<< Back Pain: Cost-Effective Strategies For Distinguishing Between Benign And Life-Threatening Causes
ED Evaluation: Using The “Red Flags” Approach
While a search for red flags and directed testing is the most efficient known approach to the complaint of acute low back pain, it has its limitations. One major review found that the diagnostic accuracy of individual items of history taking, physical examination, and erythrocyte sedimentation rate are poor for predicting radiculopathy, vertebral neoplasms, and ankylosing spondylitis.5 However, the review noted that the combined history and the erythrocyte sedimentation rate had relatively high diagnostic accuracy in vertebral cancer. Getting out of bed at night and reduced lateral mobility were moderately accurate in detecting ankylosing spondylitis.
Other studies confirm the fact that a combination of historical factors suggests serious disease. In one study, the highest combination of sensitivity (.87) and specificity (.50) for a serious etiology of back disease occurred with any combination of: unable to sleep, awakened and unable to fall back to sleep, medication required to sleep, and pain worsened by walking.6
The Red Flags In The History
Is the patient younger than 18 years or older than 50 years? In both the old and the young, cancer is a more common etiology for back pain. In children, lumbosacral strain is rare, with the most common cause of back pain in adolescent athletes being spondylolysis or spondylolisthesis.7 Spondylolysis is a defect between superior articular process and the lamina of the vertebral body. When this is bilateral, the involved vertebra may slip forward (spondylolisthesis).
In the older patient, the emergency physician should always consider AAA as the etiology for the symptoms. In one series, back pain alone or in combination with abdominal pain was present in 53% of those with ruptured AAA and in 63% of patients requiring surgery for AAA.8
Duration And Acuity
Sudden-onset pain is compatible with AAA and renal colic. While mechanical low back pain may also be acute, most patients with lumbago complain of progressive symptoms. The majority of patients with lumbosacral sprain (LSS) will resolve or have significant improvement in their symptoms within six weeks.9,10 Pain that lasts greater than six weeks suggests infection or malignancy.11-13 Moreover, those with symptoms of more than six weeks duration are less likely to respond to usual conservative management.
Character Of Pain
Discomfort due to LSS is usually well-localized to the back and upper buttocks. Pain that radiates into the leg or foot indicates lumbar or sacral nerve root compression and may require further diagnostic studies, usually on an outpatient basis. Pain radiating to the groin can occur with both renal colic and AAA. It is classically taught that the pain of malignancy or infection does not improve with lying flat and resting, or is worse at night. Likewise, unrelenting pain despite adequate treatment and analgesics raises concern for serious disease.
Location Of Pain
While no well-designed studies address this issue, case series and textbook lore suggest the location of the pain will narrow the differential diagnosis. Pain confined to the mid and upper back may be related to chest pathology, such as thoracic dissection, myocardial ischemia, and pulmonary embolism. Abdominal disorders such as cholecystitis, pancreatitis, and peptic ulcer disease are thought to radiate more to the midback. Pelvic pathology produces pain in either the lower abdomen, lower back, or both.
Constitutional symptoms such as fever, chills, night sweats, and unexplained weight loss suggest either malignancy and infection.11,12,14 Associated symptoms outside of the musculoskeletal system are also important to elicit. Specifically, urinary, pulmonary, or gastrointestinal complaints point to diagnoses such as pyelonephritis, pneumonia, pancreatitis, or cholelithiasis. Most importantly, inquire about neurologic complaints. Target questions toward any new incontinence (bowel or bladder), erectile dysfunction, lowerextremity weakness or numbness, and saddle anesthesia. Patients with compression of the distal portion of the spinal cord (the conus medullaris) or the nerve roots in the spinal canal (cauda equina) may complain of acute urinary retention. A neurologic complaint should inspire a scrupulous neurologic examination in the ED to determine the presence of cord compression or cauda equina syndrome.
Past Medical History
A history of major trauma (and even minor trauma in the elderly) can be associated with vertebral fracture. Even strenuous lifting can cause fracture in the osteoporotic elderly. A history of cancer is a red flag for potential pathologic fracture from vertebral metastases or tumor involvement of the spinal canal or cord.
Moreover, a history of injection drug use or of an immunocompromised state such as diabetes, organ transplant, or HIV places the patient at an increased risk for vertebral osteomyelitis or epidural abscess.12,14
The Red Flags In The Physical Exam
In a similar manner, the physical examination has its own red flags. The general appearance of the patient is helpful. Patients with LSS generally lie flat and still, as moving, sitting, or standing worsens their pain. In contrast, the writhing patient may have a spinal infection or renal colic.13,15
Fever in the patient with back pain is concerning and signals potential infection. However, it is variably sensitive, ranging from 16% to 83%. The presence of fever depends upon the location of infection and the specific pathogen involved.12,14,16,17 Hypotension in the elderly patient with back pain may presage aortic rupture.
An abdominal exam is especially important when evaluating low back pain in the elderly. Specifically, one palpates for a pulsatile mass, auscultates for bruits, and evaluates femoral pulses. This said, physical examination alone is insensitive for AAA.18 Nearly half of all patients with AAA do not have a palpable mass,19 and one study suggests that neither bruits nor absent femoral pulses have any predictive value.20
The back exam begins with inspection. Specifically, look for erythema, contusions, and previous surgical scars. Examine the alignment of the back and determine the range of motion. Patients with ankylosing spondylitis may have loss of the normal lumbar lordosis and marked limitation in motion of the lumbar spine. Remember, however, that most forward flexion takes place at the hips and not necessarily in the lumbar spine. Next, palpate the back with specific attention to point tenderness. Then, percuss each vertebral body and note specific locations of tenderness. Percussion tenderness of the vertebral bodies is common with fractures and infection.15,17,21,22 This localization of pain guides the interpretation of radiographs.
