Amyloid, which appears as pink, amorphous, intercellular material in tissue sections stained with hematoxylin and eosin, can be deposited in any tissue, and may be localized or widespread in its deposition. The most common sites are liver, spleen, adrenal, and kidney, where amyloid is frequently deposited around vascular structures. Amyloidosis is subclassified by the type of proteins that make up the amyloid fibrils. The basic structure of all amyloid types is a β-pleated sheet of fibrils 7.5 to 10 nm wide. Numerous methods can demonstrate the presence of amyloid, but the most specific is Congo Red stain, followed by microscopic examination with polarizing lenses that show a characteristic bright green birefringence. Immunoperoxidase staining is then performed to detect acquired systemic AA amyloidosis .
The most common type of amyloidosis in the USA is immunological. This type is composed of light chains (Bence-Jones proteins) secreted by plasma cells of multiple myeloma [6, 7]. Amyloidosis may also be secondary to chronic inflammatory conditions such as autoimmune diseases, chronic infections, and some neoplasms (for example, Hodgkin's lymphoma and renal cell carcinoma) . The amyloid fibrils in inflammatory conditions are composed of serum amyloid-associated protein. The heredofamilial type of amyloidosis is an autosomal dominant condition .
Pre-operatively, our patient was presumed to have splenic infarct or abscess as the cause of splenic rupture because up to 51% of patients with IE suffer emboli to major organs . During surgery, we questioned that diagnosis when no abscess was seen in the spleen, and the cross-sectioned tissue appeared grossly homogeneous.
Pathological evaluation was consistent with acquired systemic AA amyloidosis, which was previously called secondary amyloid because it was seen secondary to inflammation. This type of amyloidosis is a rare systemic condition that can occur in the context of chronic inflammation in which there is protracted breakdown of cells. This condition is seen most commonly in rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease, and the drug use method referred to as 'skin popping', as in our patient . Skin popping is the injection of narcotics, commonly heroin, just under the skin. Black tar heroin is used on the west coast of the USA and is considerably 'dirtier' than its east coast heroin counterpart. Users tend to have a high incidence of abscess formation, IE, and possibly reactive systemic amyloidosis, as in our patient. The cytokine release during chronic bouts of inflammation is thought to lead to increased production of AA protein in the liver; this protein is then released into the blood stream and deposited in small blood vessels throughout the body. This protein deposition leads to vessels that are delicate and easily disrupted.
Patients who are hospitalized rarely experience ASR. However, septic emboli are common in patients with IE who are hospitalized, occurring in up to 51% . In left-sided endocarditis, these emboli can travel to the spleen and lead to infarction and splenic rupture. Our patient was hospitalized for IE, but pathological evaluation of the spleen revealed no evidence of bacterial embolization, infarction or abscess; therefore, the ASR most likely resulted from systemic AA amyloidosis.