A 48-year-old obese man presents to the Physical Medicine and Rehabilitation (PM&R) clinic with new onset low back pain. He reports that low back pain, for years without clear onset that intermittently radiates into his right and left posterior thighs, is worse when standing and is associated with morning stiffness. However, he states that he had a sudden onset of back pain 3 weeks ago when he was moving furniture in his home. His pain is located at the lower back and radiates through his left leg. He characterizes his low back pain as cramping and aching and characterizes his left leg pain as burning and electric. His leg pain is worse with sitting and his back pain is worse when coughing. He takes an occasional Tylenol, which seems to help but only temporarily.
Review of Systems
He reports associated numbness at the plantar aspect of the left foot. He denies weakness. He denies bowel and bladder incontinence. He denies any weight loss, night sweats, or fevers.
Past medical history: He has a history of hypertension (HTN) for which he is taking Losartan 25 mg daily for the past 10 years.
Social history: Works as a lawyer, recently unemployed 6 months ago. He lives with his wife and two children on the fourth floor with an elevator. He ambulates without assistive device and is independent in his activities of daily living. He smokes 1 pack of cigarettes per day for the past 20 years. He does not drink alcohol or use intravenous drugs.
Allergies: No drug or environmental allergies
Medications: Losartan 25 mg daily, Tylenol as needed
BP: 140/70 mmHg, RR: 16/min, PR: 80 per min, Temp: 97° F, Ht: 5’6”, Wt: 220 lbs, BMI 35 kg/m 2
Head, eyes, ear, nose, and throat (HEENT)-extraocular movements (EOMs) full, no ptosis
Physical Examination
General: He is alert and oriented. He is in moderate distress because of left-sided back pain.
Musculoskeletal and Neurologic Examination:
Lateral bending and extension is limited by pain, flexion of trunk is significantly limited by pain
Diffusely rigid and tender to palpation along middle and lower paraspinal muscles
Motor examinaton: right and left lower extremities 5/5
Bilateral Achilles tendon reflex and bilateral patella tendon reflex 2+. Plantar reflex is down-going bilaterally. No clonus bilaterally.
Sensory examination: Dull to light touch along the left lateral thigh, lateral calf, and dorsum of foot. Normal sensation along right lower extremity.
Straight leg test is positive on the left side and negative on the right side
Gait is normal
General Discussion
The approach to a patient with lower back pain (LBP) generally involves categorizing distinct sources of back pain: axial, radicular, and referred pain. Axial lumbosacral pain involves the lumbar region, L1‒L5 vertebral segments, and sacral region, S1 to sacrococcygeal region. Axial back pain is commonly used to describe LBP associated with degenerative disc disease without compromise of neural elements. Radicular pain involves radiation of pain that travels through the leg along a dermatomal distribution consistent with a nerve root, or dorsal root ganglion, level compromise, most commonly secondary to mechanical compression. Referred back pain involves pain that travels from a source in a nondermatomal distribution along elements of the same mesodermal origins. Although these terms attempt to simplify etiologies of LBP, LBP is largely a multifactorial condition, including multiple physiologic and psychosocial factors that remain difficult to define, diagnose, and treat.
Once categorized, the determination of potentially progressive or unstable etiology of back pain is paramount ( Table 2.1 ). “Red flags” are used to determine such etiologies, including cancer, infection, trauma, and neurologic compromise. These findings include fevers/night sweats/chills, bowel or bladder incontinence, “saddle anesthesia” (decreased sensation around the perineum, groin, and/or medial thighs), thoracic pain, gait ataxia, or prior history of cancer or high impact trauma. Positive findings should prompt emergent evaluation, either via imaging and/or referral to specialists (surgery, oncology, etc.).