An adequate neurologic exam is crucial, as it allows the emergency physician to identify potentially catastrophic disease. The exam begins with a sensory exam, which can adequately be accomplished with light touch and pinprick. If any deficit is noted, formal testing involving position sense, sharp/dull, as well as vibratory sensation may be helpful. An understanding of the sensory dermatomes (or a copy of the "AHCPR Tests For Low Back Pain") provides an important anatomic reference for sensory loss. A standard hospital pager set on "buzz" mode is a convenient "high-tech" substitute for a tuning fork (if you don't mind rubbing your beeper on someone's feet). "Saddle anesthesia" refers to a common finding in cauda equina syndrome that presents as decreased sensation over the buttocks, perineum, and proximal medial thighs.
The muscle groups of the lower extremities are individually tested against adequate resistance. Having the patient walk on their toes and heels is an excellent way to determine strength of the involved muscles. Testing of the patellar (L2-L4 nerve roots) and Achilles' (S1 nerve root) reflexes should follow. Impingement of the L5 nerve root does not produce a reflex abnormality (as there's no readily testable reflex for L5). However, there will be a sensory deficit in the L5 dermatome as well as weakness of the extensor hallucis longus (great toe dorsiflexion).
Babinski's sign is an abnormal reflex that appears when upper motor neuron innervation through the corticospinal tract is lost, as may occur with spinal cord compression. A positive Babinski's sign involves extension of the great toe and abduction (spreading apart) of the other toes with plantar stimulation, rather than the normal flexion response.23
The straight leg raise (SLR) test is helpful in identifying patients with nerve root compression by a herniated intervertebral disc, also termed a herniated nucleus pulposis (HNP). To perform this test, lie the patient supine then passively raise the straight leg anteriorly from 0 to 70 degrees. A positive test produces radicular pain below the level of the knee, in a dermatomal distribution. Isolated back pain triggered by this maneuver does not constitute a positive test. Radicular pain or sciatica worsens with foot dorsiflexion (Lasegue's sign) and abates by decreasing the leg elevation. A positive test result is approximately 80% sensitive for herniated disc.2,24
Radicular pain down the symptomatic leg when elevating the asymptomatic leg is a positive crossed straight leg test. This finding is highly specific, though insensitive, for herniated disc.2,24 An important point regarding the straight leg raise test is that it can be easily and stealthily performed while the patient is seated, using a similar leg extension and foot dorsiflexion.
Many conditions other than nerve irritation can cause a positive straight leg raise test, including myogenic pain, ischial bursitis, annular tear, and hamstring tightness. One test that may distinguish true sciatica is the sciatic stretch test. This maneuver can remove hamstring irritation as the cause of symptoms. In this test, the examiner raises the lower extremity with the knee extended until the patient experiences the leg symptoms. The physician then lowers the leg several degrees below the point of pain and applies popliteal compression. Compression of the popliteal fossa will tether the sciatic nerve. When the leg is elevated a second time, the patient with sciatica should experience symptoms with fewer degrees of elevation.25
The rectal examination will evaluate for rectal tone and sensation, prostatic and rectal masses, and to rule outperi-rectal abscess as the etiology for the pain.26 A rectal exam is not mandatory for every patient who complains of back pain (although its routine use may decrease ED visits for bcak pain). However, it should be performed in all patients with neurologic complaints or deficits. Poor or absent rectal tone in the presence of saddle anesthesia indicates an epidural compression syndrome, most commonly a cauda equina syndrome.
Numerous reports and clinical experience show that pelvic pathology can produce low back pain. However, the evidence-based literature is mute on the indications for pelvic examination in women with low back pain.
Tests For Non-Organic Pain
In 1980, Waddell wrote an important paper describing five physical signs associated with non-organic back pain. He proposed that most patients with proven organic back pain had only one or none of these criteria, while patients with three or more signs were likely to have non-organic disease.27 These signs have been wryly termed "yellow flags."
Since that time, Waddell's criteria have been used (some say abused) by physicians in the evaluation of low back pain. (See Table 2.) Cynics claim that patients who meet Waddell's criteria are malingerers searching for drugs or disability checks. Others believe that patients who display these findings do so unconsciously in an attempt to communicate their pain. One author suggested the following caveats when using Waddell's criteria:
- Because an increase in signs is associated with age, they are not recommended for use in the elderly.
- Behavioral signs can occur with organic findings. The presence of these signs does not contradict organic findings.
- Isolated behavioral signs are not clinically significant. A cut-off of three or more suggests nonorganic pain.28
Two additional tests are often employed to determine non-organic disease—the Hoover and the reverse sciatic tension test.25
To perform the Hoover test, the examiner places his or her hand under the heel of one foot and asks the patient to raise the opposite leg. If the patient genuinely tries to raise the leg the examiner will feel pressure applied to their hand. In a patient who is not sincere in their effort, there will be no contralateral pressure to the examining hand.
The reverse sciatic tension test may be useful in the patient with a positive SLR test. This maneuver is performed by plantar flexing rather than dorsiflexing the foot during the straight leg raise; if this results in increased complaints of pain, the patient is not organic.