THE VALUE OF SPECT SCANS IN IDENTIFYING BACK PAIN LIKELY TO BENEFIT FROM FACET JOINT INJECTION

Transcription

1 British Journal of Rheumatology 1996;35: THE VALUE OF SPECT SCANS IN IDENTIFYING BACK PAIN LIKELY TO BENEFIT FROM FACET JOINT INJECTION A. L. DOLAN, P. J. RYAN, N. K. ARDEN, R. STRATTON, J. R. WEDLEY,* W. HAMANN,* I. FOGELMANt and T. GIBSON Clinical Rheumatology Unit, *Pain Relief Unit and ^Nuclear Medicine Department, Guy's Hospital, London SUMMARY Lumbar facet disease is sometimes implicated in low back pain. Identification is difficult and this may account for a variable response. Single photon emission computerized tomography (SPECT) is a scanning technique which enables localization of facet joint pathology. We determined whether recognition of facet disease by this method improved the response to corticosteroid injection treatment. Fifty-eight patients with low back pain and displaying accepted clinical criteria for facet joint disease were evaluated by SPECT. Twenty-two had facetal uptake of isotope. These and the tender facet joints of 36 scan-negative patients were injected with 40 mg methylprednisolone and 1 ml 1% lignocaine under X-ray control. Pain was assessed by a blind observer using the McGill questionnaire (MGQ), Present Pain Intensity score (PPI) and a Visual Analogue Scale (VAS). VAS, PPI and MGQ were reduced in the scan-positive patients at 1 month (P = 0.05, P = , P = 0.005) and MGQ at 3 months (P = 0.01), whilst scan-negative patients were unchanged. The percentage of scan-positive patients who reported improvement was 95% at 1 month and 79% at 3 months, significantly greater than the control group (P = , P =» 0.01). Within 6 months, pain improvement in the SPECT-positive group was no longer statistically significant. Tenderness did not correlate with increased uptake on SPECT scan. Osteoarthritis of the facets was more common in the SPECT-positive patients (P < 0.001), but did not correspond with sites of increased uptake on SPECT scan. These results suggest that SPECT can enhance the identification of back pain sufferers likely to obtain short-term benefit from facet joint injection. KEY WORDS: Imaging, Bone scan, Spinal pain, Treatment. IT is thought that low back pain deriving from facet joints is characterized by local tenderness and pain on spinal extension and exercise [1-3]. These features have been endorsed by observing pain distribution after stimulating the facets [4,5]. However, there are reservations about such crude clinical criteria. These doubts could account for the inconclusive results of previous studies of facet joint injection treatment [6-8]. Identification of facet pathology by X-ray is unhelpful [9] and CT scans, although more reliable at detecting structural changes, are unable to distinguish relevant from incidental abnormalities [2, 10]. Bone scans are sensitive at identifying sites of skeletal and related tissue pathology, but their application to back pain has been limited by the difficulty of determining the precise anatomical location of activity. Single photon emission computerized tomography (SPECT) is an extension of this technique and overcomes the problem by rotating the gamma camera to give a topographical image. This improves sensitivity by producing better spatial information and multiplanar views [11, 12]. SPECT has enabled activity from the posterior elements to be visualized separately from that arising in vertebral bodies and, in particular, has enabled activity arising from the facet joints to be detected [13]. A recent study has suggested that many patients with chronic low back pain have foci of increased activity Submitted 25 January 1996; revised version accepted 29 May Correspondence to: T. Gibson, Clinical Rheumatology Unit, Shepherds House, Guy's Hospital, London SE1 9RT. arising from one or more facet joints, as demonstrated by SPECT [14]. These foci are often associated with facetal disease on CT scans and may represent the site of origin of pain [9, 15]. Thus, bone scintigraphy with SPECT may be a valuable tool for the recognition of pain arising from facetal disease. This is supported by studies in which most of those with increased