Differential Diagnosis of Low Back Pain

“Physicians think they do a lot for a patient when they give his disease a name.”

—Immanuel Kant (1800)

This question is frequently asked by doctors at various stages of training and practice experience: “How can I assess and treat a patient with back pain when the diagnosis is so elusive?” It is hard on the ego to assess a patient and fail to arrive at a concrete diagnosis on which to base a treatment program. The result often is a treatment program based more on hope than science. This should not be so. In today’s medical world, our clinical skills and our investigative tools are such that we should be able to arrive at the correct diagnosis for most patients with “lumbago or sciatica.” This chapter outlines the simple steps needed to assess a patient who presents with a complaint of low back pain.

Assessment Method

Do not initiate your assessment with a long list of time-consuming differential diagnoses on your menu. In family practice, this presents an overwhelming burden to the multitude of chief complaints heard during a day. Instead, adopt a simple, methodical approach. Your goal is to sort those patients who have mechanical or structural problems in the low back from those who have not. In a family practice setting, perhaps 20% to 25% of patients presenting with low back pain will have a source outside of the back as the cause of their symptoms. This fact presents many pitfalls for the unwary. For this reason, accurate evaluation requires a logical, step-by-step method. The foundation of this method is the clinical assessment/the good old-fashioned history and physical examination. Investigations such as computed tomography (CT) scanning and magnetic resonance imaging (MRI) should play a secondary role to clinical assessment. Today, our investigative tools are so sophisticated that one can find pathology on investigation in almost every patient whether or not the patient is sick (1,2). Moreover, minor insignificant pathology can become the red herring that causes you to miss the symptom producing lesion.

The Clinical Approach

In assessing a patient with a low back complaint, ask yourself five questions:

Is this a true physical disability or is there a setting and a pattern on history and physical examination to suggest a nonphysical or nonorganic problem?
Is this clinical presentation a diagnostic trap?
Is this a mechanical low back pain condition, and if so, what is the syndrome?
Are there clues to an anatomic level on history and physical examination?
After reviewing the results of investigation, what is the structural lesion and does it fit with the clinical syndrome?

Although these questions may not be answered sequentially during the history and physical examination, they ultimately must be answered sequentially before arriving at a diagnosis and
prescribing a treatment program. That is to say, do not answer Question 5 and plan a treatment program until you have satisfactory answers to each preceding question. Probably the biggest pitfall is to answer Question 3 before you have satisfactorily answered Questions 1 and 2. The answers to Questions 1 and 2 should routinely be made outside the hospital, and before CT, myelography, MRI, and other sophisticated investigative modalities are used. The classic trap is to ignore Questions 1 and 2 and admit a patient with a complaint of low back pain to the hospital, with sophisticated investigative tools, and then prescribe a treatment plan based on false-positive findings.

Question 1

Is this a true physical disability, or is there a setting and a pattern on history and physical examination to suggest a nonphysical or nonorganic problem? That medicine should concern itself with the whole person is often stated but frequently ignored. The hallmark of a good clinician is the ability not only to diagnose disease but also to assess the “whole patient.” No test of the art of medicine is more demanding than the identification of the patient with a nonorganic or emotional component to a back disability.

Remember the disability equation:

Disability = A + B + C

where:

A = the physical component (disease).

B = the patient’s emotional reaction.

C = the situation the patient is in at the time of disability (e.g., compensation claim, motor vehicle accident).

Each patient presenting with a back disability may have some component of each of these entities entwined in their disability. For example, a patient presenting a collection of symptoms, with no physical disability evident on examination, should lead one to think of the other aspects of the equation and look for emotional disability or situational reactions.

A classification of nonorganic spinal pain is presented again in Table 14-1. The term nonorganic has been chosen over other terms such as nonphysical, functional, emotional, and psychogenic. The conditions classified in Table 14-1 are such a common part of practice you cannot remind yourself enough to consider them in your differential diagnosis.

Commit Table 14-2 to memory. If you are puzzled by a patient with a complaint of low back pain, revisit Question 1: Is this a true physical disability? Specifically look for some or all of these symptoms and/or signs. If they are present, stop! Do not order expensive tests and treatment but rather seek help from someone more skilled in the evaluation of these nonorganic syndromes.

It is important to stress that one swallow does not make a spring! The fact that a patient has one of these findings does not mean the patient should be classified as a exaggerator or litigant reactor. It is important to stress that a collection of symptoms and signs should be present
with the appropriate clinical setting to make the diagnosis of exaggeration behavior. Waddell et al. (3) have documented the significant symptoms and signs that, when collected together, suggest that a nonorganic component to a disability is present. These symptoms and signs have been scientifically documented as valid and reproducible. As a screening mechanism they are an excellent substitute for pain drawings and psychological testing.

