|Sciatica: Studies of symptoms, genetic factors, and treatment with periradicular infiltration|
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Typically, patients with sciatica due to lumbar disc herniation will present with a sharp, burning, stabbing pain radiating below the knee. The pain is superficial and localized, ”band-like” (Andersson & Deyo 1996, Bogduk 1997a). It is often associated with numbness or tingling (paresthesia) and is aggravated by increased intradiscal pressure or specific movements. There is usually substantial, but incomplete relief with rest. Initially, pain may be felt only in the low back and the buttock(s), but as the disease progresses pain is felt distally along the dermatome. The extent of radiation of pain appears to depend on the severity of the pathologic process affecting the nerve roots (Smyth & Wright 1958). In clinical practice, the physician mostly encounters sciatica caused by irritation of lumbosacral nerve roots L4, L5 or S1. The upper roots (L1-L3) are involved in less than 5% of surgical patients (Andersson & Deyo 1996). Patients with central or lateral lumbar spinal stenosis present typically with leg pain during or after walking (neurogenic claudication). Pain is often bilateral and in contrast to arterial ischemic claudication, neurogenic claudication is more likely to occur on standing alone without ambulation (Deyo et al. 1992).
Pain may be distributed along the whole segment, or confined to certain circumscribed areas. Thus, disease of the L4 nerve root can cause localized pain just below the knee anteriorly and down the shin. L5 nerve root lesion may present with pain in the large toe or over a relatively small area on the anteromedial aspect of the foot and along the fibula. Pain due to S1 nerve root lesions may be felt in the heel or the lateral border of the foot and also in the middle of the calf (Norlen 1944, Agency for Health Care Policy and Research (AHCPR) 1994). There is, however, considerable overlapping between the dermatomes (Nitta et al. 1993). A medical history of current sciatica per se has a high sensitivity for lumbar nerve root compression (AHCPR 1994). The level of disc herniation can be correctly predicted in over 90% of the cases by the pain location alone or supplemented by neurological signs (Kortelainen et al. 1985, Albeck 1996).
The physical examination of sciatic patients should include observation, palpation, determination of the range of motion of the spine, a root tension test and evaluation of the neurological status of the lower limbs. The straight leg raising test stretches the L5 and S1 roots, and this test is regarded positive if leg pain is aggravated when the affected leg (SLR) or the contralateral leg (crossed SLR) is raised (Andersson & Deyo 1996). Root tension tests are sensitive but unspecific as to the location and cause of nerve root irritation. SLR is sensitive, but unspecific, whereas crossed SLR is very specific, but its sensitivity is low (Hakelius & Hindmarsh 1972, Spangfort 1972). L4 root lesions may be accompanied by reduction of the knee jerk whereas impaired ankle reflex is fairly pathognomic for the S1 root (Norlen 1944, Knuttson 1961, Hakelius & Hindmarsh 1972, Spangfort 1972). Reflex testing is less useful in recurrent sciatica, and the lower extremity reflexes often diminish with advancing age (Andersson & Deyo 1996).
The most important muscle strength test involves the extensor hallucis longus, primarily innervated by L5 (Knuttson 1961, Andersson & Deyo 1996). Sensory defects are almost always confined to the periphery of the dermatome. Thus, in L4 root disorders diminished sensation may be present over the medial part of the lower leg, in L5 root lesions over the first three or four toes on the dorsum of the foot, and in S1 root disease along the lateral border and the sole of the foot (Nitta et al. 1993, Bogduk 1997a ). However, the area of sensory loss is a poor predictor of the level of herniation (Blower 1981, Kortelainen et al. 1985). When small nerve fibers were studied using tests for thermal thresholds and the large myelinated fibers by vibrametry, it was found that the adjacent nerve roots are also involved in the pathophysiology of sciatica in patients with lumbar disc herniation (Nygaard & Mellgren 1998).
Clinical examination is recommended to include: 1) testing of dorsiflexion strength of the ankle and the big toe, with weakness suggesting mainly L5 dysfunction; 2) testing of ankle reflexes to evaluate S1 root dysfunction; 3) testing of light touch sensation in the medial (L4), dorsal (L5) and lateral (S1) aspects of the foot; and 4) SLR (Deyo et al. 1992). However, history preselects patients already very likely to have disk herniation, and clinical examination increases the confidence in a positive diagnosis by only two percentage points (Bogduk 1997b); most of the relevant information can be obtained by listening to the patient (Vucetic et al. 1999). The accuracy of neurological tests can, however, be improved by combining the tests (parallel testing) (Andersson & Deyo 1996).
