|Sciatica: Studies of symptoms, genetic factors, and treatment with periradicular infiltration|
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There is a high remission rate in acute non-specific LBP, with approximately 90 % resolving within 6 weeks (Frymoyer 1988, Carey et al. 1995). The recovery rate from sciatica is not as rapid as for patients with LBP (Andersson et al. 1983). In a recent study, most sciatic symptoms and signs had cleared within the first 3 months (Balague et al. 1999). At the 1-year follow-up, one third of the patients had recovered fully, and one third had undergone surgery. In another study, only 11.4% of conservatively treated sciatic patients reported that the predominant pain had completely disappeared at the 1-year follow-up assessment (Atlas et al. 1996).
However, the long-term prognosis of sciatica and lumbar herniations seems to be good (Hakelius 1970, Weber 1983, Saal et al. 1990a, Weber et al. 1993). Large disc herniations will resorb without treatment more quickly than smaller herniations (Maigne et al. 1992, Ito et al. 1996, Ahn et al. 2000). Return to work is usually governed by extraspinal factors, being closely linked in industrialized countries to the legal framework of social insurance (Waddell et al. 1986). Female sex, longer duration of symptoms, litigation or compensation pending, poor psychosocial circumstances and comorbidities have been shown to be associated with poor outcomes (Hurme & Alaranta 1987, Junge et al. 1995, Carragee & Kim 1997).
Recommendations about conservative (or surgical) treatment of sciatica are handicapped by the limited number of randomized controlled trials (RCT). A recent systematic review found only 19 RCTs, of which 8 met the three major requirements (comparability of groups, observer blinding, and intention-to-treat analysis) (Vroomen et al. 2000). In the 1980s, the treatment of sciatica consisted of 2 weeks bed rest, and thereafter gradual mobilization combined with anti-inflammatory drugs (NSAIDs) (Bell & Rothman 1984). Nowadays, bed rest for sciatica is no more recommended (Vroomen et al. 1999). On the basis of this systematic review, no significant effect was demonstrated for NSAIDs, traction, or intramuscular steroids; only epidural steroids were possibly shown to have some benefit (Vroomen et al. 2000). In the following sections, epidural steroids and periradicular infiltration are discussed further.
Epidural injection of medication allows a concentrated amount of the treatment agents to be deposited and retained, exposing the nerve roots to the medication for a prolonged period of time. When a combination of epidural steroid and anaesthetic was compared with local anaesthetic at a tender spot over the sacrum, epidural steroid was superior at 3 months, but not at the 1, 6, or 12-month follow-up assessments (Mathews et al. 1987). A combination of epidural steroid and anaesthetic was found to give better short-term (3–4 weeks) leg pain relief than epidural saline (two injections 2 weeks apart) (Bush & Hillier 1991), than epidural anaesthetic (bupivacaine) (Breivik et al. 1976), and than interspinous injections (Dilke et al. 1973, Ridley et al.1988). No long-term effect of this combination has been observed (Dilke et al. 1973, Snoek et al. 1977, Klenerman et al. 1984, Bush & Hillier 1991), although the return to work rate was better in the steroid group in one study (Dilke et al. 1973). In some studies, not even short-term relief was found (Snoek et al. 1977, Klenerman et al. 1984, Cuckler et al. 1985). In a recent study, up to three epidural injections of methylprednisolone acetate were compared with saline among patients with sciatica due to HNP (Carette et al. 1997). In the steroid group, significant improvements were found in finger-to-floor distance and sensory deficits at 3 weeks, and leg pain at 6 weeks. At three months, there were no significant differences between the groups and the cumulative probability of back surgery was similar (around 25 %). As a conclusion the authors stated that despite the short-term improvement in leg pain and sensory deficits, epidural steroid injection offers no significant functional benefit, nor does it reduce the need for surgery (Carette et al. 1997). Two meta-analyses of epidural corticosteroids have been conducted. One found no, or at most a short-term effect of epidural steroids in LBP and sciatica (Koes et al. 1995), whereas the other found epidural steroid effective in radicular pain in both the short- and long-term (Watts & Silagy 1995). Epidural corticosteroid injections can be recommended as additional therapy, especially in the acute phase of the conservative management of sciatica (Buchner et al. 2000, Vroomen et al. 2000).
