Lower Back and Lower Limb Pain

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Chapter 30 Lower Back and Lower Limb Pain

Lower back pain is one of the most common reasons for neurological and neurosurgical consultation. The cost to society is huge, with estimates of up to $80 billion per year in direct and indirect healthcare costs and loss of productivity. In Switzerland, low back pain consumes 6.1% of the total healthcare budget and up to 2.3% of their GDP (Wieser et al., 2010). In many of the patients who present with lower back pain, the pain either developed or was exacerbated as a result of occupational activity. Lower limb pain is a common accompaniment to lower back pain but can occur independently.

The list of considerations in the differential diagnosis of lower back and lower leg pain is extensive and includes neural, bone, and non-neurological disorders. Although lower back pain usually is thought of as either neuropathic (specifically, radiculopathy-associated) or mechanical in origin, other possible sources of pain, including urolithiasis, tumors, and other intraabdominal processes, must be considered in the differential diagnosis.

Related Anatomy and Physiology

The lumbosacral spinal cord terminates in the conus medullaris at the level of the body of the L1 vertebra (Fig. 30.1). The motor and sensory nerve roots from the lumbosacral cord form the cauda equina. From there, the motor and sensory nerve roots unite at the dorsal root ganglion to form the individual spinal nerves. These anastomose in the lumbosacral plexus (Fig. 30.2), from which run the major nerves supplying the leg (Table 30.1).

Fig. 30.1 Oblique (A) and axial (B) views of the spine showing anatomical relationships between neural and bone elements.

Fig. 30.2 Anatomy of the lumbosacral plexus.

(Reprinted with permission from Bradley, W.G., 1974. Disorders of the Peripheral Nerves. Blackwell, Oxford, p. 29.)

Table 30.1 Motor and Sensory Function of Lumbosacral Nerves

Pain in the lower back can have many origins. A good beginning for the differential diagnosis is determining whether the leg also has pain. A complicating factor in this consideration is that local spine pain can be referred—that is, felt at a distance—because of the common nerve root innervation of the proximal spinal nerves and peripheral nerves supplying distal parts of the leg.

Causes of lower back pain without leg pain include:

Causes of lower back plus lower limb pain include:

Radiculopathy

Plexopathy

Important causes of leg pain without low back pain include:

Sciatic neuropathy

Femoral neuropathy

Peroneal neuropathy

Meralgia paresthetica

Peripheral neuropathies

Isolated tibial neuropathy is uncommon. Individual peripheral nerve lesions usually are caused by local trauma, entrapment by connective tissue, or involvement with mass lesions.

Lower back pain occasionally is caused by non-neurological and nonskeletal lesions. Some of the most important causes are:

Urolithiasis

Ovarian cysts and carcinoma

Endometriosis

Bladder or kidney infection

Abdominal aortic aneurysm

Diagnosis

The first step in diagnosis is localization of the causative lesion. History and examination usually allow differentiation among mechanical, neuropathic, and non-neurological pain.

History and Examination

The history should focus first on features of the back and leg pain:

Mode of onset

Character

Distribution

Associated motor and sensory symptoms

Bladder and bowel control

Exacerbating and remitting factors

History of predisposing factors (e.g., trauma, cancer, osteoporosis)

For example, the acute onset of lower back pain radiating down the leg suggests a lumbosacral radiculopathy. Onset with exertion suggests a herniated disk as a cause of the radiculopathy. Onset following a motor vehicle accident also could be associated with a disk herniation, although contusion of a nerve root without ongoing compression is more common after this type of trauma. Progressive symptom development can be from any expanding lesion, such as a tumor or expanding disk extrusion.

Patients with lower back and leg pain usually have more symptoms than signs of neurological dysfunction. Therefore, if examination shows sensory and motor signs in a specific radicular or neural distribution, a detectable structural lesion is more likely.

The neurological examination is targeted to determine whether the symptoms are accompanied by abnormal neurological signs. General examination of the lower limb is important. Muscle groups that can be tested include:

Sensory examination should include the important nerve roots and peripheral nerve distributions: the femoral, peroneal, tibial, and lateral femoral cutaneous, lumbar roots L2-L5, and sacral root S1. Reflexes to be studied include the Achilles, patellar, and plantar reflexes.

Exacerbation of pain with some maneuvers also can be revealing. Stretch of damaged nerves results in increased pain by deforming the axon membrane, thereby increasing membrane conductance, depolarizing the nerve, and producing repetitive nerve pain action potentials. Straight leg raising augments pain in a lumbosacral radiculopathy. Hip extension exacerbates pain of upper lumbar radiculopathy or that due to damage to the upper parts of the lumbar plexus, such as from carcinomatous infiltration or inflammation.

Armed with the abnormalities recognized from this history and examination, the neurologist may come to a conclusion about the localization of the lesion. This knowledge narrows the differential diagnosis substantially.

Differential Diagnosis of Lower Back and Leg Pain

The differential diagnosis of lower back and leg pain can be addressed as shown in Tables 30.2 through 30.5. Classification into mechanical and neuropathic categories is useful to narrow the scope of diagnostic considerations. The possibility of non-neurological causes should always be kept in mind.

