Background: Hereditary hemochromatosis (HH) is a common autosomal-recessive inherited disorder that frequently causes arthritis. The pathophysiology of musculoskeletal involvement is however unclear.
Objective: To analyze synovial tissue obtained at surgery of patients with hemochchromatosis arthropathy and compare them with rheumatoid arthritis (RA) and osteoarthritis (OA) specimens qualitatively and quantitatively.
Methods: Synovial tissues of 15 HH patients, 20 RA patients and 39 OA patients were obtained during surgery. A synovitis grading system was used to determine the severity of synovial inflammation. Using immunohistochemistry, synovial neovascularization and infiltration of macrophages, neutrophils and lymphocytes was quantitatively assessed.
Results: Synovitis in hemochromatosis arthropathy largely resembles OA with mild infiltration of mononuclear cells and lymphocytes, decent formation of synovial microvessels and low degree of synovial hyperplasia. While many features of hemochromatosis arthropathy are reminiscent of OA, macrophage and especially neutrophil invasion is clearly more prominent in hemochromatosis arthropathy than in primary OA and mimics features of RA. This finding was especially observed in synovial tissue of hemochromatosis samples with marked haemosiderin deposition.
Discussion: The histological picture of the synovium in hemochromatosis arthropathy largely resembles a process reminiscent of osteoarthritis. Neutrophil invasion is however markedly increased in hemochromatosis arthropathy especially in joints with iron deposition. Accumulation of neutrophils may be crucial for production of matrix enzymes, which enables cartilage degradation and more rapidly progressing articular damage.