A 42-year-old man presented to a pain management specialist with low back and leg pain that began after lifting a heavy object. The pain started in the middle of his lower back and radiated down the back of his right leg into the sole of his right foot. The pain was not relieved with acetaminophen and bed rest. Magnetic resonance imaging (MRI) of the lumbar spine showed a herniated disk at the L5-S1 level with impingement of the S1 nerve root. The patient was otherwise in excellent health.
What is the incidence of low back pain?
Low back pain with or without radiculopathy (pain or abnormal neurologic function caused by pressure on or irritation of a spinal nerve) is the second most common reason patients visit a physician and accounts for 3% of all hospital discharges. During their lifetime, 80% of the U.S. population experience low back pain, and it has been estimated that at any time approximately 15% of Americans have low back pain. Back pain affects patients of all ages; elderly adults have more severe pain and pain of longer duration.
What is the differential diagnosis of low back pain?
Low back pain can be caused by a multitude of pathologic processes. Although most cases of low back pain are of muscular or spinal origin, many intraabdominal and lower thoracic pathologies can refer pain to the low back. Examples include pancreatic cancer, lower lobe pneumonia, and aortic aneurysms.
For a structure in the spine to cause pain, it must be innervated, subject to possible injury or irritation, and in theory, the pain should be reversible with local anesthetic blockade of the structure. The most common cause of low back pain is believed to be myofascial pain, or muscular in origin. Other common causes of low back pain include internal disk disruption (IDD), sacroiliac (SI) joint pain, and pain from facet joint arthropathy. Lumbar stenosis, which causes narrowing of the spinal canal, is a common cause of low back pain, especially in elderly patients, as is lumbar degenerative disk disease and spondylosis. Less frequent skeletal causes include metabolic (osteoporosis), neoplastic (primary or metastatic), infectious (osteomyelitis, epidural abscess), traumatic (fractures), and congenital (scoliosis) conditions. Rheumatoid and other types of inflammatory arthritis can also cause low back pain.
A herniated disk (herniated nucleus pulposus) usually causes pain or other neurologic dysfunction down the leg. Back pain and leg pain of neurologic origin may also originate from irritation of nerves by spinal osteophytes; tumors in the pelvis or near the spinal column; or diseases of the neuraxis, such as inflammation (herpes zoster) or neoplasms (intradural or epidural tumors).
Because of the large differential diagnosis, a thorough investigation and evaluation is necessary to determine the cause of lower back pain. Although it is easy to rule out many factors that may cause pain, the exact etiology of pain often is difficult to determine, especially when dealing with nonradicular pain.
Discuss the evaluation of a patient with low back pain.
Low back pain must be evaluated and managed the same way as any other presenting complaint. Although most cases of low back pain resolve with conservative treatment, back pain lasting >1 month requires a complete clinical evaluation, consisting of a full history, physical examination, and interpretation of laboratory data. The history should concentrate on the characteristics and location of the pain and a review of modifying factors. Associated factors, such as leg weakness or changes in bladder or bowel function, need to be elicited. A full medical and surgical history and complete review of systems are required. While performing a physical examination that concentrates on the lower back and lower extremities, a differential diagnosis of the cause of pain should be obtained. Before any intervention on the spine, lumbosacral MRI or computed tomography (CT) scan should be obtained to rule in a diagnosis and to rule out rarer sources of pain, such as a malignancy or epidural abscess.
What is the classic presentation of a patient with a herniated nucleus pulposus?
The average age of patients presenting with a herniated disk is 30–50 years. Although pain from a herniated nucleus pulposus (herniated disk) may start after trauma, such as lifting a heavy object, it also can occur without any obvious inciting event. Depending on the nerve root involved, the dermatomal distribution of pain may be in the back of the leg (lower lumbar disks) or in the groin or anterior thigh (upper lumbar to midlumbar disks). The pain and occasionally accompanying neurologic dysfunction may be caused by mechanical compression of nerve roots or more likely by chemical inflammation from substances released from degenerating intervertebral disks (e.g., phospholipase A, bradykinin, histamine). The pain is usually aggravated by bending, coughing, or sneezing and is improved with resting and lying down. Rarely, bowel or bladder dysfunction can occur. CT scan or MRI is invaluable in confirming the diagnosis. However, imaging must be correlated with clinical symptoms, because positive findings on imaging may not be related to the present symptoms. Approximately 30% of asymptomatic adults have abnormalities on lumbar MRI.
Physical examination demonstrates increased pain when tension is applied to the lumbosacral plexus. Tests such as the bowstring sign (radicular pain elicited by popliteal pressure with the hip flexed and knee extended) and the LasÃ¨gue test (radicular pain secondary to foot dorsiflexion with the leg extended) are indicative of nerve irritation.
Sensory deficits may manifest over the dermatomal distribution of the involved nerve. Reflex testing of L4 radiculopathy may show a decreased response to the knee reflex, whereas S1 radiculopathy may show a decrease in the Achilles reflex. Motor deficits over the respective nerve root may also occur; for example, L5 radiculopathy may cause weakness of dorsiflexion of the foot.
Differentiate the clinical presentation of a patient with a herniated nucleus pulposus from a patient with spinal stenosis.
Spinal stenosis, which is primarily seen in older patients, is caused by narrowing of the central spinal canal or the lateral neuroforamen by a combination of enlarging posterior facet joints, osteophytes from osteoarthritis, hypertrophy of the ligamentum flavum, and bulging of the disk anulus. These structures may impinge on nerve roots or the cauda equina and produce typical radicular pain, although patients with spinal stenosis may also present with nonradicular low back pain. Patients with spinal stenosis may experience neurogenic claudication, which is leg pain while walking that is relieved by sitting and resting. Neurogenic claudication differs from vascular claudication in that the sitting position relieves the pain in the former condition, and cessation of walking relieves the pain in the latter condition.
Pain from spinal stenosis differs from the pain of a herniated disk in that flexion of the lumbar spine relieves spinal stenosis pain. Disk disease pain is typically relieved by reclining and may be increased with flexion of the lumbar spine. Another difference between spinal stenosis and disk disease is that pain and neurologic deficits can extend over several dermatomes with spinal stenosis because of the diffuse nature of the disease. A herniated nucleus pulposus usually manifests as a localized disease of a limited dermatomal distribution. Spinal stenosis is characterized by chronic, mild discomfort that progresses over time. Conversely, the hallmark of disk disease is the acute and severe onset of radicular pain ( Table 69-1 ).