The anatomic level of imaging study findings must correspond to the side and the level of lesion detected via the history, physical examination or other methods. CT (with or without myelography) and MRI should be used only when there exist sciatica and clinically specific detectable nerve root compromise, or history of neurogenic claudication with symptoms severe enough to consider surgical intervention, or clinical findings or other tests suggesting other serious conditions affecting the spine (Agency for Health Care Policy and Research (AHCPR) 1994). Physicians treating sciatic patients should, however, remember that abnormal findings are common among asymptomatic subjects in CT (Wiesel et al. 1984) and MRI (Powell et al. 1986, Paajanen et al. 1989a, Boden et al. 1990, Jensen et al. 1994). There seem not to be clinically important differences between CT, CT-myelography and MRI in terms of their true positive and true negative rates for diagnosing lumbar disc herniation, although all these tests are better than plain myelography (AHCPR 1994). MRI is nowadays regarded as the best imaging mode (Herzog 1996), but in the diagnosis of internal disc ruptures pain provocation is needed. Therefore, a combination of CT and discography is recommended (Vanharanta et al. 1987, Vanharanta et al. 1988a, Vanharanta et al. 1988b, Vanharanta et al. 1989, Moneta et al. 1994). However, discography is an invasive method with possible complications (Guyer & Ohnmeiss 1995), but it can be replaced with the bony vibration test (Yrjämä & Vanharanta 1994). This test, combined with MRI (Yrjämä et al. 1997) or diagnostic ultrasound (Yrjämä et al. 1996), was a sensitive method compared to discography, although the specificity was lower in both studies. Transabdominal ultrasound alone also proved a sensitive screening test for intradiscal abnormalities (Tervonen et al. 1991), but the method depends on the experience of the radiologist performing the analysis.
The diagnostic objectives of electrophysiologic tests are to assess myelopathy (dysfunction of the spinal cord), radiculopathy (dysfunction of a nerve root), neuropathy (dysfunction of a peripheral nerve distal to the nerve root), and myopathy (muscle abnormalities). EMG is used to assess acute and chronic nerve root dysfunction, myelopathy, and myopathy. H-reflex and F-wave response are tests measuring sensory conduction through nerve roots, used mostly to assess S1 radiculopathies and proximal neuropathies, respectively. The results of EMG are, however, unreliable until sciatic pain has persisted for over 3 weeks (Agency for Health Care Policy and Research (AHCPR) 1994) and greater accuracy will be achieved if the EMG results are combined with information from imaging and clinical findings (Spengler et al. 1990).
Pain drawing is independent of language, and correlates with spinal pathology in myelography (Uden & Landin 1987) and in CT/discography (Ohnmeiss et al. 1995). Patients with discogenic pain seem to use more symbols of burning pain and aching pain than patients with nondiscogenic pain (Ohnmeiss et al. 1999b). Pain drawing can also be used in the level diagnosis of lumbar disc pathology (Vuceticn et al. 1995, Ohnmeiss et al. 1999a) and in the qualitative estimation of the hernia type (Vucetic et al. 1995).
The pathophysiological mechanisms of sciatica have recently been the subject of extensive study. On the basis of clinical experiments, it is known that only irritated nerve roots produce pain when compressed (Smyth & Wright 1958, Kuslich et al. 1991). On the other hand, abnormalities are common in asymptomatics (Boden et al. 1990, Jensen et al. 1994). Certain determinants are known to predispose to sciatica and HNP (Heliövaara et al. 1991). The asymptomatic populations in the afore mentioned studies might have been biased with respect to these determinants. However, when symptomatic patients were compared with risk factor-matched controls, disc herniations were common in both groups (Boos et al. 1995). Symptomatic patients could be differentiated only on the basis of neural compromise. Nerve compression and disc extrusion also seem to predict distal leg pain reliably (Beattie et al. 2000).
An association has been observed between the severity of sciatica and the size of lumbar disc herniations on computed tomography adjusted for the size of the spinal canal (Thelander et al. 1994). In addition, impaired walking capacity, pain upon coughing, restriction in SLR and use of analgesics were more common in patients with extruded/sequestered disc herniation than in those with a contained herniation/bulge (Jönsson & Strömqvist 1996). Furthermore, extrusions are uncommon in asymptomatics (Jensen et al. 1994, Weishaupt et al. 1998). The similarity of symptoms in patients with or without disc herniation has been observed (Modic et al. 1995). Although the number of patients in the study was very limited, the results indicate that disc ruptures can be as painful as HNPs.
The amount of inflammatory cells in disc samples does not correlate with the symptoms and signs of sciatica (Grönblad et al. 2000, Rothoerl et al. 1998). The association of nerve root enhancement with sciatic symptoms is far from clear (Toyone et al. 1993, Crisi et al. 1993, Taneichi et al. 1994), whereas SLR restriction seems to correlate with disability (Thelander et al. 1992, Jönsson & Strömqvist 1995).