COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF SACROILIITIS

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1 1479 COMPUTED TOMOGRPHY IN THE DIGNOSIS OF SCROILIITIS FRNKLIN KOZIN, GUILLERMO F. CRRER, LWRENCE M. RYN, DENIS FOLEY, and THOMS LWSON Computed tomography (CT) and conventional radiography of the sacroiliac joint were compared in 43 patients. CT appeared to be far more sensitive and equally specific in the recognition of sacroiliitis. In a number of patients with sacroiliitis diagnosed by both techniques, CT demonstrated abnormalities that were not demonstrated by conventional radiographs. Of those patients with clinical evidence of sacroiliitis and HL- 27 positivity, 50% had negative or equivocal radiographs compared to 19% who had negative computed tomographic images for sacroiliitis. subsequent studies have shown that this technique is not specific for sacroiliitis (5-9). We have investigated the value of high-resolution computed tomography (CT) for the detection of sacroiliitis. This technique should have the same or better specificity as conventional radiography because identical morphologic criteria are used for analysis and images are more distinct. Moreover, CT should be more sensitive than conventional radiography because the confusing effects of overlying soft tissue or bony structures may be minimized. Radiographic demonstration of sacroiliitis is essential for the early diagnosis of ankylosing spondylitis (1,2) and related spondylarthropathies. Conventional radiographic methods are relatively insensitive because of the curved, oblique orientation of the sacroiliac joint and because of overlying bony and soft tissue structures. Recently, scintigraphic methods were introduced for early demonstration of sacroiliitis,.and the results were encouraging (3,4). Unfortunately, From the Departments of Medicine and Radiology, The Medical College of Wisconsin, and Milwaukee County Medical Center, Milwaukee, Wisconsin. Supported in part by grants from the NIH (M ) and the rthritis Foundation. Franklin Kozin, MD: ssociate Professor of Medicine, Division of Rheumatology ; Guillermo F. Camera, MD: ssistant Professor, Department of Radiology; Lawrence M. Ryan, MD: ssistant Professor of Medicine, Division of Rheumatology; Denis Foley, DDR: ssistant Professor, Department of Radiology; Thornas L. Lawson, MD: ssociate Professor, Department of Radiology. ddress reprint requests to Franklin Kozin, MD, scripps clinic and Research Foundation, Immunopathology D ~ ~ ~. N., Torrey Pines, La Jolla, C Submitted for publication J"]Y 1, 1980; accepted in revised form May 29, ~i~~~~ 1. computed radiograph (Scout view), performed at the time of CT examination, demonstrates the lumbosacral junction in lateral projection. The correct gantry level (black line) and gantry angle (white line) necessary to produce transaxial images of the sacroiliac joint are obtained from this preliminary study, using a computer program. Consecutive CT images are taken in the plane Of the sacrum. rthritis and Rheumatism, Vol. 24, No. 12 (December 1981)

2 1480 KOZIN ET L C Figure 2., Diagram of a section through the midportion of the sacroiliac joint in the straight transaxial plane. The dorsal (D) compartment of the joint is ligamentous, with an irregular cortical surface due to insertional pits (open arrows) for the sacroiliac ligaments. The synovial compartment is ventral (V), and has smooth, parallel surfaces (arrows). S = sacrum; I =: ilium., Diagram of a section through the ligamentous portion of the sacroiliac joint, such as those obtained at a cephalad-dorsal level in the angled transaxial plane. y :? s orientation, sections entirely through the ligamentous or synovial compartment of the sacroiliac joint can be obtained. Insertional pits (open arrows) help identify the ligamentous compaament. C. The caudal-ventral sections through the sacroiliac joint in the angled, transaxial plane show the synovial compartment to advantage. The opposing cortical surfaces are smooth and parallel.

COMPUTED TOMOGRPHY IN SCROILIITIS DIGNOSIS 148 1 Table 1. tients Demographic characteristics and diseases of the 43 pa- Characteristics and diseases* Demography ge 33.3 2 2.