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As with any evaluation, a thorough history and physical examination are essential in diagnosis of lumbosacral radiculopathy. Regarding history, a complete description of pain is necessary, including onset, location, duration, characterization, alleviating and aggravating factors, radiation, timing, and severity. Associated paresthesias, such as numbness, tingling, and weakness, can often be appreciated as well. Of significant importance is associating these symptoms to a specific dermatomal and/or myotomal level for radicular back pain, requiring focal questioning ( Fig. 2.1 ). Regarding physical examination, a comprehensive neurologic examination is necessary, including assessment of motor strength and evaluation for upper motor findings ( Fig. 2.2 ). In addition, certain special maneuvers can guide to specific etiologies of low back pain as discussed earlier, such as facet loading test (axial back pain, facet arthropathy), straight leg raise and Slump test with reproduction of symptoms (radicular back pain, L4 to S1 radiculopathy), reverse straight leg raise, and Ely test with reproduction of symptoms (radicular back pain, ‒L4 radiculopathy; Table 2.2 ).
| Nerve Root | Pain Radiation | Gait Deviation | Motor Weakness | Sensory Loss | Reflex Loss |
|---|---|---|---|---|---|
| L3 | Groin and inner thigh | Sometimes antalgic | Hip flexion | Anteromedial thigh | Patellar (variable) |
| L4 | Anterior thigh or knee, or upper medial leg | Sometimes antalgic Difficulty rising onto a stool or chair with one leg | Knee extension, hip flexion and adduction | Lateral or anterior thigh, medial leg, and knee | Patellar |
| L5 | Buttocks, anterior or lateral leg, dorsal foot | Difficulty heel walking; if more severe, then foot slap or steppage gait Trendelenburg gait | Ankle dorsiflexion, foot eversion and inversion, toe extension, hip abduction | Posterolateral thigh, anterolateral leg, and mid-dorsal foot | Medial hamstring (variable) |
| S1 | Posterior thigh, calf, plantar foot | Difficulty toe walking or cannot rise on toes 20 times | Foot plantar flexion | Posterior thigh and calf, lateral and plantar foot | Achilles |
Differential Diagnosis
- 1.
Myofascial pain— most commonly localized to the low back. There may be radiation to the bilateral lower extremities along the posterior buttocks and thighs. This referral of pain is not consistent with a dermatomal distribution, and should not be mistaken for radiculopathy.
- 2.
Degenerative spine disease
Discogenic pain: Most commonly associated with low back pain worse with flexion, sitting, twisting, and increased abdominal pressure (coughing, sneezing).
Facet arthropathy: Most commonly associated with extension and lateral bending. Classically associated with facet-loading test positive; however, studies have shown it is unreliable in diagnosing facet arthropathy mediated pain alone.
- 3.
Lumbosacral radiculopathy— most commonly associated with leg pain, oftentimes will supersede lumbar pain, such that patients will experience leg pain greater than back pain. This pain usually radiates in a dermatomal fashion, associated with the pathologic nerve root.
- 4.
Lumbar stenosis— can present with low back pain, neurogenic claudication (discomfort, pain, numbness or weakness in the calves, buttocks, or thighs that is precipitated in lumbar extension and relieved in lumbar flexion), sensory disturbances in dermatomal and nondermatomal fashion, motor weakness, and pathologic reflexes.
- 5.
Lumbar postlaminectomy syndrome— commonly described as “failed back surgery syndrome”; it is defined by International Association for the Study of Pain as “lumbar spinal pain of unknown origin either persisting despite surgical intervention or appearing after surgical intervention for spinal pain originally in the same topographic location.” Comprehensive history should include evaluation of preoperative risk factors (psychosocial factors, smoking, obesity), intraoperative risk factors (operating at a single level, operating at the wrong level), and postoperative risk factors.
- 6.
Other causes of low back pain:
- a.
Cauda equina syndrome: Constellation of symptoms indicating neurologic compromise related to dysfunction of the ropelike nerve fibers at the distal spinal cord, most commonly caused by large lumbar disc prolapse with compression. These symptoms include, but are not limited to, saddle anesthesia, sexual dysfunction, fecal incontinence, bladder dysfunction, and lower limb weakness. Magnetic resonance imaging (MRI) is the choice of imaging, and treatment is urgent surgical decompression unless medically contraindicated.
- b.
Tumor: The strongest risk factor for back pain secondary to bone metastasis is a history of cancer. Those cancers associated with bone metastasis include breast, lung, renal cell, and prostate cancers.
- c.
Infection: A comprehensive history of infection related to low back pain includes recent fevers, malaise, spinal injections, epidural catheter placement, intravenous drug use, and immunosuppression.
- d.
There are numerous other causes of nonspine-related back pain, including fibromyalgia, piriformis syndrome, hip osteoarthritis, and aortic aneurysm
- a.