Periradicular (transforamimal) infiltration was developed in the late 1960s by Ian Macnab (Macnab 1971). It has since been used for diagnostic purposes – mostly when surgery is considered (Krempen & Smith 1974, Wilppula & Jussila 1977, Herron 1989, Stanley et al. 1990). In the procedure, the pharmaceutical agents are injected between the nerve root and the epiradicular sheath, depicting the nerve root in tubular fashion (Hasue & Kikuchi 1997), which permits precise application of steroids into the vicinity of the irritated nerve root resulting in a massive concentration of the agent at the site (Derby et al. 1992, Weinstein et al. 1995). An accuracy of 85% to 94% in identifying a single symptomatic root, sensitivity of 100%, and positive predictive value of 93% to 95% have been presented for periradicular infiltration (Haueisen et al. 1985, Dooley et al. 1988, van Akkerveeken 1996, Hasue & Kikuchi 1997). Indications for periradicular infiltration include radicular pain and/or intermittent claudication without neurologic findings, atypical leg pain, multiple nerve root signs, radicular pain and/or intermittent claudication associated with other types of pain, multilevel abnormalities on imaging studies, discrepancy between imaging studies and clinical findings, nerve root and/or spine anomalies, failed back syndrome, and intra- and extraforaminal lesions (Hasue & Kikuchi 1997). The mechanism of periradicular infiltration may be blocking of afferent impulses from the periphery (Hasue & Kikuchi 1997), or increased intraradicular blood flow (similar to after symphathetic ganglion block) (Yabuki & Kikuchi 1995).
Patients with lumbar spinal stenosis due to spondylosis or degenerative spondylolisthesis had more therapeutic benefit than those with disc herniation and spondylolytic spondylolisthesis (Kikuchi et al. 1984, Hasue & Kikuchi 1997). Recent uncontrolled studies confirm these observations of a therapeutic effect (Weiner & Fraser 1997, Lutz et al. 1998). In HNP induced radiculopathy, there was a 75 % long-term recovery after on average of 1.8 transforaminal injections per patient of betamethasone acetate combined with xylocaine. The outcome was better, with symptom duration of less than 36 weeks (Lutz et al. 1998). Nerve root injection is also effective in sciatica due to lateral disc herniations, which are difficult to treat by other therapeutic means (Weiner & Fraser 1997). For postoperative radicular pain, however, the technique seems not to have therapeutic effect, and CT-guided injection seems to be superior to fluoroscope-assisted for both its visualization and a longer-lasting effect (Lutze et al. 1997). An MRI-guided procedure can be recommended for S1-infiltrations (Ojala et al. 2000).
The outcome of patients operated for disc herniation has been reported to be superior to that of conservatively treated patients (Nykvist et al. 1989, Atlas et al. 1996), but for mild symptoms the benefits of surgical and conservative treatments are similar (Atlas et al. 1996). Only one RCT compared standard discectomy with conservative therapy (Weber 1983). At the 1-year follow-up there were significantly more patients with good or fair results in the surgery group (90% vs. 61% in non-surgery group), but at the 4- and 10-year follow-ups the results were similar in both groups. During the first year, 26% of the nonsurgery group demanded discectomy because of unrelieved sciatic pain (Weber 1983).
It has been estimated that 5 to 20 % of patients with symptomatic HNP require surgery (Heliövaara et al. 1987, Deyo et al. 1990, Frymoyer 1992), but even higher figures have been obtained (Balague et al. 1999). According to the Mini-Finland survey, 32 % of sciatic patients had been in hospital and 21% operated on for a low-back condition (Heliövaara et al. 1989). In 1995, the overall rate of lumbar disc surgery in Finland was nearly 78 per 100 000 (Keskimäki et al. 2000). The clinician should consider referral to a specialist for disc herniation surgery when all of the following conditions are met: 1) sciatica is both severe and disabling, 2) symptoms of sciatica persist without improvement or with progression, and 3) there is clinical evidence of nerve root compromise (Agency for Health Care Policy and Research (AHCPR) 1994).