Background: Intra- and juxta-articular osteoid osteomas are rare, representing less than 10% of all osteomas. Compared to the classic diaphyseal or metaphyseal site of long bones, they often have an atypical onset, a longest diagnostic delay, and frequent initial misdiagnoses, with pictures that can mimic inflammatory monoarthritis. We aimed to describe a case series, and to provide a literature review of this uncommon and misleading tumor location. Methods: We performed a retrospective analysis of patients referred to three pediatric rheumatology centers, with a final diagnosis of articular osteoid osteoma. A review of the literature was additionally conducted. Results: We included 10 patients with a mean age of 14 years. All patients with unusual sites (olecranon fossa, lumbar vertebra, distal phalanx of the toe, fibula) had a misdiagnosis, and cases with initial suspicion of monoarthritis had the longest diagnostic delay, up to 24 months. The literature review confirms the significant risk of misdiagnosis, and an average time from symptom onset to diagnosis ranging from 0.4 to 1.8 years. Conclusions: Articular osteoid osteoma may mimic arthritis, especially in adolescence. Knowledge of the atypical forms of presentation, and of the clinical and radiological pitfalls, reduces the risk of diagnostic error.

Juvenile fibromyalgia (JFM) is a chronic pain condition affecting children and adolescents, often accompanied by emotional distress. Evidence suggests that autonomic dysregulation, as measured by reduced heart rate variability (HRV), may play a key role in symptom expression. This study aimed to explore clinical, emotional, and physiological differences between children with and without JFM. This observational cross-sectional study enrolled 30 participants aged 8 to 17, divided into two equal groups based on JFM diagnosis according to ACR 2010 criteria. Clinical evaluation included Widespread Pain Index (WPI), Symptom Severity Scale (SSS), Numerical Rating Scale (NRS), and the Multidimensional Anxiety Scale for Children – Second Edition (MASC-2). HRV coherence was measured using the emWave Pro system. Group comparisons were analyzed using non-parametric Wilcoxon tests. Correlations were assessed with Spearman’s rank-order test, and logistic regression was used to examine HRV as a predictor of JFM. Children with JFM showed significantly higher levels of pain and anxiety compared to controls (p < 0.001), and significantly lower HRV coherence (mean 0.91 vs. 1.27; p < 0.01). Inverse correlations were found between HRV and symptom severity (WPI, SSS) as well as anxiety levels. Reduced HRV coherence is associated with greater symptom burden and psychological distress in children with JFM. These preliminary findings suggest that HRV may represent a potential biomarker in pediatric fibromyalgia, but larger and more robust studies are required before drawing firm conclusions. HRV biofeedback may offer a supportive, non-pharmacological approach for improving autonomic regulation and managing chronic pain in youth. Not applicable. This observational study was not registered as it did not involve a healthcare intervention.

Background and Objective: Clavicular pain and swelling in children can have multiple causes and often require a multidisciplinary approach. We aimed to describe the characteristics and final diagnoses of children with clavicular involvement and to review the literature on this topic. Methods: We retrospectively reviewed patients younger than 18 years who were evaluated for clavicular symptoms at two pediatric rheumatology centers and one pediatric oncohematology center. These data were then descriptively compared with findings from 63 patients reported across 7 published articles. Results: Twelve patients (9 females, median age 10 years [IQR 9.4–10.5]) were included. Final diagnoses were chronic nonbacterial osteomyelitis (CNO; 8), Langerhans cell histiocytosis (LCH; 2), reactive arthritis (1), and Tietze syndrome (1). Clavicular involvement was mostly unilateral and localized to the medial clavicle in CNO. The most frequent presenting symptom was local swelling (11/12), followed by pain (9/12). Diagnostic delay was a median of 4 months (IQR 1–10.5). Whole-body MRI revealed multifocal lesions in 6/8 CNO patients. Biopsy was often required for diagnosis primarily to exclude malignancy and to clarify atypical or unifocal presentations. The literature review confirmed CNO as the most frequent cause, followed by rare tumors. Conclusions: CNO predominates among pediatric non-traumatic clavicular lesions, but LCH and rare conditions are not uncommon, underscoring the need for careful differential diagnosis and targeted imaging.