Background In a prospective necropsy study of the sternoclavicular joints of 31 unselected subjects (15 female, 16 male; mean age 71 years, range 23–92) to ascertain the prevalence of the features of osteoarthrosis, 29 (93.5%) showed bilateral localised amyloidosis as detected by alkaline Congo red with apple-green dichroism in polarised light. These amyloid deposits were characterised by immunohistological and lectin histochemical techniques.

Methods Amyloid deposits were noted in synovial stroma, in the intra-articular fibrocartilaginous disc and in hyaline articular cartilage (usually superficial and middle zones). In synovial stroma only, there were related accumulations of CD68 positive mono-and multinucleated cells (37% of cases). All amyloid deposits stained with anti P-component antibody. None stained with anti AA monoclonal antibody. Ninety per cent of deposits stained with anti Beta2 microglobulin antibody, 74% with anti lambda antibody and 61% with anti kappa antibody (all monoclonal antibodies). Mixed patterns of immunoreactivity were noted.

Results For lectin histochemical studies sections were probed with a panel of 14 biotinylated lectins using techniques standardised in our laboratory. Chondrocytes (including clones) in all layers of articular cartilage and in disc cartilage showed positive cytoplasmic reactions with HHA (Hippeastrum hybrid agglutinin). In addition PSA (Pisum sativum agglutinin) stained particularly the territorial and interterritorial matrices of hyaline articular cartilage in relatively normal and osteoarthrotic cases. E-PHA (Phaseolus vulgaris erythroagglutinin) selectively stained the neomatrix in osteoarthrotic cases.

Conclusion These results showed a high prevalence of localised amyloidosis in the sternoclavicular joint which is not only an age-related phenomenon but is also related to osteoarthrosis, being particularly marked in fibrillated cartilage. A large number of deposits contained Beta2-microglobulin mixed with lambda and kappa light chains and the ubiquitous P-component. Beta2-microglobulin amyloidosis is a feature of dialysis amyloid arthropathy. None of the cases in this series were on any form of dialysis and none had impairment of renal function of clinical significance. Light chain amyloidosis usually shows a clonal restriction related to plasma cell dyscrasia/proliferation; the polyclonality and the mixed chemical nature of the amyloidosis reported here is unusual. The lectin profiling showed clear cytoplasmic and matrical differences indicating the presence of non-reducing terminal alpha-mannosyl residues in the former and bi/tri antennary non-bisected complex N-linked glycans in the latter. Cartilage neomatrix expressed bi/tri antennary bisected complex N-linked glycans. There was no particular relationship between glycan expression and the amyloid deposits. It has been suggested¹ that the presence of particular glycosaminoglycans in cartilage favours localised amyloidosis either by playing a role in the folding of amyloidogenic proteins in fibril formation or protecting established amyloid deposits from proteolytic degradation. The present results would not support this hypothesis.

Reference

1. Athanasou NA, West L, Sallie B, Puddle B. Localised amyloid deposition in cartilage is glycosaminoglycans-associated. Histopathology 1995;26:267–72