The following lists the ‗red flags‘ to elicit in the history and physical examination for serious spinal causes of back pain, with their corresponding diagnostic considerations.
Constitutional symptoms including fever (cancer, epidural abscess, osteomyelitis)
IV drug use (epidural abscess, osteomyelitis) Immunocompromised status including
corticosteroid use (epidural abscess, osteomyelitis)
Pain worse at night (cancer)
Urinary retention or incontinence; or fecal incontinence (cauda equina)
History of cancer (spinal metastasis) Spinous process tenderness (spinal causes as
above)
‗Saddle‘ parasthesia or anesthesia (cauda equina syndrome)
Bilateral neurologic deficit or complaint (cauda equina syndrome)
Neurologic deficit at multiple nerve root levels Anticoagulant use or bleeding disorder (epidural
All contents copyright © 2012, University of Toronto. All rights reserved. Recent invasive spinal procedure including
epidural anaesthesia (epidural hematoma) The history should elicit the location, radiation and nature of the pain as well as palliative and
provocative factors. Typically, the description of back pain that has a benign cause is mild to moderate, dull, aching pain that is worse with movement, but improves with rest and lying still. Cough or Valsalva‘s maneuver that worsens the pain, usually signifies a musculoskeletal origin and may indicate a herniated disc in particular. Pain that is worse with flexion is consistent with lumbosacral strain and disc herniation. Pain that is worse at night, or is severe despite analgesics and lying still, often signifies a more serious cause. Associated neurologic symptoms such as sensory or motor deficits, gait disturbances and fecal or urinary incontinence should be sought after.
Risk factors for infection, cancer and vascular causes must be elicited to help heighten the suspicion for serious causes of back pain. Since the classic triad of spinal epidural abscess of fever, back pain and neurological deficits occurs in only 13% of confirmed cases, a history of IV drug use, chronic corticosteroid use and immunocompromised states must be asked about. Any patient with a known history of malignancy with new onset of back pain, should be considered to have spinal metastases until proven otherwise. Although prostate, lung and breast cancer are the most common culprits, any cancer can metastasize to the spine.
The physical examination is directed toward discovering ‗red flags‘. Examination of vital signs is of utmost importance with particular attention to fever. Inspect the skin for signs of infection and trauma. The abdomen should be palpated for aortic aneurysm, and the vertebral column as well as paraspinal muscles palpated for point tenderness. Perform a straight-leg test for sciatica. A positive straight-leg raise produces a pain that radiates below the knee into one or both legs. This radicular pain is improved by decreasing the elevation and worsened by ankle dorsifexion. Radicular pain below the knee in the affected leg when lifting the asymptomatic leg constitutes a positive crossed straight-leg raise, which is highly specific for nerve root compression by a herniated disc.
The neurologic examination must be thorough and directed toward each of the spinal nerve roots. Sensation, power and reflexes in the lower
extremeties must be elicited. In particular, sensation in the ‗saddle‘ area surrounding the anus and perineal area should be tested as well as rectal tone which may
both be decreased or absent in the setting of cauda equina syndrome. In addition, the anal wink reflex is elcited by gently stroking the skin lateral to the anus, which should cause a reflex of the external anal sphincter. The absence of sphincter contraction may indicate multiple sacral nerve root dysfunction.
INVESTIGATIONS
For patients with the presumed diagnosis of
lumbosacral strain or herniated disc in the absence of ‗red flags‘, no investigations are required since the vast majority of these patients will be asymptomatic within a few weeks. An emergency department bedside ultrasound can rule out an abdominal aortic aneurysm with very good sensitivity. Spinal infection or cancer patients will often have an elevated WBC and/or ESR or C-reactive protein, although none have the sensitivity nor the specificity to rule in or out these diseases. A urinalysis and creatinine is done for patients suspected of renal pathology. Blood cultures should be obtained prior to antibiotic administration for suspected spinal infection.
Any patient displaying signs or symptoms consistent with cauda equina syndrome should have a post-void residual preformed. After the patient has voided, a catheter is inserted into the bladder and the urine volume is measured. If the volume of urine is >200ml then this is considered a positive test and increases the suspicion for cauda equina. A post-void residual of <100ml makes the diagnosis less likely.
Plain X-rays of the spine should be obtained if ‗red flags‘ raise one‘s suspicion for cancer, infection or fracture. Specific indications for plain films include: age >70 years, unexplained weight loss, pain worse at rest, history of prolonged steroid use, cancer, IV drug use and osteoporosis. However, the sensitivity of plain films for spinal metastases is only 60%, while 17% of patients with epidural spinal cord
compression due to metastasis have normal X-rays. In addition, the overall sensitivity and specificity of plain X-rays for osteomyelitis or epidural abscess is 82% and 57% respectively.
CLINICAL PEARL
Any patient with a known history of malignancy with new onset of back pain should be
considered to have spinal metastases until proven otherwise.
All contents copyright © 2012, University of Toronto. All rights reserved It is thus incumbent upon the clinician who suspects
cauda equina syndrome to obtain an MRI of the spine as soon as possible. MRI is the imaging modality of choice for spinal cord compression. This is one of the few instances in which an MRI is indicated on an emergent basis. Plain CT of the spine may aid in the diagnosis since it can show bony detail, but like X-ray films, it does not have sufficient sensitivity and specificity to diagnose cauda equina and spinal cord compression syndromes with certainty. CT
Myelogram is an alternative option for patients who are unable to undergo MRI, however, it is an invasive procedure that has the potential to transmit infection into the subarachnoid space.