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Physicians have developed a new guided approach to biopsy entheseal tissue in patients with psoriatic arthritis (PsA) that allows for molecular and cellular analysis using second harmonic generation microscopy, according to findings published in Annals of the Rheumatic Diseases.
Researchers initially attempted ultrasonography-guided biopsy method on 5 cadavers from which they extracted entheseal tissue from the lateral epicondyles without removing bone. Once they established the technique, they removed the entire entheseal complex including bone, tendon, and muscle for analysis using second harmonic generation microscopy.
During the microscopic tissue analysis, tendons emitted the highest second harmonic generation intensity (91% ± 13%), followed by bone (80% ± 12%), then enthesis with a unique intermediate intensity (31% ± 6%), and lastly muscle (12%±5%).
The researchers determined the optimal cut-off point for isolating entheseal tissue from muscle and tendon after differentiating the tissues according to second harmonic generation intensity. They then successfully obtained a cadaveric biopsy sample that was 68% entheseal tissue.
They repeated the minimally invasive, ultrasonography-guided biopsy approach and extracted 5 mm of tissue from the extensor tendon plate of the elbows of 10 patients diagnosed with PsA. All patients exhibited normal range of motion 2 weeks following the excision, and only mild hematomas in were observed in 2 patients.
The biopsy samples taken from the patients consisted of 65% entheseal tissue, which was close to the 68% composition in the cadaveric biopsies. In contrast, the biopsies from the patients with PsA demonstrated infiltration with CD45+ immune cells.
Rheumatologists can perform this technique to analyze the molecular and cellular changes occurring in their patients with PsA and assess the efficacy of anti-inflammatory treatments for enthesitis.
The researchers concluded, “[E]ntheses display a specific feature of collagen assembly, where type-II collagen fibers display a distinct fibrous organization…. [Second harmonic generation-intensity] signatures…differentiate entheseal from tendon and muscle tissue and, therefore, allow identification of entheseal tissue in small biopsies.”