the supine position and the leg is elevated by the clinician up to 70 degrees. A positive test reproduces radicular pain below the knee along the path of a nerve root in the 30- to 70-degree range of elevation. A positive test result can be further verified by lowering the leg 10 degrees from the point of radicular pain and dorsiflexing the foot. This should produce a similar radicular pain. Reproduction of the patient's back pain or pain in the hamstring is not a positive test.

A positive straight leg raise test is approximately 80% sensitive for disk herniation. Further, if there is radicular pain down the affected leg when the asymptomatic leg is raised (positive crossed straight leg raise), it is highly specific but not sensitive for disk herniation.

A rectal examination does not need to be performed on all patients suffering from low back pain. However, it is indicated for those patients with red flags, especially those with neurologic complaints or severe pain. On examination, evaluate the patient for perianal sensation, rectal tone, and rectal and prostatic masses. In those with abnormal tone or sensation, the bulbocavernous reflex can be tested and the anal wink evaluated. Poor rectal tone in association with back pain and saddle anesthesia indicates an epidural compression syndrome.

In 1980, Waddell described five physical signs that were associated with nonorganic back pain (see box below). He found that patients who had three or more of the five signs were more likely to have nonorganic disease.

DIAGNOSTIC TESTING

Beyond the history and physical examination, the question always arises as to which ancillary studies need to be included in the workup of acute low back pain. When there are no red flags, a good history and physical exam should suffice. When red flags are present, however, further evaluation with the following diagnostic tests is warranted.

Laboratory tests. If red flags for infection or tumor are present, a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and urinalysis may help narrow the differential diagnosis. The CBC is obtained primarily to evaluate for an elevated white blood cell (WBC) count that is consistent with infection. However, a normal WBC count does not rule out infection. An elevated ESR is almost always seen with infection and rheumatologic disease; it is also a marker of an undiscovered malignancy. The CRP level is used in the same fashion as the ESR, although the utility of CRP in diagnosing spinal infection or tumor has never been evaluated in the literature. Urinalysis is used to look for a urinary tract infection in patients who have evidence of spinal infection, because the urinary system is a common primary source for such infections.

Radiography. Plain radiographs rarely yield any helpful information in diagnosing patients with acute low back pain. However, they do increase the cost of the evaluation and the time it takes to conduct it, and they subject the patient to unnecessary radiation. In the absence of red flags, plain films are simply not necessary. If there is a concern for fracture, infection, rheumatologic disease, or metastatic disease, then anteroposterior and lateral films should be obtained. Oblique views are not necessary; they add little new information. If the anteroposterior and lateral films are negative but concern still exists about the above differential, then magnetic resonance imagery (MRI) or computed tomography (CT) may be warranted.

Magnetic resonance imagery. This test is the gold standard diagnostic imaging technique when a compressive lesion of the spinal cord or the cauda equina, spinal infection, or disk herniation is suspected. If disk herniation is the only concern, this examination may be delayed for four to six weeks.

Computed tomography. This is the study of choice for evaluating bony structure, which is most important in the setting of spinal trauma and the need to determine the stability of the spinal column and integrity of the spinal canal. In the absence of MRI, a CT-myelogram may be used to assess for epidural compressive lesions. Computed tomography is also a good imaging modality for detecting vertebral osteomyelitis. However, due to poor resolution of the spinal canal, it can miss an epidural abscess unless myelography contrast is used.

Bone scan. If metastatic spread of cancer is a concern but the patient has no neurologic symptoms, bone scan is an excellent choice. While inferior to an MRI, it will help identify infectious processes as well as stress fractures.
 

TREATMENT OF BENIGN ACUTE LOW BACK PAIN

About 80% of acute low back pain sufferers will recover full activity within one month of symptom onset. While no treatment is certainly an acceptable option, most patients want some form of therapy for their complaint. The goal of treatment in this population is to prevent immobility and provide acceptable analgesia while the condition resolves.

Activity. Prior to the 1980s it was common to prescribe seven days of bed rest for acute low back pain. This has been well studied, and the presumed benefit of bed rest has been convincingly refuted. Recent studies found that patients who resumed their normal activities to whatever extent they could tolerate recovered faster than those who stayed in bed for two days. On the other hand, active exercise has not been shown to be beneficial during the acute stage of back pain. Once the patient recovers, however, exercise may help prevent future episodes. Patients should be advised to resume normal daily activities and curtail activities that exacerbate the pain.