SPECT uptake at facet joints responded to injection of local anaesthetic [16, 17]. This study assessed the value of injecting facet joints showing increased SPECT activity in patients with clinical features thought to indicate facet disease (Fig. 1). Our hypotheses were that (i) abnormal SPECT uptake implies pathology and thus the origin of pain and (ii) the response to facet injections could be improved by more precise identification of suitable patients for treatment. METHOD Patients were recruited from the rheumatology departments of Guy's, Lewisham and the Brook Hospitals. All had low back pain of at least 3 months duration and fulfilled the criteria for facet joint pain, namely, more pain on spinal extension than flexion, pain relieved by rest and worsened by sitting or standing and not made worse by coughing or sneezing. Any patients with signs of nerve root compression, previous spinal surgery or general ill health were excluded. Patients gave written consent for the study and were evaluated with a clinical history and general examination. Haemoglobin, WBC, ESR and bone biochemistry were performed to exclude any inflammatory or metabolic disorder. Sites of tenderness British Society for Rheumatology

2 1270 BRITISH JOURNAL OF RHEUMATOLOGY VOL. 35 NO. 12 were recorded. Spinal flexion was measured by the modified Schober index [18] and spinal extension as described by Moll and Wright [19]. Patients completed a modified McGill Pain Questionnaire (MPQ) [20], Present Pain Intensity score (PPI) [20] and a Visual Analogue Score for Pain (VAS). Three assessments of pain were utilized because none is capable of encompassing all elements of the pain experience. The MPQ measures the quality of pain, whereas PPI and VAS are indications of its intensity. Concomitant analgesic requirement was noted, but no other treatment was permitted. X-rays of the lumbar spine including oblique views were obtained. AU patients underwent planar bone scintigraphy followed by SPECT scanning of the lumbar spine. (a) Bone scintigraphy was undertaken after i.v. injection of 750 MBq Tc-99m MDP. Planar imaging of the spine and pelvis was performed after 3 h, followed by SPECT of the lumbar spine using a rotating gamma camera equipped with a high-resolution collimator. An elliptical 360 orbit was used with 64 projections and 20 s per projection. Acquisition was into a 128 x 128 matrix. X-rays were examined by an independent observer who was blind to the clinical and scan details. The presence or absence of facetal joint OA was noted. Planar and SPECT images were assessed by a nuclear medicine physician, independent of the clinical or radiographic data. Only scans which were unequivocally abnormal were counted as positive. Inter- and POST (b) FIG. 1. (a) Planar bone scan of lumbar spine. No anatomically precise abnormality was seen, (b) Single photon emission tomography (SPECT) in the same patient showing increased uptake at both L4/5 facet joints.

3 DOLAN ET AL.: SPECT SCANS IN BACK PAIN 1271 TABLE I Details of SPECT-positive and SPECT-negative patients on entry to the study. Figures represent the median (range) or mean (S.E.) Gender Age(yr) Duration (months) PPI score McGill pain VAS (mm) Extension (cm) Flexion (cm) SPECT positive 7 M 12 F 54(34-66) 3 (3-30) 2.65 (0.28) 28.3 (2.8) 60.1 (4.7) 5.37 (0.64) 5.56 (0.29) SPECT negative 15 M 20 F 41 (18-78) 3 (3-27) 2.82 (0.21) 30.6 (1.3) 58.1 (3.4) 4.98 (0.49) 5.89 (0.29) intra-observer error were not assessed, and reliance was placed on the judgement of the nuclear medicine physician, as is conventional with other imaging techniques. Patients with increased SPECT uptake at the lumbar spine facet joints were injected at these sites with 0.5 ml of 1 % lignocaine and 40 mg of methylprednisolone, by an experienced anaesthetist underfluoroscopic control. A 22 gauge spinal needle was placed in the joint space during biplanar X-ray screening following local infiltration of skin and s.c. tissues with 0.5% lignocaine. Where there was resistance to injection, the needle was repositioned. If resistance persisted, the needle was withdrawn to avoid rupture of the joint capsule. Where the joint space could