Case Discussion
Our patient presents with acute on chronic low back pain. In evaluating this patient, it is important to delineate his separate pain complaints. On one hand, he describes insidious onset of low back pain, which suggests chronicity. Given his chronic description of aching pain in the low back without dermatomal radiation, risk factors of obesity and smoking, physical examination findings of paraspinal tenderness and rigidity, this patient likely has axial back pain. Therefore differential diagnoses should include those associated with degenerative spine changes, such as discogenic disease, facet arthritis, and spondylosis.
On the other hand, he describes clear onset of pain after an inciting incident, which suggests acuity. Along with history of pain and numbness along L5 dermatome and physical examination findings of positive straight leg test, this patient likely has lumbosacral radiculopathy as well. Therefore differential diagnoses should include space occupying lesions resulting in compression of the L5 nerve root from the central canal to the neural foramen, including disc herniation, degenerative spondylosis, neural foraminal stenosis, and fractures.
Diagnostic Testing
In the absence of red flags, trauma, prior spinal surgery, and refractory back pain to conservative management, diagnostic testing is not indicated in the majority of patients with low back pain. Initial treatment should be geared toward conservative management.
Presently, there is no one type of imaging that shows a clear advantage over others. X-rays are a simple, cost-effective method of evaluation of bony anatomy to reveal gross bony abnormalities commonly associated with degenerative spine disease (such as disc space narrowing, osteophyte formation, neuroforaminal stenosis, facet arthropathy), misalignment (spondylolisthesis), and trauma (vertebral fractures, pars interarticularis fractures). X-rays are commonly used for chronic, persistent low back pain with acute pain associated with new red flags secondary to trauma, including fracture or instability. Flexion and extension views are recommended to evaluate symptomatic spondylolisthesis.
In patients with refractory radicular pain syndrome (radicular low back pain lasting 4–6 weeks after conservative management), MRI is considered the gold standard for imaging given its sensitivity for soft tissue evaluation, including disc, tumor, muscle, and nerve involvement. Of note, it is important to evaluate MRI with a high pretest probability, garnered from a precise clinical suspicion based on history and physical examination. Lumbosacral MRI examinations are more likely to be “abnormal” by age 40 years in asymptomatic individuals, and herniated discs are not infrequently found in asymptomatic young adults.
For patients who cannot undergo MRI, computed tomography (CT) remains an alternative option. Although routine CT is not recommended for acute, subacute, or chronic nonspecific or radicular low back pain, CT is recommended for patients with refractory radicular pain who are in consideration for epidural steroid injections. If these patients are in consideration for surgical discectomy or have a history of prior spinal surgery with hardware, CT myelography is recommended.
Bone scans can be used to evaluate for osteomyelitis, occult fractures, and inflammatory arthropathy. Single-photon emission CT (SPECT) imaging has also been used to evaluate inflammatory arthropathy, specifically that of the sacroiliac (SI) joint; however, SPECT imaging is not currently recommended for low back pain evaluation. Although discography, when paired with MRI or CT, can provide anatomic information for surgical decisions regarding discectomy for significant radiculopathy, the lack of standardization in discography leads to low predictive value and is currently moderately not recommended for evaluation of acute, subacute, and chronic low back and radicular pain.
Electrodiagnostic studies (EDX), primarily electromyography (EMG), can be used to evaluate radicular pain syndromes. It can be useful to determine if neurologic compromise is present, chronicity of symptoms, and/or aggravation of preexisting injury. However, it is important to note that EDX tests only motor axonal loss or conduction block, and would not yield abnormalities affecting the sensory nerve root. Therefore EDX is not recommended for low back pain without radicular pain symptoms. In addition, EMG represents a high specificity, low sensitivity test for radiculopathy, serving as a good way to confirmatory test rather than a screening test. Therefore it is important to use EDX studies as a supplement to clinical decision making and EDX results are interpreted in the realm of prevalence of suspected pathology.
Case Discussion
Our patient presents with radicular low back pain syndrome. Although he has not completed any conservative management, he does have a history of an inciting, traumatic event. Therefore imaging with X-rays would not be unreasonable.
Because our patient does not exhibit constitutional symptoms, neurologic compromise on examination, or red flags, further diagnostic testing is not indicated. Although MRI would not be necessary at this time, it could yield important information regarding further treatment options, such as interventional management.
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