Analgesia. The mainstays of pharmacologic therapy are acetaminophen, nonsteroidal anti-inflammatory drugs (NSAIDs), and opiate analgesics. Acetaminophen is an excellent analgesic that has proven efficacy comparable to NSAIDs. It is also inexpensive and has a relatively innocuous side-effect profile. We recommend treatment with acetaminophen for all patients with back pain unless there is a specific contraindication, such as liver disease or allergy.

Most NSAIDs are equally efficacious in the management of acute pain. It is usually best to choose a particular NSAID based on its side-effect profile and cost. The lowest dose of medication needed to reduce the patient's pain should be tried. If there is a concern about gastrointestinal bleeding, misoprostol or a proton pump inhibitor should be added to the treatment regimen. The new COX-2 inhibitor NSAIDs are a reasonable but more expensive alternative for the patient with a history of gastrointestinal bleeding.

The approach we recommend is to use a combination of acetaminophen and NSAIDs. A popular dosing regimen is acetaminophen 650 to 975 mg orally every four to six hours, in combination with either ibuprofen 800 mg three times daily or naproxen 250 to 500 mg twice daily. Ketorolac has not been shown to be superior to oral NSAIDs in the management of acute musculoskeletal pain.

Opiate analgesics should be offered to those patients with moderate to severe pain. Back symptoms can get very painful, and our goal is always to minimize the patient's pain while allowing him or her to continue with routine activities. It is advisable not to prescribe more than one week's worth of medication. Combinations of acetaminophen and codeine phosphate, hydrocodone, or oxycodone may be used. To avoid acetaminophen toxicity, however, patients should be cautioned not to take acetaminophen in addition to these opiate-acetaminophen combinations.

Other medications commonly prescribed to treat acute low back pain include muscle relaxants, such as diazepam, methocarbamol, and cyclobenzaprine. While these medications are efficacious in relieving back symptoms, there does not appear to be a synergistic effect with NSAIDs or acetaminophen. Muscle relaxants are most beneficial in treating low back pain accompanied by muscle spasm. Some clinicians advocate the use of corticosteroids systemically or by local injection; however, this treatment has never been shown to be beneficial and we do not recommend it.

Manipulation. Perhaps the most controversial treatment for acute low back pain is manipulation. Many studies have looked at the efficacy of manipulation in this population, and most have found that while it may have some limited short-term benefit, the lasting benefit is unproven. Some studies have shown that manipulation is no better than physical therapy and only slightly better than an educational booklet with regard to patient satisfaction at one and four weeks. Neither manipulation nor physical therapy has been shown to be cost-effective, however, or to significantly reduce recovery time.

Other physical modalities. Other common treatments include traction, diathermy, cutaneous laser therapy, exercise, ultrasound, homeopathy, acupuncture, massage, and transcutaneous electrical nerve stimulation. None of these treatments, however, has been shown to improve the recovery rate from acute low back pain. Heat and ice therapy have the benefit of being very inexpensive and may be marginally effective in reducing pain.
 

LOW BACK PAIN WITH SCIATICA

Sciatica, or pain radiating along a nerve root path to the foot, afflicts 2% to 3% of patients with low back pain. The pain is usually due to compression of a nerve root by a herniated nucleus pulposus in the intervertebral disk. The majority of patients with a herniated disk will complain of low back pain, but most of their pain will be located in the leg, with associated weakness, paresthesias, and numbness along a nerve root. More than 95% of disk herniations occur at the L4-L5 or L5-S1 levels, corresponding to L5 or S1 radiculopathies.

Other causes of nerve root irritation must be considered, such as space-occupying lesions (including central canal or foraminal stenosis, usually found in patients over age 50), tumor, hematoma, and infection. Red flags from the history and physical examination will help differentiate this diagnosis. The outcome for patients with a herniated disk is generally positive, with 50% recovering in six weeks and only 5% to 10% ultimately requiring surgery. Interestingly, two good studies demonstrated that the results from surgery appear to be better only for the first two postoperative years after the procedure. The studies found no difference in patients' symptoms 4 and 10 years after surgery.

Management of back pain patients with sciatica is similar to that for patients with uncomplicated acute low back pain—limited bed rest, activity as tolerated, and analgesics. One difference is in the use of steroids. While there is no role for systemic steroids, epidural steroid injection has been shown to produce a mild to moderate reduction in pain, but with no proven reduction in the need for surgery.