TABLE 14-1 Classification of Nonorganic Spinal Pain

Psychosomatic spinal pain

Tension syndrome (fibrositis)

Pure psychogenic spinal pain

Psychogenic spinal pain

Psychogenic modification of organic spinal pain

Situational spinal pain

Litigation reaction

Exaggeration reaction

TABLE 14-2 Symptoms and Signs Suggesting a Nonorganic Component to Disability

Symptoms

Pain is multifocal in distribution and nonmechanical (present at rest)

Entire extremity is painful, numb, and/or weak

Extremity gives way (as a result, the patient carries a cane)

Treatment response:

A. No response

B. “Allergic” to treatment

C. Not receiving treatment

Multiple crises, multiple hospital admissions/investigations, and multiple visits to doctors

Signs

Tenderness is superficial (skin) or nonanatomic (e.g., over body of sacrum)

Simulated movement tests positive

Distraction tests positive

Whole leg weak or numb

Academy Award performance

Every human attends the school of survival. Sometimes the lessons lead patients to modify or magnify a physical disability at a conscious or unconscious level. Another word of caution: The presence of one of these nonorganic reactions does not preclude an organic condition such as a herniated nucleus pulposus. The art of medicine is truly tested by a patient with a physical low back pain who modifies the disability with a nonorganic reaction of tension, hysteria, depression, or emotional factors.

Question 2

Is this clinical presentation a diagnostic trap? It is too easy, when trying to arrive at a mechanical diagnosis, to fall into the many traps in the differential diagnosis of low back pain. An example is the young man in the early stages of ankylosing spondylitis who presents with vague sacroiliac joint pain and mild buttock and thigh discomfort who is thought to have a disc herniation. The patient with a retroperitoneal tumor invading the sacrum or sacral plexus may present with classic sciatica and also be diagnosed as having a disc herniation. It is not uncommon that patients with pathology within the peritoneal cavity will refer pain to the back. To avoid missing these various diagnostic pitfalls, always ask yourself the second question: Is this clinical presentation a trap?

Two broad categories of disease are included in this question:

Back pain referred from outside the spine may come from within the peritoneal cavity (e.g., gastrointestinal tumors or ulcers) or from the retroperitoneal space (genitourinary conditions, abdominal aortic conditions, or primary or secondary tumors of the retroperitoneal space). These patients can be recognized clinically on the basis of two historic points. First, the pain is often nonmechanical in nature and troubles the patient just as much at rest as it does with activity. Second, the pain in the back often has the characteristics of the pain associated with the primary pathology, that is, if the primary pain is colicky, the back pain will be colicky.
Painful, nondegenerative conditions arising from within the spinal column, including its neurologic content. This group is subdivided into the following:
- The differential diagnosis of low back pain or lumbago (Table 14-3).
- The differential diagnosis of radicular pain or sciatica (Table 14-4).

TABLE 14-3 Differential Diagnosis of Nonmechanical Low Back Pain

Referred pain (e.g., from the abdomen or retroperitoneal space)

Infection: bone, disc, epidural space

Neoplasm

Primary (multiple myeloma, osteoid osteoma, etc.)

Secondary

Inflammation

Miscellaneous metabolic and vascular disorders such as osteopenias and Paget’s disease

These patients have nonmechanical back pain or a pain characteristic for the primary pathology. Radiating extremity pain is not common unless neurologic territory has been invaded by the disease process, which usually occurs late in the disease. Unfortunately, many of these conditions are not obvious on history and physical examination and are often missed on reviewing plain radiographs. The following diagnostic tests are useful as a screening mechanism:

Hemoglobin, hematocrit, white blood cell count, differential, and erythrocyte sedimentation rate (ESR).
Serum chemistries, especially calcium, acid and alkaline phosphatase, and serum protein electrophoresis.
Bone scan. These three screening tests can be completed outside of the hospital and almost routinely identify these conditions. MRI will start to play a bigger role in the diagnosis of these various nonmechanical conditions.

TABLE 14-4 Differential Diagnosis of Sciatica

Intraspinal causes

Proximal to disc: conus and cauda equina lesions (e.g., neurofibroma, ependymoma)

Disc level

Herniated nucleus pulposus

Stenosis (canal or recess)

Infection: osteomyelitis or discitis (with nerve root pressure)

Inflammation: arachnoiditis

Neoplasm: benign or malignant with nerve root pressure

Extraspinal causes

Pelvis

Cardiovascular conditions (e.g., peripheral vascular disease)

Gynecologic conditions

Orthopaedic conditions (e.g., osteoarthritis of hip)

Sacroiliac joint disease

Neoplasms

Peripheral nerve lesions

Neuropathy (diabetic, tumor, alcohol)

Local sciatic nerve conditions (trauma, tumor)

Inflammation (herpes zoster)

