Organ malfunction develops as normal tissue is encroached upon by amyloid deposition. There are systemic and localized forms of amyloidosis. Localized forms of amyloid can develop from hormone precursors including proinsulin in the pancreas and precalcitonin in the thyroid gland. Localized amyloid is uncommon in dogs and cats with the exception of pancreatic amyloid deposition in cats. Primary amyloid is derived from the light chains of immunoglobulin in patients with plasma cell tumors, although not all patients with plasma cell tumors develop amyloid.
Primary amyloid is rare in dogs and cats.
Secondary amyloidosis is also called reactive amyloidosis. Secondary amyloidosis usually occurs in patients which have a chronic infectious, inflammatory, or neoplastic disease. Chronic elevation of SAA alone is inadequate to produce amyloid. The location of amyloid deposition in the kidneys differs between dogs and cats and results in different clinical signs in the two species. In the dog kidney, amyloid is deposited adjacent to the glomerular basement membrane resulting in a disruption of the filtration barrier and development of proteinuria.