Fibromyalgia in spondyloarthritis: overlapping symptom or overdiagnosed condition?

Abstract

Fibromyalgia (FM) and spondyloarthritis (SpA) share some overlapping symptoms, such as long-term pain, fatigue and tenderness in soft tissues, which can make distinguishing between these two conditions challenging. However, whether fibromyalgia is overdiagnosed in patients with spondyloarthritis is a nuanced issue and depends on several factors, including clinical assessment and diagnostic criteria. Meta analysis by Joneas et al. shows that the prevalence of FM, among a total of 5214 patients with axSpA, was 16.4% (95% CI 12.3–20.5%). Prevalence varied with axSpA sub-classification: in ankylosing spondylitis: 13.8% (9.1–18.6%); in MRI positive non-radiographic axSpA 20.3% (6.5–34.1%); and ‘clinical’ disease: 11.1% (6.0–16.2%). Overall, around 1/6 patients with axSpA also meet criteria for fibromyalgia. While estimates from individual studies vary, comorbid fibromyalgia represents a considerable burden across all sub-classifications of axSpA (1). Another meta-analysis from Min Son et al. showed that axSpA and FM are more prevalent in women than men (sex ratio 3.2:1.3) (2). Koliko su dobri aktualni kriteriji iz 2010? Several studies have demonstrated that FM in axSpA patients is also associated with peripheral enthesitis, present in up to 55.8% of patients with recently diagnosed axSpA (3). In a study by Olfa et al. fibromyalgia associated factors were advanced age and a late age at the onset of axial spondyloarthritis. In addition to that, disease activity and function parameters (eg, BASDAI, ASDAS-ESR, ASDAS-CRP, BASFI, MASES) were significantly higher in the presence of FM (4). There are several reasons for possible overdiagnosis (symptom overlap, diagnostic challenges, comorbidities, over-reliance on symptom based criteria). Both conditions share some common features, like widespread musculoskeletal pain and fatigue. In SpA, inflammation often causes pain in joints and surrounding tissues, while FM involves generalized pain, usually in soft tissues, along with other systemic symptoms like sleep disturbances and cognitive symptoms (often referred to as “fibro fog”). However, the early stages can sometimes be difficult to differentiate from FM, especially in patients who don’t yet have obvious structural changes on imaging. It is not uncommon for individuals with SpA to also have fibromyalgia. In fibromyalgia, diagnosis is often based on symptom criteria, like widespread pain and tenderness. In patients with SpA, a similar symptom profile can arise from disease flares or inflammation (5). Therefore, differential diagnosis is first step and then excluding diagnosis of FM. Without proper diagnostic tests (like imaging or biomarkers specific to SpA), there might be a tendency to label the condition as FM when pain and fatigue persist. Strategies for managing and potentially preventing long-term pain in SpA remain a critical unmet need. Athough targeted therapies for both conditions may differ, in overlapping situations management should include personalized approach, medications, physical therapy modalities, medical exercise and lifestyle changes. In conclusion, while there is a risk of overdiagnosing fibromyalgia in patients with spondyloarthritis due to overlapping symptoms, a thorough diagnostic process can help ensure accurate diagnosis and treatment. It is essential for healthcare providers to consider the full clinical picture, including history, symptoms, imaging, and lab results, to make a well-informed diagnosis.