Low Back Pain

Differential Overview

❑ Musculoligamentous strain

❑ Lumbar disc herniation

❑ Osteoarthritis

❑ Compression fracture

❑ Pyelonephritis

❑ Secondary gain

❑ Scoliosis

❑ Spondylolisthesis

❑ Metastatic cancer

❑ Spinal stenosis

❑ Transverse process fracture

❑ Pancreatic cancer

❑ Ankylosing spondylitis

❑ Sacroiliitis

❑ Aortic dissection

❑ Cauda equina syndrome

❑ Vertebral osteomyelitis

❑ Epidural abscess

Diagnostic Approach

Radicular pain has such a high sensitivity for nerve root compression that its absence makes important disc herniation unlikely. Not all radicular pain is due to a herniated disc however. Other causes include spinal stenosis, ligamentous hypertrophy, deep lumbar muscle spasm, and deep trochanteric bursitis.

Back pain at rest or unassociated with posture/movement should increase the suspicion of tumor, fracture, infection, or referred visceral pain. Spinal tenderness is a sensitive but not specific indicator. Clues to metastatic cancer include a history of cancer, unexplained weight loss, and signs of cord compression, such as motor weakness of the legs, urinary or fecal incontinence, and absent anal reflex. Recent bacterial infection, injection drug use, or immune suppression (from steroids, chemotherapy, or HIV) should raise suspicion for infection. Fever occurs in osteomyelitis (50%), epidural abscess (83%), and tuberculosis (27%).

A red flag for fracture in a young adult is major trauma, such as a fall from a height or a motor vehicle accident. In older adults, minor trauma or strenuous lifting can cause a compression fracture.

Clinical Findings

Musculoligamentous strain  Strain usually occurs after episodic or repetitive lifting, bending, or twisting. Pain may radiate from the low back into the buttock or posterior thigh but not below the knee. There may be visible or palpable paraspinous spasm. Reproduction of the injury-inducing movement sharply exacerbates the pain.

Lumbar disc herniation  Pain, numbness, or paresthesia radiating in a dermatomal pattern from the back into the foot is the hallmark of this syndrome. L4, L5, and S1 roots are affected in more than 95% of cases. L4 compression (L3-4 disc) produces neuritic symptoms in the instep of the foot. Motor weakness of foot inversion and a diminished knee reflex may also occur, but these are not invariable findings and are better considered indicators of severity. L5 compression produces symptoms in the dorsum of the foot, weakness of great toe extension, and no reflex changes. S1 compression causes symptoms in the lateral foot and heel, weakness of foot eversion, and a diminished ankle reflex. Straight leg raising, which stretches the nerve roots, reproduces pain or numbness radiating into the foot. Pain may be increased further by dorsiflexion of the foot with the leg elevated. Care must be taken not to overinterpret muscular spasm from stretching the low back or tight hamstrings as a positive test. Positive crossed straight leg raising (radicular pain in the leg opposite to that being raised) suggests a large disc or extruded disc fragment. Rarely, herniation of a higher disc (L3) will produce pain in the anterior thigh, quadriceps atrophy, and positive reverse straight leg raising (patient prone).

Osteoarthritis  It is recognized as pain and stiffness with flexion and rotation in a patient with evidence elsewhere of osteoarthritis (e.g., Heberden and Bouchard nodes). Hypertrophied facets, osteophytes, and/or spondylolisthesis may cause root compression.

Compression fracture  Related to osteoporosis, it occurs mostly in older patients and those on steroids. Sudden-onset pain brought on by flexion stress is the usual history. Pain is localized over the vertebrae or around the trunk, and there often is tenderness to palpation over the spinous processes. The upper lumbar or lower thoracic vertebrae are most commonly affected. Consider metastatic cancer, myeloma, and hyperparathyroidism as alternative causes.

Pyelonephritis  Renal infection presents with fever, prominent nausea, chills, urinary frequency, and costovertebral angle pain and tenderness.

Secondary gain  Clues are inconsistent symptoms or physical findings (they change and lack an anatomic distribution), anger, focusing on attribution of symptoms with relatively less concern about what can be done to cure the problem, and impending litigation.

Scoliosis  Functional scoliosis disappears with flexion while structural scoliosis increases.

Spondylolisthesis  This is often asymptomatic, but when symptoms occur, flexion and extension of the low back is painful, and motion is limited. A palpable shelf may be present at the level of the defect and increases with flexion.

Metastatic cancer  Back pain is of insidious onset, is not relieved by lying down, often occurs at night, and is described as “boring” or “expansile.” A history of cancer and unexplained weight loss are specific findings. Myeloma, prostate, breast, lung, and colon cancers are common sources.

Spinal stenosis  Stenosis occurs most commonly in elderly patients as chronic low back pain with evidence elsewhere (hands or knees) of osteoarthritis. The pain is worsened by standing without walking (unlike claudication) and relieved by sitting (unlike disc disease) or flexing the spine and hips. The pain may radiate into the legs and is often bilateral and poorly localized.

Transverse process fracture  Its origin is violent muscular contraction of the psoas. There is exquisite tenderness lateral to the spinous process. It may be associated with retroperitoneal bleeding leading to hypovolemic shock.

Pancreatic cancer  This cancer presents insidiously with relentless, dull upper lumbar backache with abdominal pain. Weight loss and depression are prominent.

Ankylosing spondylitis  It occurs in young men, presenting with gradual onset of back stiffness, especially in the morning. Active or old iridocyclitis (iridic adhesions or dark spots in the anterior chamber), arthritis, and a prior history of inflammatory bowel disease are clues. The Schober maneuver revealing limited flexion is sensitive but not specific.

Sacroiliitis  The sacroiliac joints, marked by the sacral dimples, are deeply tender.

Aortic dissection  Acute onset, moving, tearing back pain, a restless and “shocky” patient, asymmetric femoral pulses, abdominal pulsation, and an abdominal bruit are key findings.

Cauda equina syndrome  Urinary retention or overflow incontinence, saddle anesthesia, bilateral leg weakness/numbness, and anal sphincter laxity are found. Ankle jerks are decreased, but knee jerks are increased (due to unopposed quadriceps). It is most commonly caused by a herniated disc.

Vertebral osteomyelitis  Low-grade fever, dull, continuous, and progressive back pain, and tenderness to percussion over the spine are found.

Epidural abscess  The characteristic presentation is radicular pain or progressive muscular weakness in a febrile patient with localized back pain and tenderness, particularly percussion tenderness. The pain is increased with recumbency, sudden movements, or Valsalva. Lhermitte sign, an electric-like sensation shooting down the back, is often present. Early signs of impending paraplegia include extensor plantar reflex (toes pointing downward), leg weakness, and urinary retention.

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Book Source Details

• Book Title: Field Guide to Bedside Diagnosis
• Author(s): David S. Smith
• Year of Publication: 2007
• Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2007 Lippincott Williams & Wilkins.

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Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2008 Williams & Wilkins.

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More About This Book: Title: Field Guide to Bedside Diagnosis Authors: David S. Smith Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-78178-165-5

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