Low Back Pain Case File

Low Back Pain Case File

Eugene C. Toy, MD, Barry C. Simon, MD, Terrence H. Liu, MD, MHP, Katrin Y. Takenaka, MD, Adam J. Rosh, MD, MS

Case 35

A 57-year-old man presents to the emergency department (ED) with a 1-month history of worsening low back pain. The pain radiates down the back of both legs and suddenly increased yesterday. For the past 2 days, the patient has been having difficulty voiding and has had “to force the urine out.” He has also noticed that the skin around his anus feels numb when he wipes with toilet tissue. He has worked in a warehouse for 30 years but has been on light duty for the past month due to his back pain. He denies prior trauma to or surgery on his back.

⯈ What is the most likely diagnosis?

⯈ What is the next diagnostic step?

ANSWER TO CASE 35:

Low Back Pain

Summary: A 57-year-old warehouse worker has a 1-month history of worsening low back pain with radiation bilaterally to his legs. The pain increased suddenly and is now associated with perianal numbness and difficulty voiding. He denies trauma to his back or prior surgery.

• Most likely diagnosis: Cauda equine syndrome (CES)
• Next diagnostic step: Magnetic resonance imaging (MRI) of the lumbar and sacral spine

ANALYSIS

Objectives

1. Review the possible etiologies of low back pain.
2. Learn how to evaluate a patient with low back pain.
3. Identify the “red flags” associated with serious causes of low back pain.

Considerations

Low back pain is a common complaint and can be caused by a multitude of disease processes. Although benign mechanical causes are most common, the ED physician must consider the “cannot miss” diagnoses: cauda equina syndrome, spinal fracture, spinal infection (epidural abscess or spondylitis), and malignancy. A careful history and physical examination are important to identify “red flags” that may herald the presence of serious disease (Table 35–1). Most patients with back pain do not

require any diagnostic studies in the ED. However, if a serious etiology is suspected, laboratory studies and imaging may be necessary. In general, pain control is a high priority for these patients. If the patient is critically ill, stabilization of the ABCs and surgical consultation may be needed.

Approach To:

Low Back Pain

CLINICAL APPROACH

Back pain is the second most common complaint that impels people to visit their primary care physicians. Seventy to ninety percent of adults suffer from acute low back pain during their lifetime. The differential diagnosis of low back pain is extensive. Common causes include muscle strain, ligamentous injury, osteoarthritis, disk herniation, spondylolisthesis, and fracture. Infectious etiologies are epidural abscess, spondylitis, diskitis, and herpes zoster. Malignancies that cause low back pain may be primary or, more commonly, metastatic. Rheumatologic diseases such as ankylosing spondylitis and Reiter syndrome are other considerations. Back pain may also be referred from various gastrointestinal, genitourinary, gynecologic, and vascular sources (most ominously from an abdominal aortic aneurysm). Miscellaneous causes include sickle cell pain crisis and functional back pain.

The history and physical examination are important to distinguish benign causes from potentially life-threatening ones. Table 35–2 describes the typical findings for patients with the “cannot miss” causes of low back pain. Important historical questions include location, duration, and onset of pain; aggravating and alleviating factors; associated symptoms; work history; history of trauma; and past medical history (including comorbidities, medications, and family history).

The ED physician should note the patient’s vital signs because any abnormalities may herald a life-threatening disease process (eg, hypotension due to sepsis or a ruptured abdominal aortic aneurysm). The physical examination should screen for signs of systemic disease and possible sources of referred back pain. If possible, gait and range of motion of the back should be observed. Inspection of the back can identify bony abnormalities such as scoliosis and skin lesions that suggest infection (erythema, warmth) or trauma (swelling, ecchymosis). The back should be palpated to isolate the area of maximal tenderness. Point tenderness over the spinous processes may indicate a destructive lesion of the spine. Pain that is severe or excessive has increased suspicion of acute spinal infection or AAA. The neurologic examination should focus on identifying any focal weakness, dermatomal sensory loss, and decreased or absent deep tendon reflexes. Straight-leg raise (SLR) testing involves the examiner passively elevating the supine patient’s leg (with knee extended) 30 to 70 degrees. If the SLR elicits radicular pain in the low back radiating down the leg to below the knee, it is indicative of sciatic nerve root irritation. This test is more sensitive (80%) than specific (40%). A positive crossed SLR (elevation of the unaffected leg causes radicular pain in the affected leg) is very specific (90%) but insensitive (25%). Digital rectal examination should

Abbreviations: CT = computed tomography; MRI = magnetic resonance imaging; CBC = complete blood count;

ESR = erythrocyte sedimentation rate.

be performed on patients with severe pain or neurologic deficits to assess sphincter tone and perianal sensation.