not be clearly seen, the injection was placed adjacent to the joint. Patients with the same clinical pattern, but without uptake at the facet joints on SPECT, received a similar injection into the facet joints approximating to sites of maximal tenderness using the same fluoroscopic control, and the same size of needle and dose of corticosteroid. Where in any one patient there was more than one SPECT-positive site or area of tenderness, all relevant facets were injected. Clinical assessments were repeated at 1, 3 and 6 months following injection. Results were analysed using Mann-Whitney and x 2 tests. RESULTS Fifty-eight patients were enrolled in the study; 22 had positive SPECT scans and 36 were negative. Five patients had two active facets and one had three active sites. Four patients were excluded from analysis: two because of technically unsuccessful injection (both SPECT positive) and two because after admission to the study they developed sciatica and CT evidence of disc protrusion with root compression (one SPECT positive and one negative). No follow-up measurements were performed on these cases. The sex distribution and disease duration were similar in the two groups, but those who were SPECT positive were older (Table I). Prior to treatment, there was no difference in any of the parameters of pain or spinal mobility. There was no difference between groups in number of injections or total amount of steroid received; the 19 patients with SPECT-positive scans were injected at 25 sites, the 35 SPECT-negative patients were injected at 44 sites (average 1.3 sites for both groups). Patients with positive SPECT scans showed significant improvement in pain (VAS) at 1 month compared with SPECT-negative patients (P < 0.05), and with pre-treatment values at 1 and 3 months (P = 0.002, P = 0.05). Pain (VAS) did not change significantly in the SPECT-negative group (Table II). The McGill pain score in the SPECT-positive group was significantly better than that in the SPECT-negative group at 1 and 3 months (P = 0.005, P = 0.01) (Table II). Present pain intensity score improved at 1 month in the SPECT-positive group (P = ). Spinal extension and flexion exhibited no significant change in either group (Table II). At the end of the study, eight (42%) SPECT-positive and five (14%) SPECT-negative patients had stopped analgesics (X 2 = 5.2; P = 0.02). Of those with positive scans, 94% reported improvement at 1 month, but only 47% of scan-negative patients did so (P = ). At 3 months, 79% of those with positive scans reported improvement, compared with 42% of scan-negative cases. The number of patients who reported improvement was significantly greater than the control group at 1 (P < ) and 3 months (P < 0.01). The statistically significant improvement of pain evident after 1 and 3 months in SPECT-positive patients had disappeared by 6 months, although mean results were still lower than pre-treatment values. Only 3/22 patients with positive scans had a site of tenderness corresponding to the location of increased uptake on SPECT. Suitable oblique spinal X-rays were available on 46 patients and 9/19 (47%) of those with positive SPECT scans had OA changes at the facet joints, compared to TABLE II Effect of treatment on scores of pain and spinal movement in SPECT-positive and SPECT-negative patients. Results are expressed as mean (±s.d.) PPI VAS McGill Extension Flexion (0.28) 2.82 (0.21) 60.1 (4.7) 58.1 (3.4) 28.3 (2.8) 30.6 (1.3) 5.37 (0.64) 4.98 (0.49) 5.56 (0.29) 5.89 (0.29) Time (months) (OAT)* 2.15 (0.25) 3.52 (0.95) 2.55 (0.19) 33 (5.9)* 53 (4.3) 22.1 (1.9)'* (1.6) 5.9 (0.65) 6.11 (0.68) 5.78 (0.32) 6.03 (0.29) *P < 0.05; **P < 0.005; */> < (6.2) 51.7 (4.4) 23.4 (2.7)" 30.2 (1.9) 5.9 (0.58) 5.5 (0.57) 5.44 (0.28) 5.74 (0.36) (0.33) 2.76 (0.21) 43.8 (5.8) 55.9 (3.9) 27.2 (2.4) 29.4 (1.6) 6.3.(0.58) 6.14(0.49) 5.56 (0.24) 6.11 (0.35)