Table 30.2 Classification of Lower Back and Lower Limb Pain

Type	Examples
Mechanical pain	Facet pain Bony destruction Sacroiliac joint inflammation Osteomyelitis Diskitis Lumbar spondylosis

Neuropathic pain

Polyneuropathy

Radiculopathy from disk disease, zoster, and diabetes

Mononeuropathy including sciatic, femoral, lateral femoral cutaneous, and peroneal neuropathies

Plexopathy from cancer, abscess, hematoma, and autoimmune processes

Non-neurologic pain

Urolithiasis

Retroperitoneal mass

Ovarian cyst or carcinoma

Endometriosis

Table 30.3 Differential Diagnosis of Lower Back and Leg Pain

Disorder	Clinical Features	Diagnostic Findings
Radiculopathy	Back pain radiating into leg in a dermatomal distribution. Sensory loss and motor loss are in a root distribution. Increased pain with coughing or straining.	Suspected when neuropathic pain radiates from back down into leg in a single root distribution. Disk or mass can be seen on MRI or CT. Zoster and diabetes can cause radiculopathy without abnormal studies.
Plexopathy	Back and leg pain with a neuropathic character, dysesthesias, burning, or electric sensation. Back pain can develop when cause is mass lesion in region of plexus.	Suspected when patient has leg pain in more than one peripheral nerve or root distribution. MRI of plexus or CT of abdomen and pelvis can show mass or hematoma.
Spinal stenosis	Pain in lower back, buttocks, and legs, especially with standing, walking, and lumbar spine extension.	MRI or CT shows obliteration of subarachnoid space.

CT, Computed tomography; MRI, magnetic resonance imaging.

Table 30.4 Differential Diagnosis of Isolated Lower Back Pain

Disorder	Clinical Features	Diagnostic Findings
Sacroiliac joint inflammation	Pain lateral to spine where sacrum inserts into top of iliac bone. Pain is exacerbated by movement and pressure but does not radiate down leg.	Clinical diagnosis. Radiographs can show degenerative changes in joint. Bone scan shows increased uptake in region.
Facet pain	Unilateral or bilateral paraspinal pain without radiation. Pain is increased by spine motion, especially extension.	Clinical diagnosis. Radiographs can show facet degeneration.
Ovarian cyst or cancer	Pain in hip and lower back, often but not always extending into lower quadrant. Bowel disturbance may develop with advanced disease.	Abdominal and pelvic CT shows mass lesion in ovary.
Endometriosis	Usually pelvic pain but occasionally pain in back and legs. Pain is often timed to menses.	Diagnosis suspected during pelvic exam. Vaginal ultrasound is supportive. Laparoscopy is diagnostic.
Retroperitoneal mass, abdominal aortic aneurysm, abscess, hematoma	Pain in back. May be bilateral to spine. May be associated with superimposed neuropathic pain in cases with plexus or proximal nerve involvement.	CT or MRI shows hematoma, aneurysm, eroding vertebral bodies, or abdominal mass.
Urolithiasis	Pain in upper to mid-back laterally that may radiate to groin. No radiation into leg.	Radiographs may show stones. Intravenous pyelography typically shows obstruction of flow. Contrasted abdominal CT usually shows the stone and obstruction.
Diskitis	Pain in lower back exacerbated by movement. Some patients may have radiation of pain to abdomen, hip, or leg.	MRI shows characteristic changes in disk and surrounding tissues.

Table 30.5 Differential Diagnosis of Isolated Leg Pain

Disorder	Clinical Features	Diagnostic Findings
Peroneal neuropathy	Loss of sensation on dorsum of foot. Weakness of foot and toe dorsiflexion.	Slowed nerve conduction velocity across region of entrapment, usually at fibular neck. EMG may show denervation in peroneal-innervated muscles, especially tibialis anterior, without involvement of short head of biceps femoris.
Femoral neuropathy	Pain and sensory loss in anterior thigh, often with weakness of quadriceps and suppression of knee reflex.	NCS can sometimes be performed but may be technically difficult. EMG may show denervation in a distribution limited to femoral nerve.
Piriformis syndrome	Pain from back or buttock down posterior thigh. Pain is exacerbated by sitting or climbing stairs. Stretch of piriformis (flexion and adduction of the hip) worsens pain.	Clinical diagnosis. Pain radiating down leg in a sciatic nerve distribution. Exacerbation of pain by flexion and adduction of hip. EMG and NCS may show proximal sciatic nerve damage.
Meralgia paresthetica (lateral femoral cutaneous nerve dysfunction)	Pain and loss of sensation of lateral femoral cutaneous nerve on lateral aspect of thigh.	Clinical diagnosis. NCS is difficult to perform on this nerve.
Claudication	Pain in thigh and lower leg with exertion. Pain does not occur with lumbar spine extension.	Suspected with exertional leg pain without back pain. Ultrasonography or angiography confirms arterial insufficiency.
Plexopathy	Back and leg pain that has a neuropathic character. Dysesthesias, burning, or electric sensation. Plexitis has no associated back pain.	Suspected when a patient has leg pain in more than one peripheral nerve distribution. MRI of plexus or CT of abdomen can show a structural lesion in some patients.
Radiculopathy	Pain largely in one dermatomal distribution. May be motor and reflex loss. Most patients have back pain, but not all.	Suspected with pain radiating down one leg with or without back pain. Best imaged by MRI or postmyelographic CT.