Although the most common cause of leg pain in a radicular distribution is a structural lesion in the lumbosacral region, there are many other causes of radiating leg discomfort that must be considered. Missing these conditions is probably the most common error made in a spine surgical practice. For example, the high sensitivity of today’s investigative modalities is capable of showing a minor and insignificant herniated nucleus pulposus when, in fact, the patient has a conus tumor higher in the spinal canal (Fig. 14-1). This situation is being abetted by the tendency to perform a CT scan and skip myelography in an attempt to arrive at a structural diagnosis for mechanical low back pain. This may seem a good idea to avoid the complications of myelography, but it will present problems unless you adhere to the following rule: An equivocal CT scan requires completion of myelography. As more MRI is done, the issue is going to be resolved. Soon, all patients with low back pain who do not respond to usual conservative treatment measures will be mandated by government or an insurance clerk to have an outpatient hematologic and serum screen, a bone scan, a CT scan, or MRI. (Is it far down the road that one day robots will deal with the structural lesion?)

FIGURE 14-1 Gadolinium-enhanced sagittal MRI of high lumbar schwannoma that was not seen on initial unenhanced MRI.

Etiology of Radiating Leg Pain

Space does not permit discussion of all the differential diagnoses of radiating leg pain, but three common conditions must be recognized:

Cardiovascular conditions (peripheral vascular disease).
Hip pathology.
Neuropathies.

Cardiovascular conditions.

Cardiovascular disorders in the form of peripheral vascular disease can cause leg discomfort that is easily confused with nerve root compression. Because these conditions tend to occur in the older patient population, they may coexist. Table 14-5 separates vascular claudication from neurogenic claudication.

Hip Pathology.

Usually, it is easy to diagnose conditions of the hip because they so commonly cause pain around the hip and specifically pain in the groin. An early clue to hip pathology is the patient’s statement that he/she cannot comfortably put on his/her socks (external rotation) (Fig. 14-2). In addition, walking causes a limp, and physical examination reveals a loss of internal rotation early

in the disease. Occasionally, however, a patient with hip pathology will have no pain around the hip and will have only referred pain in the distal thigh. In these patients, it is easy to miss hip pathology unless one specifically examines the hip for loss of internal rotation. If there is any doubt, an radiograph of the hips must be taken, and if still in doubt a bone scan will be required.

FIGURE 14-2 A patient with hip disease has trouble getting his or her leg into position (hip externally rotated) to put on socks. A patient with an acute disc herniation cannot get socks on because he or she cannot even sit to try and get the leg into this position!

TABLE 14-5 Differential Diagnosis of Claudicant Leg Pain^a

Findings	Vascular Claudication	Neurogenic Claudication
Pain
Type	Sharp, cramping	Vague and variously described as radicular, heaviness, cramping
Location	Exercised muscles (usually calf and rarely includes buttock, almost always excludes thigh)	Either typical radicular or extremely diffuse (usually including buttock)
Radiation	Rare after onset	Common after onset, usually proximal to distal
Aggravation	Walking, especially uphill	Not only aggravated by walking, but also by standing
Relief	Stopping muscular activity even in the standing position	Walking in the forward flexed position more comfortable; once pain occurs, relief comes only with lying or sitting down
Time to relief	Quick (seconds to minutes)	Slow (many minutes)
Neurologic symptoms (Paresthesia)	Usually not present	Commonly present
Straight leg raising tests	Negative	Mildly positive or negative
Neurologic examination	Negative	Mildly positive or negative
Vascular examination	Absent pulses	Pulses present
^a Be wary of the patient in whom both conditions coexist.

Neurologic Disorders.

Someone who sees a lot of patients with low back pain will quickly realize that they must be a good neurologist. This is a major advantage of a neurosurgically trained spine surgeon over an orthopaedically trained spine surgeon. But all is not lost if one takes a simple step by step approach to the patient who presents with weakness, sensory upset, pain, and instability in the lower extremities. If pain is the predominant lower extremity symptom and follows a typical radicular distribution, there is a reasonable chance you are dealing with nerve root encroachment from a disc or osteophyte. But if weakness, sensory upset and/or instability is/are the dominant symptom(s), watch out: There is a good chance you are dealing with a primary neurologic disorder. How do you approach such a patient?

Weakness as a Symptom

Weakness comes in many forms. For the poor historian it is one of the first words they reach for to describe almost any problem with the legs. It is used to describe generalized fatigue regardless of cause, for example, anemia. A true motor weakness will affect one or both limbs or a muscle group and will originate in the motor unit or the proximal motor pathways in the spinal cord, brainstem, and cortex. Table 14-6 outlines the clinical aspects of weakness to help distinguish central from peripheral lesions. The next step in evaluating weakness is to separate the myopathies form the neuropathies. A good general rule is that the more proximal and symmetric the weakness, the more likely you are dealing with a myopathy. The more distal lesions, symmetric or asymmetric, are more likely polyneuropathies.

Only gold members can continue reading. Log In or Register to continue