3 COMPUTED TOMOGRPHY IN SCROILIITIS DIGNOSIS Table 1. tients Demographic characteristics and diseases of the 43 pa- Characteristics and diseases* Demography ge years Sex distribution 16 F, 27 M Disease duration months Duration of LP (n = 29)t months HL-27 positive 27 (66%)$ Disease nkylosing spondylitis Reiter s syndrome Psoriatic arthritis Inflammatory bowel disease Juvenile rheumatoid arthritis Nonspecific sacroiliitis symmetric polyarthritis LP, other etiologies Other Total Number of patients * Mean 2 SEM, n = 43 unless stated otherwise. t LP = low back pain. t Tissue typing performed in 41/43 patients. 0 Includes rheumatoid arthritis in I, tophaceous gout with probable sacroiliac joint involvement in I, and unknown in 2 patients. Table 2. Correlation between HL-?7 and clinical sacroiliitis Clinical sacroiliitis HL-27 Present bsent Total Positive Negative 4* Total * These patients include a 35-year-old white man who has a family history of Reiter s syndrome; a 23-year-old white woman who has asymmetric polyarthritis and sacroiliitis according to radiologic findings; a 50-year-old white woman who has tophaceous gout and radiologic abnormality of the sacroiliac joint; and a 30-year-old white man who has psoriatic arthritis and sacroiliitis according to radiologic findings. Table 3. comparison of the,radiographic and CT findings Radiographic findings CT image results Positive Equivocal Negative Positive Negative Total PTIENTS ND METHODS Patients. Forty-three consecutive patients who had chronic low back pain or clinical findings indicative of sacroiliitis or a spondylitic syndrome were studied. Patients were classified according to their clinical findings, as previously defined ( 10). Sacroiliitis was diagnosed in patients who had a typical history of inflammatory chronic low back pain (1 1) associated with tenderness of the sacroiliac joints or limitation of lumbar motion. HL tissue typing was performed in all but 2 patients. Radiologic studies. Computed tomography (CT) of the sacroiliac joint was performed by the General Electric CT/T 8800 scanner, as previously described (12). The correct anatomic level and gantry angle for scanning were estab- Figure 3., Conventional radiograph of the sacroiliac joint shows bilateral joint space irregularity, erosions, iliac sclerosis, and indistinct cortical margins. joint space is apparent bilaterally., CT images through the articular portion of the sacroiliac joint show severe joint space narrowing, marginal irregularity, and advanced iliac and sacral sclerosis on the right. The left sacroiliac joint is completely obliterated with bony ankylosis of the entire joint; this finding was unsuspected from the conventional radiograph. n

Schematic views of the sacroiliac joint are shown in Figure 2-C and illustrate the crosssectional anatomy of this area as it appears on CT images.

4 1482 KOZIN ET L lished by computed radiography before CT (Figure 1). Six to 8 tomographic images were obtained for analysis. In a preliminary study, the normal CT image of the sacroiliac joint was defined (12), and these results were used for comparison during this series. Schematic views of the sacroiliac joint are shown in Figure 2-C and illustrate the crosssectional anatomy of this area as it appears on CT images. Conventional radiographs included posteroanterior (P) view of the pelvis, P view of the sacroiliac joints with a 30" caudal tube angle, and oblique views of the sacroiliac joint. Three radiologists (GFC,DF,TL), who were experienced in CT and who had no knowledge of the clinical or radiographic findings, examined the CT images. radiologist and two rheumatologists (GFC,FK,LMR), who had no knowledge of the clinical or CT findings, read the conven- tional radiographs. oth the CT images and radiographs were interpreted according to the following criteria: sacroiliitis positive if bony ankylosis, sclerosis on both sides of the joint, cortical erosions, or irregular joint space narrowing was present; sacroiliitis equivocal if sclerosis was present only on the iliac side of the joint (because it was difficult to completely exclude coexistent sacral sclerosis); and sacroiliitis negative if only isolated iliac sclerosis was present on CT images. RESULTS Patients. The demographic characteristics and diseases of the 43 patients are shown in Table 1. These diagnoses were based upon clinical findings only. C Figure 4., Conventional radiograph of the sacroiliac joint shows no evidence of sacroiliitis. The cortical margins are well preserved. Mild inferior iliac sclerosis is present., CT image at a more dorsal (posterior-superior) level shows irregular joint space narrowing in the synovial portion of both sacroiliac joints. There is marginal irregularity and moderate iliac sclerosis. C, CT image at a more ventral (anterior-inferior) level shows advanced erosions throughout the synovial portion of the sacroiliac joints (arrow). There is extensive sclerosis on both sides of the joints (arrowhead).