Most patients who present with low back pain do not require any diagnostic tests or imaging studies in the ED. The history and physical examination can help separate the majority of patients with simple, self-limited musculoskeletal back pain from the minority with more serious underlying causes. If rheumatologic causes, malignancy, or infection are concerns, a complete blood count, erythrocyte sedimentation rate, and urinalysis may be helpful. Indications for plain x-rays include age less than 18 years or older than 50 years; recent trauma; history or suspicion of malignancy; pain lasting longer than 4 to 6 weeks; history of fever, intravenous drug use, or immunocompromised; and progressive neurologic deficits. Further imaging by computed tomography or magnetic resonance imaging may be required if a strong suspicion of fracture, spinal infection, malignancy, or cauda equina syndrome exists.

Treatment

If a patient with low back pain is hemodynamically unstable, cardiac monitoring and resuscitation with intravenous fluids is mandated. If infection is suspected, antibiotics should be administered. Stable patients benefit from pain management. Depending on the severity of the pain, intravenous narcotics such as morphine or fentanyl may be required. If the pain is less severe, oral narcotics or nonsteroidal anti-inflammatory drugs (NSAIDs) may be sufficient. Benzodiazepines may be useful adjuncts to provide some muscle relaxation and sedation.

Patients with simple musculoskeletal back pain can be treated with pain control (primarily acetaminophen and NSAIDs). Oral narcotics may be used for a short period of time if the pain is not adequately controlled by the aforementioned medications. Application of local heat or ice may provide some pain relief. Although strict bed rest was once the recommended treatment, resumption of normal daily activities has been shown to hasten recovery and resolution of pain. Strenuous exercise should be avoided until the acute pain has subsided. Nearly all patients recover with conservative management within 4 to 6 weeks.

Admission should be considered for patients with underlying etiologies that require inpatient management, those with abnormal vital signs, those requiring intravenous narcotics for pain control, and those who cannot walk.

COMPREHENSION QUESTIONS

35.1 Which of the following describes the most common location of herniated disc of the lumbar spine region?

A. L1-L2

B. L2-L3

C. L3-L4

D. L4-L5

35.2 Which of the following is the most sensitive finding for cauda equina syndrome?

A. Decreased anal sphincter tone

B. Saddle anesthesia

C. Urinary retention

D. Weakness or numbness in the low extremities

35.3 A 27-year-old woman with a 1-week history of progressive pain radiating from the lumbar spine down the back of the leg presents to the ED. Her physical examination is normal except for complaints of back pain with movement. Which of the following is the most appropriate imaging test?

A. No imaging is necessary; attempt conservative therapy.

B. Obtain plain films of the lumbar spine.

C. Perform MRI.

D. Perform CT.

ANSWERS

35.1 D. The L4-L5 interspace is the most commonly affected.

35.2 C. Urinary retention with overflow incontinence is the most sensitive finding for cauda equina syndrome (90%).

35.3 A. No imaging is necessary. If the patient has no risk factors in the history and physical examination for serious disease other than sciatica, treat conservatively and do not perform any diagnostic tests in the ED.

CLINICAL PEARLS

⯈ Most patients with acute low back pain have resolution of symptoms within 4 to 6 weeks.

⯈ Pain that interferes with sleep, significant unintentional weight loss, or fever suggests an infectious or neoplastic cause of back pain. Low back pain with associated bowel and bladder dysfunction is suspicious for cauda equina syndrome.

⯈ Most patients do not require diagnostic tests or imaging studies. However, further testing may be advisable if there is a concern for rheumatologic, infectious, neoplastic processes; fracture; or cauda equina syndrome.

⯈ Pain control is important in the management of patients with low back pain. Acetaminophen, NSAIDs, and narcotics are all viable options.

References

Deyo RA, Weinstein JN. Low back pain. N Engl J Med. 2001;344:363-370. 

Frohna WJ, Della-Giustina D. Neck and back pain. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York, NY: McGraw-Hill; 2011; Chapter 276. 

Hermance TC, Boggs LR. Chapter 19: Arthitis and back pain. Stone CK, Humphries RL: Current Diagnosis and Treatment: Emergency Medicine. 6th ed. Available at: http://www.accessmedicine.com/content. aspx?aID=3100883. 

Jarvik JG, Deyo RA. Diagnostic evaluation of low back pain with emphasis on imaging. Ann Intern Med. 2002;137:586-597. 

Marx JA, Hockberger RS, Walls RM, eds. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 6th ed. Philadelphia, PA: Mosby Elsevier; 2006:260-268, 701-717. 

Morris EW, Di Paola M, Vallence R, Waddell G. Diagnosis and decision making in lumbar disk prolapse and nerve entrapment. Spine. 1986;11:436.

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