Feline insular amyloid: histochemical distinction from secondary systemic amyloid.

Amyloid in islets of Langerhans from 48 domestic cats, one human, one non-human primate, and one raccoon was compared with secondary systemic amyloid from three domestic cats, one dog, one human, and one cow to determine affinity for Congo red dye after treatment of paraffin-embedded tissue sections with potassium permanganate and dilute sulfuric acid. Insular amyloid from all six species was resistant to pretreatment with potassium permanganate, i.e., affinity for Congo red was retained, whereas secondary systemic amyloid from all species was sensitive to the potassium permanganate pretreatment. Other stains did not distinguish between insular and secondary systemic amyloid. The potassium permanganate-Congo red staining procedure thus can be used to differentiate insular from secondary systemic amyloid in the cat and other species. The results also indicate that insular amyloid and secondary systemic amyloid are of different chemical composition and pathogenesis.