Axial Spondyloarthritis and New Bone Formation

Abstract

Axial spondyloarthritis is an inflammatory disease of the axial skeleton. Its pathogenesis is only partly understood. At the beginning, there are inflammatory changes in the sacroiliac joints which are followed by inflammation in vertebral bodies and in facet joints. Low back pain occurring in the morning hours is the dominant clinical symptom. In the early phase, inflammatory changes are detectably by MRI. Inflammation promotes a process of joint remodelling in the sacroiliac joints which leads to erosions, sclerosis and bony bridging, i. e. ankylosis, which are detectable by X-ray. In the spine, vertical osteophytes developing at sites of previous inflammation connect vertebral bodies as syndesmophytes. Additional ossification of longitudinal ligaments contributes to the so-called bamboo spine. Ossification of the spine promotes fixation of a severe kyphosis of the thoracic spine which strongly impairs spine mobility and quality of life. High disease activity seems a prominent risk factor for development of structural damage. However, although NSAIDs improve clinical symptoms, they do not reduce new bone formation. In contrast, TNFα and IL-17 inhibitors seem to retard new bone formation apart from their clinical efficacy. Research work of the last years identified immunological pathways of inflammation. However, the trigger and cellular components of the immune reaction in the bone marrow are still poorly defined. Osteoclasts are involved in the destruction of the subchondral bone, while osteoblasts facilitate new bone formation and cartilage ossification. This review gives an overview about diagnostics and therapy of axSpA and about risk factors for the development of structural damage. Concepts about the immune pathogenesis and joint remodeling in AS are given under recognition of genetic and histopathological studies.

Zusammenfassung

Die axiale Spondyoarthritis ist eine entzündliche Erkrankung des Achsenskeletts, deren Pathogenese nach wie vor nur in Ansätzen verstanden ist. Initial finden sich entzündliche Veränderungen in den Sakroiliakalgelenken, im weiteren Verlauf kommt es zu Entzündungen in den Wirbelkörpern und im Bereich der Facettengelenke. Klinisch im Vordergrund stehen morgentlich auftretende, tiefsitzende Rückenschmerzen. Die entzündlichen Veränderungen sind in der Frühphase der Erkrankung im MRT nachweisbar. Durch die Entzündung wird ein Gelenkumbau in den Sakroiliakalgelenken initiiert, der Erosionen, Sklerosierungen und knöcherne Durchbauungen, d. h. Ankylosen, nach sich zieht, die radiologisch darstellbar sind. Im Bereich der Wirbelsäule bilden sich an entzündeten Wirbelkörperkanten vertikale Osteophyten, die als Syndesmophyten zur knöchernen Verbindung von Wirbelkörpern führen. Außerdem kommt es zur Ossifikation der Längsbänder, was zum Vollbild der sog. Bambuswirbelsäule beiträgt. Die Knochenneubildung und Ossifikation im Bereich der Wirbelsäule mit Fixierung einer oft ausgeprägten Brustkyphose führt zu einer erheblichen Einschränkung der Wirbelsäulenbeweglichkeit und Beeinträchtigung der Lebensqualität. Eine hohe Krankheitsaktivität scheint ein wesentlicher Risikofaktor für die Entwicklung dieser strukturellen Schäden zu sein. Allerdings haben NSAR trotz Besserung der klinischen Beschwerdensymptomatik keinen hemmenden Einfluss auf die Knochenneubildung. TNFα-und IL-17-Inhibitoren scheinen neben der guten klinischen Wirksamkeit auch die Knochenneubildung zu verzögern. Forschungen der letzten Jahre konnten immunologische Signalwege der Entzündung identifizieren, wobei die Trigger und zellulären Komponenten der Immunreaktion im Knochenmark noch unverstanden sind. Osteoklasten sind an der Destruktion von subchondralem Knochen beteiligt, während Osteoblasten Knochenneubildung und Knorpelossifikation vermitteln. Dieser Beitrag gibt einen Überblick über Diagnostik und Therapie der axSpA sowie Risikofaktoren für die Entwicklung struktureller Schäden. Es werden Konzepte der Immunpathogenese und des Gelenkumbaus bei der AS unter Einbeziehung genetischer und histopathologischer Studien dargestellt.

Key words

axial spondyloarthritis - ankylosing spondylitis - radiographic progression - new bone formation

Schlüsselwörter

axiale Spondyloarthritis - ankylosierende Spondylitis - radiographische Progression - Knochenneubildung

Publication History

Received: 09 July 2021

Accepted: 25 August 2021

Article published online:
18 November 2021

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