COMPUTED TOMOGRPHY IN SCROILIITIS DIGNOSIS 1483 Figure 5., Conventional radiograph shows extensive sclerosis and a large erosion at the inferior portion of the left sacroiliac joint.

5 COMPUTED TOMOGRPHY IN SCROILIITIS DIGNOSIS 1483 Figure 5., Conventional radiograph shows extensive sclerosis and a large erosion at the inferior portion of the left sacroiliac joint. The right sacroiliac joint appears normal with intact joint margins and no sclerosis or ankylosis., CT images confirm the change on the left, but demonstrate more extensive joint space narrowing than suggested by the radiograph. The right sacroiliac joint is irregular and narrowed as well (arrow) and shows considerable subcortical osteoporosis; these changes were not evidenced radiographically. highly significant correlation was present between HL-27 positivity and a clinical diagnosis of sacroiliitis, P < (chi-square analysis), as shown in Table 2. Radiologic studies. Results of the radiographic and CT findings are compared in Table 3. Fifteen patients had definite evidence of sacroiliitis by conventional radiography; all of these had definite sacroiliitis by CT as well. In a number of cases, CT demonstrated more extensive erosions and/or areas of ankylosis or sclerosis that were not evident radiographically (Figure 3). Conventional radiographs of 28 patients resulted in negative or equivocal findings. Thirty-two percent of these patients (9 of 28) were sacroiliitis-positive by CT (Figures 4-6). ecause the interpretations of the CT images and radiographs were based upon identical criteria, it is unlikely that the additional cases of sacroiliitis found by CT represented false positives. To examine this possibility more carefully, we correlated the CT and radiograph results with the clinical findings and HL types of our patients (Table 4). Sacroiliitis was more prevalent in the HL-27-positive patients according to both CT and conventional radiography, but these differences were not statistically significant. In contrast, CT and radiographic demonstration of sacroiliitis was highly correlated with the clinical finding of sacroiliitis. Sixteen patients who were HL-27 positive and had sacroiliitis according to our clinical criteria ( definite spondylarthritis ) were compared to 10 patients who lacked both these findings ( nonspondylarthritis ). The results are shown in Table 4. CT improved our ability to recognize sacroiliitis in the definite spondylarthritis patients. The number of nonspondylarthritis patients diagnosed as sacroiliitis-positive increased from 10% to 30% by use of CT. However, it is unlikely that these represent false positives, because 1 patient s sacroiliitis was diagnosed by both CT and radiography and another had a clinical syndrome consistent with Reiter s disease (see Table 4). DISCUSSION The present study suggests that high-resolution computed tomography (CT) of the sacroiliac joints is more sensitive than conventional radiographic methods. Sacroiliitis was found in 56% of our patients by CT, compared to 35% by radiography. CT resulted in abnormal findings in 9 patients (21% of the entire group) whose conventional radiographs had resulted in normal (6 patients) or equivocal (3 patients) findings. Five other patients for whom the radiographs demonstrated equivocal results for sacroiliitis had normal findings by CT. Even in those cases in which both CT and conventional radiographs resulted in abnormal findings, often more extensive disease was revealed by

- _- 1484 KOZIN ET L Figure 6., Conventional radiographs were interpreted as equivocal because of mild iliac sclerosis on the right.

