Axial Spondyloarthritis: Mimics and Pitfalls of Imaging Assessment

Pseudolesions involving bone and soft tissue regarding orthopedic oncology

Pseudolesions in bone and muscle are encountered mostly incidentally in routine imaging studies, especially due to the recent advancements on many different imaging modalities. These lesions can be categorized into the following categories: normal variants; congenital; iatrogenic; degenerative; and postoperative. In this review, we discuss the many different radiological characteristics of musculoskeletal pseudolesions that appear on imaging, which can prevent non-essential additional studies.

Predominant ligament-centric soft-tissue involvement differentiates axial psoriatic arthritis from ankylosing spondylitis

Since the original description of spondyloarthritis 50 years ago, results have demonstrated similarities and differences between ankylosing spondylitis (AS) and axial psoriatic arthritis (PsA). HLA-B27 gene carriage in axial inflammation is linked to peri-fibrocartilaginous sacroiliac joint osteitis, as well as to spinal peri-entheseal osteitis, which is often extensive and which provides a crucial anatomical and immunological differentiation between the AS and PsA phenotypes. Specifically, HLA-B27-related diffuse bone marrow oedema (histologically an osteitis) and bone marrow fatty corners detected via magnetic resonance imaging, as well as radiographic changes such as sacroiliitis, vertebral squaring, corner erosions and Romanus lesions, all indicate initial bone phenotypes in HLA-B27+ axial disease. However, in much of PsA with axial involvement, enthesitis primarily manifests in ligamentous soft tissue as 'ligamentitis', with characteristic lesions that include para-syndesmophytes and sacroiliac joint bony sparing. Like axial PsA, diffuse idiopathic skeletal hyperostosis phenotypes, which can be indistinguishable from PsA, exhibit a thoracic and cervical spinal ligamentous soft-tissue tropism, clinically manifesting as syndesmophytosis that is soft-tissue-centric, including paravertebral soft-tissue ossification and sacroiliac soft-ligamentous ossification instead of joint-cavity fusion. The enthesis bone and soft tissues have radically different immune cell and stromal compositions, which probably underpins differential responses to immunomodulatory therapy, especially IL-23 inhibition.

Paraneoplastic sacroiliitis

A man in his early 70s presented with stiffness and aching in the shoulder and pelvic girdles. His C reactive protein level was elevated at 116 mg/L, leading to an initial diagnosis of polymyalgia rheumatica. Treatment with prednisone at 20 mg/day provided limited improvement and relapses recurred despite concomitant immunosuppressive agents. Extensive investigations failed to reveal an underlying aetiology.Five years later, gross painless haematuria led to the detection of an invasive papillary urothelial carcinoma. A review of the staging CT scan revealed findings compatible with bilateral erosive sacroiliitis, which had developed since his initial presentation. Radical cystoprostatectomy provided temporary relief but after a further 9 months, symptoms relapsed, and metastatic spread was discovered.Paraneoplastic sacroiliitis is a rare clinical entity; and to the best of our knowledge, this is the first reported case associated with a solid tumour.

MRI Findings in Axial Psoriatic Spondylarthritis

Psoriatic arthritis is a significant medical condition with a high prevalence, a wide variety of non-specific symptoms, and a high degree of overlap with other spondylarthritis disorders, particularly ankylosing spondylitis. Hence, knowledge of the magnetic resonance imaging (MRI) manifestations and a multidisciplinary strategy are required for the better management of these patients. We searched publications from the last 10 years and focused on the most relevant ones which discussed the classification criteria, the MRI characteristics of axial psoriatic arthritis, the importance of MRI for follow up, and the reliability of skin and synovial biopsy. Axial spondylarthritis can be diagnosed and followed up on using the well-established MRI technique and, additionally, a biopsy. The analysis and concordance between them can provide new directions for future studies.

Spondyloarthritis and nonbacterial thrombotic endocarditis as paraneoplastic manifestations in treatment-naive Burkitt lymphoma

Non-radiographic axial spondyloarthropathy (nr-axSpA) is a clinical diagnosis of symptoms matching inflammatory back pain criteria without radiological lesions at the sacroiliac joint. The frequency of an early nr-axSpA-like presentation in lymphoma patients has not been clarified. Here we report a woman in her 20s with a fever and musculoskeletal discomfort. Detailed investigations revealed that she was suffering from Burkitt lymphoma in which nr-axSpA-like symptoms were a musculoskeletal manifestation of the disease, irrelevant to the anti-neoplastic treatment.

The value of magnetic resonance imaging and computed tomography in the study of spinal disorders

Computed tomography (CT) and magnetic resonance imaging (MRI) have replaced conventional radiography in the study of many spinal conditions, it is essential to know when these techniques are indicated instead of or as complementary tests to radiography, which findings can be expected in different clinical settings, and their significance in the diagnosis of different spinal conditions. Proper use of CT and MRI in spinal disorders may facilitate diagnosis and management of spinal conditions. An adequate clinical approach, a good understanding of the pathological manifestations demonstrated by these imaging techniques and a comprehensive report based on a universally accepted nomenclature represent the indispensable tools to improve the diagnostic approach and the decision-making process in patients with spinal pain. Several guidelines are available to assist clinicians in ordering appropriate imaging techniques to achieve an accurate diagnosis and to ensure appropriate medical care that meets the efficacy and safety needs of patients. This article reviews the clinical indications of CT and MRI in different pathologic conditions affecting the spine, including congenital, traumatic, degenerative, inflammatory, infectious and tumor disorders, as well as their main imaging features. It is intended to be a pictorial guide to clinicians involved in the diagnosis and treatment of spinal disorders.

Future of Low-Dose Computed Tomography and Dual-Energy Computed Tomography in Axial Spondyloarthritis

Purpose of Review

Recent technical advances in computed tomography (CT) such as low-dose CT and dual-energy techniques open new applications for this imaging modality in clinical practice and for research purposes. This article will discuss the latest innovations and give a perspective on future developments.

Recent Findings

Low-dose CT has increasingly been used for assessing structural changes at the sacroiliac joints and the spine. It has developed into a method with similar or even lower radiation exposure than radiography while outperforming radiography for lesion detection. Despite being incompatible with low-dose scanning, some studies have shown that dual-energy CT can provide additional information that is otherwise only assessable with magnetic resonance imaging (MRI). However, it is unclear whether this additional information is reliable enough and if it would justify the additional radiation exposure, i.e. whether the performance of dual-energy CT is close enough to MRI to replace it in clinical practice.

Summary

While the role of dual-energy CT in patients with axial spondyloarthritis remains to be established, low-dose CT has developed to an appropriate modality that should replace radiography in many circumstances and might supplement MRI.