RADIOLOGIC DIAGNOSIS AND PATHOLOGY OF THE SPONDYLOARTHROPATHIES
Section snippets
SACROILIITIS IN SPONDYLOARTHROPATHIES
The sacroiliac joints may be involved in all SpA subsets but mainly and most severely in AS.34 These joints are either unilaterally or bilaterally affected in the SpA, with an intensity ranging from mild to very severe inflammation, resulting in partial or complete ankylosis. Symmetric sacroiliitis was found in 89% of patients with AS and in 67% of patients with chronic ReA and PsA in longstanding disease, respectively;13 however, the kind of sacroiliac joint involvement has often been
SACROILIITIS AND HUMAN LEUKOCYTE ANTIGEN B27
The association of HLA-B27 with sacroiliitis has been demonstrated in a study of 440 HLA-B27–positive patients with rheumatic diseases. Eighty-three percent of these patients had sacroiliitis.89 In addition to HLA-B27, there are three risk factors for the development of sacroiliitis and AS in patients with SpA: ReA, gut inflammation, and psoriasis.
The prognostic impact of HLA-B27 on the course of SpA was recently indicated by several studies. In a Finnish study on 16 patients who were involved
PATHOGENESIS OF SACROILIITIS
Why the sacroiliac joint? The reason for the tissue tropism in SpA is still obscure. The localization of the sacroiliac joint not far from the bowel has led to various reports and hypotheses on the role of gut inflammation in SpA. By an increased permeability of the gut wall due to gut inflammation found in SpA, 107, 119, 120, 121, 122 bacteria can get access to the bloodstream more easily. For ReA-associated bacteria, it is not clear how frequently infections with enterobacteriae or chlamydiae
DIFFERENTIAL DIAGNOSIS OF SACROILIITIS
Sacroiliitis also occurs in other bacterial infections that can be clinically somewhat similar to SpA. The sacroiliac joints can be affected in tuberculosis and brucellosis.28, 84, 132 In these diseases, bacteria are generally thought to be locally present, probably also in the sacroiliac joints, but this has not been demonstrated. In patients with spinal tuberculosis, bacteria have been detected in biopsy specimens.14, 84 Can something about the pathogenesis of sacroiliitis be learned from
IMAGING OF SACROILIITIS
Objective evidence of an advanced degree of sacroiliitis is critical for the diagnosis of AS163 and important for the differentiation between AS and uSpA.28, 60 In early and acute stages of sacroiliitis, the diagnosis can be difficult because conventional imaging has a limited capacity when no bony changes are yet present. In advanced disease, the sacroiliac joints almost disappear from the radiograph as a result of ankylosis, the very characteristic feature of AS.43, 150, 163 The development
IMAGING OF SPINAL INFLAMMATION
There have been several reviews on conventional radiographic techniques of the spine in the past few decades.12, 43, 55, 66, 71, 134 This review touches these aspects only briefly and concentrates on new imaging techniques, such as MR imaging.87 The characteristic radiologic features of AS are given in Table 1.
Although in advanced stages of disease, syndesmophytes easily detected on lateral spinal radiographs are a rather specific feature of AS, they are not part of the diagnostic criteria for
SPONDYLITIS
In contrast to what was just discussed for sacroiliitis, the situation with spondylitis is different because at the time when spondylitis develops, the diagnosis of AS is usually clear; however, few cases have no or little sacroiliac joint involvement.78, 95 No clear data indicate how often pathologic radiographs of the spine irrespective of sacroiliac changes might contribute to the diagnosis of AS.
