Introduction: Pathology requires the integration of macroscopic and microscopic findings for an accurate diagnosis. Fine needle aspiration biopsy (FNA) traditionally became the domain of radiologists with the introduction of ultrasound; however, its increased accessibility has allowed other specialists, including pathologists, to incorporate it into their daily practice. Both ultrasound-guided FNA and core needle biopsy (CNB) performed by interventional pathologists have proven valuable tools in the diagnosis of lymph node lesions. Materials and Methods: An observational, descriptive, retrospective study was conducted at Hospital Universitario del Henares, analysing 134 FNABs and 31 CNBs of lymph node lesions between 2023 and 2024. The diagnostic yield of both techniques and their correlation were evaluated. Results: Ultrasound facilitated better lesion characterization. FNA demonstrated a diagnostic yield of 98%, with a 94% correlation with CNB results. The Sydney system 2020 was applied to FNA reporting in lymphatic node. An equivalent classification system for CNB is proposed. Conclusion: The performance of FNA and CNB by pathologists optimizes diagnosis, reduces time and costs, and strengthens their role in minimally invasive diagnostics. Adoption of a unified classification system for CNB lesions would facilitate communication between specialists.

Background Primary pyomyositis is a rare condition in children that should be included in the differential diagnosis of musculoskeletal infections. Objectives To describe the clinical features of pyomyositis as well as its diagnostic and therapeutic approach. Methods A descriptive and retrospective study was performed by reviewing medical records of patients admitted to our hospital from January 1996 to July 2013 with a diagnosis of primary pyomyositis. Results A total of 25 patients (16 men, 9 women) aged between one month and 14 years (median age 2 years) were registered. Two peaks of incidence have been found in the months of July and October. The most frequent clinical manifestations were the presence of local pain (24 patients), fever (18 patients), local swelling (9 patients) and skin rash (7 patients). Predisposing factors in 8 patients (1 strenuous exercise, 4 trauma, 3 intramuscular injections) were found. The primary site was pelvic muscles or lower extremities (20 patients). In laboratory results, we found the presence of leukocytosis, with an average value of 12,936±5.753/uL leukocytes, total neutrophils 4.659/uL ±7.350), ESR of 55±28 mm) and PCR 8±6 mg/dL). CPK was normal in 5 out of 6 patients who were requested. Laboratory results were positive for Staphylococcus aureus (7 patients), Salmonella no tiphy (1 patient) and Bacteroides fragillis (1 patient). Ultrasound suggested the diagnosis in 11 cases and magnetic resonance imaging support the diagnosis in all cases. All patients received intravenous antibiotic therapy (mean duration 11 days) followed by oral antibiotic therapy (mean duration 23 days). 9 patients suffered complications as abscess formation, 3 need abscess aspiration and one of them required surgical drainage. None of our patients had residual functional limitations. Conclusions It is important to have a high index of suspicion for pyomyositis in patients with fever and musculoskeletal pain at an early stage in order to initiate start appropriate antibiotic treatment against Staphylococcus aureus. Although ESR and ultrasound may be useful, it is necessary to complement with magnetic resonance imaging in order to support the diagnosis in all cases. Disclosure of Interest None declared DOI 10.1136/annrheumdis-2014-eular.4467