4 1272 BRITISH JOURNAL OF RHEUMATOLOGY VOL. 35 NO. 12 5/27 (18%) of the SPECT-negative group (P < 0.001). However, only 6/22 (20%) SPECT-positive facets corresponded with X-ray evidence of OA at these sites. DISCUSSION In this study, patients who were injected at sites of increased uptake on SPECT scans showed significant improvement at 1 and 3 months for McGill pain score. Of those with positive SPECT scans, 94% reported improvement at 1 month. There was no significant improvement in patients with negative scans. Mooney and Robertson [3] first reported intra-facet steroid injection and noted long-term improvement in 52%. Facet joint injection has been used for both diagnosis and treatment, and long-term improvement reported in 20-30% [21, 22]. However, Raymond and Dumas [6] showed that only 16% of patients had short-term improvement when contrast and local anaesthetic were confined to the capsule, suggesting that previous benefits may have arisen by treating a wider extra-articular area. Controlled studies using corticosteroid and local anaesthetic injection showed no benefit over saline [7, 8]. Our study suggests that SPECT scanning improves patient selection and localization of the relevant facet joint. The clinical features of facet pain were originally defined after the injection of saline into facet joints and the recognition of similar distributions of pain in a clinical setting [1, 4, 5]. With the possible exception of disc pathology, symptoms and signs of low back pain are often non-specific. We found increased uptake on SPECT in only 37% of the total who satisfied the criteria for facet disease. Since the response to injection was significantly enhanced when directed at a focus of increased SPECT activity, it would seem that these foci do locate facet disease. In our practice, local anaesthetic and steroid injection are often used to screen patients before facet denervation [23]. The study has shown the benefit of local anaesthetic and steroid injection for periods of up to 6 months, although relapses increased with time. Those experiencing transient improvement could benefit from subsequent denervation. Sites of tenderness had little relationship to increased uptake on SPECT scan. Thus, reliance on clinical determination of facet joints suitable for injection is questionable. Some practitioners inject multiple levels in order to overcome the imprecision of clinical assessment, but this is time consuming. Facet joints are innervated from branches to the posterior primary ramus at the corresponding level and from the nerve root above, which may account for the inaccurate localization of pain. There was no association between increased uptake on SPECT scanning and X-ray change at specific facet joints, although positive scans were more likely to occur in those with facet OA at other sites. The SPECT lesion could be an early stage of OA not visible on X-ray and possibly more steroid responsive. Alternatively, the lesion at the facet joints may not be degenerative in all cases. Bone scan activity may indicate hyperaemia, with increased uptake reflecting an area of inflammation secondary to a mechanical trigger point. Einstein and Parry [2] have suggested that facetal pain is the result of a concise arthritic syndrome. They identified a process of cartilage necrosis, ulceration and subchondral cysts without osteophytes. This resembled the changes seen in chondromalacia patellae. SPECT scanning is simple and cheap to perform with modern equipment. It takes ~ 25 min for a single-headed camera and 15 min for a dual-headed camera. This study shows that scanning in low back pain results in improved localization of metabolically active facet joints and a better clinical outcome after local steroid injection. Since the clinical criteria of facet disease are so poor, we advocate SPECT scanning in all patients with non-discogenic chronic back pain. Amongst these may be patients who would derive benefit from facet injection. ACKNOWLEDGEMENT We are grateful to the Arthritis and Rheumatism Council for supporting this study. REFERENCES 1. Ghormley RK. Lower back pain with special reference to the articular facets, with presentation of an operative procedure. / Am Med Assoc 1933;101: Eisenstein SM, Parry CR. The lumbar facet arthrosis syndrome. J Bone Joint Surg 1987;69B: Mooney V, Robertson J. The facet syndrome. Clin Orthop 1976;115: Hirsh C, Ingelmark BO, Miller M. 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