Generally, plain film radiographs are not required in this patient population. If they are obtained, it should be to rule out bony pathology, such as tumor, infection, or fracture; they will not rule in disk herniation. While MRI is the best imaging modality for detecting disk herniation, it need not be obtained emergently unless the patient has a progressing neurologic deficit, because symptoms will resolve or significantly improve in 50% of these patients by week 6. For those patients whose symptoms do not resolve or improve by that time, an MRI would be appropriate. Consultation with a specialist is necessary in these cases and with patients who have progressing neurologic deficits.

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EPIDURAL COMPRESSION SYNDROME

A collective term, epidural compression syndrome encompasses spinal cord compression, cauda equina syndrome, and conus medullaris syndrome. The term is used to group these syndromes together for two reasons. First, except for the level of the neurologic deficit, the presentation of these syndromes is similar. Secondly, until the actual diagnosis is known, initial evaluation and management of these syndromes are similar.

Epidural compression syndrome is a medical emergency because of the catastrophic neurologic loss that can develop if it is not recognized and treated promptly. While the diagnosis of complete epidural compression is obvious, evaluating patients with early signs and symptoms is more difficult. The initial differential diagnosis is broad and includes most conditions that cause weakness, sensory changes, or autonomic dysfunction. One of the keys to the diagnosis is determining whether the symptoms are bilateral and evaluating the combination of motor, sensory, and autonomic dysfunction.

Interestingly, these patients usually have minimal low back complaints. Leg pain may be a more frequent complaint. In addition, patients may experience constipation or incontinence of the bowel, as well as urinary retention or incontinence. Post-void residuals or urinary retention with overflow incontinence is indicative of a denervated bladder, commonly seen in this condition. Patients often complain of saddle anesthesia and have a decreased rectal tone. Major motor and sensory loss is frequently noted.

These conditions all arise from pressure being exerted on the central cord or cauda equina from a space-occupying lesion. Possible etiologies include a large central disk herniation, spinal canal hematoma, spinal canal abscess, primary or metastatic tumor, or traumatic compression. These patients are to be treated emergently, and it should be assumed they have a spinal cord injury. Treatment is dexamethasone 10 to 100 mg intravenously, which should be administered as soon as the condition is suspected rather than waiting for the results of diagnostic tests that may take several hours to obtain.

While the recommended dose of 100 mg is much more than usually prescribed, high-dose systemic corticosteroids may reduce the progression of deficits in epidural compression syndromes and alleviate pain in cases of compression due to malignancy. Appropriate imaging includes an emergent MRI of the cervical, thoracic, and lumbosacral spine if there is concern about possible metastatic compression or infection; otherwise, a regional MRI of the area affected will suffice. A plain film x-ray of the area may also be obtained. Immediate consultation with a specialist is required.

Outcomes with these patients largely depend on their neurologic deficits at the time of presentation. In studies evaluating patients with epidural compression due to tumor, those who were paraplegic on presentation were unlikely to walk again. Those who were too weak to walk without assistance, but not paraplegic, had a 50% chance of walking again. Those who were ambulatory at the time of presentation usually remained so. Of those who had to be catheterized for a denervated bladder, 81% did not recover bladder function. Thus, recognition of those patients who present with mild symptoms is paramount, so that they have the greatest chance of retaining neurologic function with appropriate treatment.
 

VERTEBRAL OSTEOMYELITIS: OFTEN MISSED

Vertebral osteomyelitis is often missed on routine examination, with up to 50% of patients having symptoms for more than three months prior to being diagnosed. The history can be very helpful in making the diagnosis. About 90% of patients with this condition will have back pain as their primary symptom. This pain, which is often severe, is commonly nocturnal and unremitting despite appropriate rest and analgesics. Only 52% of patients will be febrile at the time of presentation, and only 10% will appear septic or toxic. Consequently, the absence of fever does not rule out this diagnosis. A history of injection drug use and back pain should be assumed to be osteomyelitis or epidural abscess until proven otherwise. Other historical clues are a recent urinary tract infection, pneumonia, or gastrointestinal or genitourinary procedure.

Transplant patients and other immunocompromised patients such as diabetics are at increased risk for septicemia and osteomyelitis. Staphylococcus aureus is the most common causative organism, but Escherichia coli, Proteus, and Pseudomonas are also known pathogens. Most of these infections are hematogenously spread and deposit in the vertebral matrix around the sluggish venous plexuses.