6 - _ KOZIN ET L Figure 6., Conventional radiographs were interpreted as equivocal because of mild iliac sclerosis on the right. The joint spaces are well preserved, and there are no definite erosions., CT images through the sacroiliac joints show almost complete obliteration of the articular space bilaterally. There is marked sclerosis and irregularity of both sides of the joint on the left (arrow), indicating sacroiliitis. CT than by radiography. These results are not surprising because CT should be ideally suited to imaging the curved, oblique sacroiliac joint. Interference from soft tissue and bony structures can be eliminated by CT, and the plane of the computer tomographic image is oriented to the transaxial plane of the joint by CT (12). The sensitivity and specificity of CT and radiography was compared by classifying two groups of patients according to clinical and serologic criteria: a spondylitic group who were HL-27 positive and Table 4. Correlation of clinical findings and HL-27 with CT and radiographic demonstration of sacroiliitis ~ Number % positive Clinical finding of patients Radiograph* CT image - ~ _. 27 positive negative Sacroiliitis presentt 20 5s 80 Sacroiliitis absent and sacroiliitis + 27 or sacroiliitis so and sacroiliitis $ * Equivocal radiographs were considered negative. - One of these 3 patients had abnormal sacroiliacjoints according t Sacroiliitis was determined clinically. t. to both radiographic and CT. second is a 23-year-old woman with asymmetric polyarthritis and an equivocal conventional radiograph. The third patient is a 29-year-old man with a 6-week history of asymmetric polyarthritis, nongonococcal urethritis, and circinate balanitis. had clinical evidence of sacroiliitis, and a nonspondylitic group who were HL-27 negative and had no clinical evidence of sacroiliitis. The sensitivity, defined as the frequency of sacroiliitis in the spondylitic group (positive test in the true positive population), of CT (81%) was considerably greater than conventional radiography (50%) (Table 4). It was more difficult to assess relative specificities, defined as the frequency of negative sacroiliac joint studies in the nonspondylitic group (negative tests in the true negative population). Ten patients were included in the nonspondylitic group; however, 1 patient had abnormal sacroiliac joints by both CT and radiography, and 2 others had clinical characteristics consistent with a spondylarthritis (Table 4). ased upon these clinical correlations, we believe the specificity of conventional radiography and CT are comparable. These findings are important because the diagnosis of definite sacroiliitis depends on its radiographic demonstration. Conventional radiography failed to detect sacroiliitis in 50% of the 16 patients who had definite spondylitis as defined clinically and serologically. This was reduced to 19% by the use of computerized tomography. These studies establish the value of CT in the diagnosis of sacroiliitis. CT has significant advantages over conventional radiography, including high sensitivity and reduced gonadal radiation (12). CT is preferable to scintigraphy because of its greater specificity.

7 COMPUTED TOMOGRPHY IN SCROILIITIS DIGNOSIS 1485 Nevertheless, CT cannot be applied to routine evaluation of the sacroiliac joint at this time because of its limited availability and cost. We suggest that it be used for patients who have radiographs with normal or equivocal results and in whom a spondylarthritis is highly suspect REFERENCES Kellgren JH, Jefferey MR, all J, editors: The Epidemiology of Chronic Rheumatism. Vol 1. Oxford, lackwell, 1%3, p 326 ennett PH, Woods, PHN: Population Studies of the Rheumatic Diseases. msterdam, Excerpta Medica, 1968, p 456 Russell S, Lentle C, Percy JS: Investigation of sacroiliac disease: comparative evaluation of radiological and radionuclide techniques. J Rheumatol 2:45-5 I, 1975 Namey TC, McIntyre J, use M, LeRoy EC: Nucleographic studies of axial spondylarthritides. rthritis Rheum 20: , 1977 Dequeker J, Goddeeris T, Walravens M, DeRoo M: Evaluation of sacroiliitis: comparison of radiological and radionuclide techniques. Radiology 128: , Goldberg RP, Genant RK, Shimshak R, Shames D: pplications and limitations of quantitative sacroiliac joint scintigraphy. Radiology 128: , Spencer DG, dams FG, Horton PW, uchanan WW: Scintiscanning in ankylosing spondylitis: a clinical, radiological and quantitative radioisotopic study. J Rheumatol 6: , Ho G, Sadovnikoff N, Malhotra CM, Claunch C: Quantitative sacroiliac joint scintigraphy: a critical assessment. rthritis Rheum , Green F: Joint scintiscans: present status (editorial). J Rheumatol 6:37&373, Kozin F, Duquesnoy R, Rodey GE, Lightfoot RW Jr, Ryan LM: High prevalence of HL-CWl and CW2 antigens in spondyloarthritis. rthritis Rheum 21 : , Calen, Porta J, Fries JF, Schurman DJ: The clinical history as a screening test for ankylosing spondylitis. JM 237~ , Carrera GF, Foley D, Ryan LM, Kozin F, Lawson T: Computed tomography of sacroiliitis. m J Roentgen01 136:41-46, 1981

COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF EARLY ANKYLOSING SPONDYLIT-IS

COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF EARLY ANKYLOSING SPONDYLITIS ADEL G. FAM, JOEL D. RUBENSTEIN, HYACINTH CHINSANG, and FRANCES Y. K. LEUNG Computed tomography (CT) was compared with plain radiography