A combined method for quantitative pertechnetate scintigraphy in the diagnosis of sacroiliitis. A controlled study

The sacroiliac joints: evaluation using nuclear scintigraphy. Part 2: Lame horses

REASONS FOR PERFORMING STUDY

Sacroiliac (SI) joint disease is difficult to diagnose definitively on clinical grounds.

HYPOTHESES

Lameness not attributable to SI joint pain may result in asymmetrical uptake of radiopharmaceutical in the tubera sacrale and SI joints; and that horses with clinical signs suggestive of sacroiliac joint disease would have differences in the ratios of radiopharmaceutical uptake between the fifth lumbar vertebra (L5) and either the tubera sacrale or SI joints compared with normal horses.

OBJECTIVES

To determine whether differences in radiopharmaceutical activity could identify individuals with presumed SI joint region pain.

METHODS

The scintigraphic appearance of the pelvic region of 234 horses (Group I) with lameness unrelated to the SI joints was compared with that for 40 normal horses (Group N) in full work and that for 41 horses with suspected SI joint disease (Group II). The effect of age, sex, lame limb and discipline were assessed in Group I. Motion-corrected scintigraphic images were assessed grossly, using profile analysis and by comparing ratios of uptake of mean count per pixel between L5 and each of the left (L) tuber sacrale (TS), right (R) TS, LSI and RSI joints. Left-right symmetry was compared.

RESULTS

Lame horses (Group I) had greater asymmetry of radiopharmaceutical uptake in the tubera sacrale compared with normal horses. Horses with right hindlimb lameness had a larger RSI/LSI ratio compared to normal horses. In Group I L5/LTS, L5/RTS and L5/RSI increased with age, and there was a trend for L5/LSI to increase with age. In horses with presumed sacroiliac joint disease (Group II), L5/LTS, L5/RTS and L5/RSI were all greater compared with normal horses. Detection of marked left-right asymmetry by quantitative analysis or profile analysis was helpful in discriminating between those horses with clinical signs compatible with SI joint disease and either normal horses or those lame due to another cause.

CONCLUSIONS AND POTENTIAL RELEVANCE

Scintigraphic evaluation of the SI region is useful to identify SI joint disease in combination with other clinical signs supportive of the diagnosis. However, diagnosis should not be based on this alone because of some degree of overlap in the range of radiopharmaceutical uptake between horses with SI joint disease and both normal horses and those with other causes of lameness.

Imaging of the seronegative spondyloarthropathies

The group of seronegative spondyloarthropathies consists of ankylosing spondylitis, psoriatic arthritis, Reiter's disease, enteropathic spondylitis, and a fifth entity known as undifferentiated spondyloarthropathy. All of these diseases share common clinical and radiographic features with characteristic involvement of the sacroiliac joints, spine, and to various degrees, the peripheral joints. Although plain radiographs are the first line of imaging investigation, they are often insensitive for demonstrating the early changes of sacroiliitis, an important feature for establishing the early diagnosis of seronegative spondyloarthropathy. Other imaging modalities, including conventional tomography, bone scintigraphy, and computed tomography, have improved visualization of inflammatory changes at the sacroiliac joints. This article will review these modalities and emphasize the role of magnetic resonance imaging. By directly imaging changes in the synovium, articular cartilage, and subchondral bone, findings on magnetic resonance imaging are the most sensitive and specific for sacroiliitis and other changes in the axial skeleton. Its role and that of ultrasound in the assessment of the peripheral joints will also be highlighted.

Seronegative spondylarthropathies: imaging of spondylitis, enthesitis and dactylitis

Sacroiliitis is an indispensable condition for the diagnosis of ankylosing spondylitis according to the present criteria and is usually diagnosed on standard anteroposterior radiographs of the pelvis. In cases with suspicious abnormalities (grade 1 of the New York criteria) CT permits the diagnosis since it shows a higher degree of sacroiliitis. MRI is superior to CT in the early diagnosis as it can detect the cartilage abnormalities which precede bony changes. 'Romanus lesions' with 'shiny corners', 'squaring' of the vertebral bodies, syndesmophytes, spondylodiscitis and osteoporosis are the radiological findings of ankylosing spondylitis. The nonmarginal, asymmetric, coarse and broad syndesmophytes of psoriatic spondylitis and spondylitis associated with Reiter's syndrome resemble the flowing bone outgrowths of diffuse idiopathic skeletal hyperostosis (DISH). The ossification of the posterior longitudinal ligament and of the flavum ligament are rare manifestations of ankylosing spondylitis. Peripheral extra-articular enthesitis is a clinical hallmark of seronegative spondylarthropathies. Plain film radiography shows erosions and spurs but only in advanced phases. US shows the swelling of the entheses and the peritendinous soft tissues and the distension of adjacent bursae by fluid collection. MRI shows the inflammation of the bone adjacent to the insertion as well as the soft tissue changes. Dactylitis is another typical manifestation of seronegative spondylarthropathies. In the past it was thought to be due to concomitant tenosynovitis and arthritis. Recently, however, we have demonstrated with US and MRI that the 'sausage-like' appearance is due to the flexor tenosynovitis and that joint capsule distension is not indispensable.