Evaluation of patients suspected of having vertebral osteomyelitis includes laboratory testing and radiographic exams. The WBC count may be elevated, but a normal WBC cannot be used to rule out infection. The ESR is almost always elevated (95% to 98% of the time) in the immunocompetent patient, as well as in the majority (90%) of immunocompromised patients. Urinalysis is helpful if the urinary tract is suspected as a primary source of infection. Interestingly, blood cultures are positive in more than 40% of these patients and should be drawn in those who are suspected of having this condition, preferably before any antibiotics are given.

Plain radiographs of the involved area should be obtained, but they may be normal because changes on x-ray usually lag behind clinical findings by two to three weeks. Radiographic evidence of infection includes bony destruction, moth-eaten end plates, and narrowing of disk spaces. The gold-standard imaging modality for diagnosing osteomyelitis and epidural abscess is MRI. Findings include brightening of the marrow on T2, brightening of the disk on T2, and darkening of the marrow on T1.

The cornerstone of treatment for osteomyelitis is IV antibiotics. Usually six to eight weeks of IV antistaphylococcal antibiotics are required. The antibiotic regimen may be tailored to blood culture results as well as the clinical response. It is important to try to identify the infecting organism, so that the proper antibiotics are utilized. The IV regimen is followed by oral antibiotics for another four to eight weeks. Further treatment includes analgesics, bed rest until symptoms improve, and immobilization with an orthosis. Surgery is reserved for those patients who have significant abscesses, spinal cord compression, and significant bony destruction or are unresponsive to standard medical treatment.
 

BACK PAIN IN THE CANCER PATIENT

Evaluating the cancer patient with back pain is more difficult because of the risk of spinal metastases and the potential devastating consequences if a significant lesion is missed. The best way to approach these patients is to separate them into three groups based on their symptoms.

The first group is patients with signs and symptoms of progressive epidural compression. As previously noted, this is a true medical emergency. These patients should be managed with high-dose steroids and emergent MRI as discussed under management of epidural compression.

In the second group are patients who have mild, stable symptoms that have been present for several days to weeks. In addition to having back pain, patients in this group have isolated nerve root involvement. (Involvement of more than one nerve root or bilateral neurologic involvement would place them in the first group.) These patients do not require high-dose steroids or emergent MRI. However, an MRI evaluation should be done within 24 to 48 hours and the patient should receive 4 to 10 mg of IV or oral dexamethasone while awaiting the results. Plain radiographs may assist in the diagnosis of metastases, but normal films do not rule out early metastases or tumors that do not involve the bone.

The majority of cancer patients suffering from back pain will fall into the third group. These patients have isolated pain with no neurologic deficits or complaints. Plain radiographs of the area involved should be obtained. If metastases are detected, an MRI should be performed to better define the degree of involvement. If no bony pathology is noted, the patients should be followed closely for two to three weeks. If they continue to have symptoms after that period of time, they should be imaged further with an MRI or CT scan. It is important to remember that 50% bony destruction must occur before radiographs can detect a lytic lesion, and 60% of patients with metastatic disease will have normal radiographs.
 

RECURRENT OR CHRONIC BACK PAIN

Evaluation and management of patients with chronic back pain is similar to the acute patient. The focus should be ensuring that an appropriate workup has been conducted. Are there red flags other than pain duration? Has the patient ever been pain-free or has the pain been truly chronic?

If the patient is experiencing an acute exacerbation of a chronic problem, it can be treated like uncomplicated low back pain. If it is a continuation of acute pain, then radiographic and laboratory evaluations should be performed, if they have not already been done. Specifically, a two-view radiographic series, CBC, ESR, and urinalysis should be obtained. The history should be evaluated again for missed red flags, and the physical examination should ensure that there are no new findings. If there are new red flags, then the patient should be approached like any other patient with acute back pain. If an MRI or CT has been performed in the past, the results should be reviewed for possible disk herniation, nerve root compression, or another abnormality that was overlooked.

If the workup is negative, the patient should be treated conservatively with NSAIDS and acetaminophen. Avoid opiate analgesics in these situations because the risk of addiction increases with chronic use. When patients with recurrent or exacerbated chronic low back pain present to an emergency department, their discharge instructions should include referral to their primary care physician or a pain specialist for chronic pain management.

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