Abstract
Ankylosing spondylitis (AS) is a chronic inflammatory disease which affects primarily the sacroiliac joints and the spine. In patients with active disease, magnetic resonance imaging (MRI) of the spine shows areas of bone marrow edema, the histopathological equivalent of which is unknown. In this study we correlate inflammation in the spine of patients with AS as revealed by histological examination with bone marrow edema as detected by MRI. We have compared the histopathological findings of zygapophyseal joints from 8 patients with AS (age: 30 to 64, disease duration 7 to 33 years) undergoing spinal surgery with findings in MRI. For histopathological analysis, we quantified infiltrates of CD3+, CD4+ and CD8+ T cells as well as CD20+ B cells immunohistochemically. Bone marrow edema was evaluated in hematoxylin and eosin stained sections and quantified as the percentage of the bone marrow area involved. All patients with AS showed interstitial mononuclear cell infiltrates and various degrees of bone marrow edema (range from 10% to 60%) in histopathological analysis. However, in only three of eight patients histopathological inflammation and edema in the zygapophyseal joints correlated with bone marrow edema in zygapophyseal joints of the lumbar spine as detected by MRI. Interestingly, two of these patients showed the highest histological score for bone marrow edema (60%). This first study correlating histopathological changes in the spine of patients with AS with findings in MRI scans suggests that a substantial degree of bone marrow inflammation and edema is necessary to be detected by MRI.
Highlights
The prevalence of ankylosing spondylitis (AS) within Caucasians has been estimated to be between 0.2% and 0.8% [1,2]
Mononuclear cell infiltration We summarize the results of a semi-quantitative analysis of mononuclear cell infiltration in the bone marrow of zygapophyseal joints as described in the Method section
Microvessel density To address the question of whether hypervascularization might contribute to the detection of bone marrow edema in the spine by magnetic resonance imaging (MRI) we stained CD34+ endothelial cells in our sections
Summary
The prevalence of ankylosing spondylitis (AS) within Caucasians has been estimated to be between 0.2% and 0.8% [1,2]. About 20% of these patients with AS have bridging syndesmophytes which result in restricted movement of the spine as a consequence of active inflammation in spinal joints and adjacent structures [3]. It has been suggested that the involvement of zygapophyseal joints is important in the restriction of spinal mobility [3,4,5]. Acute inflammation in the spine associated with AS, as detected by magnetic resonance imaging (MRI), has been described in the intervertebral disc, in the vertebra, enthesis of AS = ankylosing spondylitis; HPF = high-power field; MR = magnetic resonance; MRI = magnetic resonance imaging; TIRM = turbo inversion recovery magnitude. Systematic MRI of zygapophyseal joints has not been undertaken so far
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