Definite structural changes of the vertebral bone occur as spondylitis anterior described by
SPONDYLODISCITIS
Spondylodiscitis has mainly been a radiologic diagnosis since the original description by Andersson in 1937.7 In 1978, Dihlmann and Delling56 differentiated an inflammatory form of spondylodiscitis and a noninflammatory type caused by osteoporotic fractures known to occur in patients with AS with increased frequency.51 According to a recent report, spondylodiscitis occurs in 15% of patients with AS.90 Using MR imaging, the authors have observed spondylodiscitis in 12 of 20 patients with SpA and
IMAGING OF OTHER JOINTS IN SPONDYLOARTHROPATHIES
The temporomandibular joints can be severely and symptomatically affected in patients with SpA, mainly in AS. This was recently demonstrated in a study using MR imaging technology.136 The sternoclavicular joints are frequently affected in 50% of the patients with AS and PsA, of interest, in the absence of palmoplantar pustolosis.67 The palmoplantar pustolosis is a characteristic feature of the SAPHO syndrome, 91 which is generally regarded as an entity separate from SpA, but the overlapping
IMAGING OF ENTHESES AND JOINTS BY ULTRASOUND
Enthesopathy is a very characteristic feature of the SpA. In a Finnish study using the established technique of ultrasonography for the detection of enthesitis, 53 50% of the examined SpA patients had signs of inflammation at the entheses, predominantly in the achillean region.103 Of possible relevance to the management of SpA, ultrasound examinations using 7.5-mHz devices can also be performed to detect synovial effusion; Baker cysts; bursitis, and to some degree, also synovitis and cartilage
OSTEOPOROSIS IN ANKYLOSING SPONDYLITIS
It is quite clear now that osteopenia occurs already in early disease stages of AS167 and that osteoporotic fractures have an increased prevalence in AS.51 The reasons for this are probably the local and systemic inflammation in all stages of disease and the immobility mainly in later stages. Corticosteroids are of minor importance because they are rarely useful in patients with AS. Although bone loss occurs mainly in the center of the vertebrae, syndesmophytes grow at the lateral rim, also in
PATHOLOGY OF SPONDYLOARTHROPATHIES
Sacroiliitis, very often the initial feature of AS, always starts in the iliac part of the sacroiliac joint, which is characterized by fibrocartilage (whereas the sacral part consists of hyaline cartilage).15 This knowledge could give clues to antigenic targets involved, but nothing has been reported so far. The only speciality of ilial cartilage was narrow collagen fibrils arranged parallel to the articular surface observed in an earlier study.130 The sacroiliac joint is irregularly shaped,
HISTOLOGIC STUDIES OF SPINAL INFLAMMATION
More than half of the spinal structures of patients with AS become affected in the course of disease; rarely this happens very early. The progression is usually from the lumbar vertebrae upward but is often irregular.62 Histologic studies on spinal inflammation in AS have used autopsy material62 and specimens obtained at spinal fusion operations.1 Involvement of the spinal skeleton in the SpA is characterized mainly by two essential features: (1) inflammation and (2) new bone formation. The
HISTOLOGY AND IMMUNOHISTOLOGY OF COMPUTED TOMOGRAPHY-GUIDED SACROILIAC BIOPSIES
An important advantage of the CT-guided sacroiliac joint biopsy technique30 is that it can be combined with intra-articular corticosteroid therapy32 (see Fig. 6). Using this method, we found infiltrates of mononuclear cells and islands of beginning ossification in the tissue samples (Fig. 10) of patients with very active disease.30 By semiquantitative immunohistology, we found relatively more CD4+ than CD8+ and a high number of CD14+ macrophages in the inflamed sacroiliac joints in a ratio not
IMMUNOHISTOLOGIC FINDINGS IN PERIPHERAL JOINTS IN PATIENTS WITH ANKYLOSING SPONDYLITIS AND REACTIVE ARTHRITIS
If the peripheral joint involvement in AS and RA is compared, a statement is usually made that there is not much difference, both showing lymphocytic infiltrates, pannus formation, and joint destruction, in AS more markedly in the root joints, hips and shoulders; however, some differences exist: in AS, less erosions and more ankylosis are generally found. Rheumatoid granulomas and vasculitis do not occur in AS. In some cases granulation tissue starting in the underlying bone marrow was
ANIMAL MODELS
Three animal models are possibly relevant for human SpA disease: the HLA-B27 transgenic rat model80 and two HLA-B27 transgenic mouse models, HLA-B27 transgenic mice lacking β2 microglobulin96 and ANKENT, a model of ankylosing enthesopathy of peripheral joints.166
In the rat model, HLA-B2705 and human β2 microglobulin genes were introduced in several strains of Lewis rats. Only the males of the susceptible 21-4H strain showed swelling, erythema, and tenderness of the tarsal joints of one or both
SUMMARY
Five different subtypes of spondyloarthropathy (SpA) are now recognized. Clinical and radiologic involvement of the sacroiliac joint is an outstanding feature of the SpA, especially ankylosing spondylitis (AS). In this partly debilitating form of SpA a unique type of inflammatory axial involvement is observed which is characterized by inflammation and new bone formation at different spinal sites. In longstanding disease sacroiliitis, spondylitis and spondylodiscitis are easily recognized by
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2016, Best Practice and Research: Clinical RheumatologyCitation Excerpt :Other frequent comorbidities of SpA are osteoporosis and cardiovascular disease. Sacroiliitis, spondylitis, aseptic spondylodiscitis, and inflammatory involvement of the posterior elements of the spine are the typical inflammatory manifestations in the axial skeleton in axSpA [4], which later lead to new bone formation, such as syndesmophytes and ankylosis. An estimated 15% of patients with established AS may later develop a so-called “bamboo spine” [5].
Address reprint requests to Jürgen Braun, MD, Section Rheumatologie, Klinikum Benjamin Franklin FV, Hindenburgdamm 30, 12200 Berlin, Germany, [email protected]
Dr. Braun and Dr. Sieper are supported by grant of the German Minister of Research and Technology.