Cardiac and pleuropulmonary AL amyloid imaging with technetium-99m labelled aprotinin

Abstract

Antiproteases are known to be present in amyloid deposits. We evaluated the possibility of using an anti-serine protease (aprotinin) labelled with technetium-99m (TcA), usually employed as a cortical renal tracer, for the imaging of amyloid deposits. Because of the known high uptake of TcA by the kidneys, we limited our analysis to extra-abdominal amyloid localizations. We report the scintigraphic findings observed in 24 patients with light chain amyloidosis (AL) and one with a hereditary form who were known or suspected to have extra-abdominal involvement. Planar scans obtained 100min after i.v. TcA administration showed myocardial accumulation in 11 patients, pleuropulmonary accumulation in nine, pericardial accumulation in two and localization in the neck region (thyroid, salivary glands and tongue) in eight. TcA scintigraphy was negative in five patients without clinical or laboratory evidence of extra-abdominal involvement, as well as in 12 control group patients with cardiac and renal diseases. These preliminary results indicate TcA to be a low-cost, readily available radiopharmaceutical for imaging of extra-abdominal involvement in AL type amyloidosis.

Definition of organ involvement and treatment response in immunoglobulin light chain amyloidosis (AL): A consensus opinion from the 10th International Symposium on Amyloid and Amyloidosis

“…A biopsy specimen should stain positively with Congo red and demonstrate apple-green birefringence under polarized light [13]. Although radionuclide imaging studies using technetium-labeled aprotinin [14] or iodinated serum amyloid P (SAP) component scans [15,16] can be used to image deposits, these are not a substitute for histologic characterization of amyloid deposits and are not widely available [17].…”

Light-Chain (AL) Amyloidosis

“…The aggregates form protofilaments that associate into amyloid fibrils (7). In all types of amyloidosis, glycosaminoglycan moieties of proteoglycans and serum amyloid P (SAP) (8) protein interact with the amyloid fibrils or deposits, promoting fibril formation and stability in tissue (6). Organ dysfunction results from disruption of tissue architecture by amyloid deposits.…”

“…However, quantitative assessment is not possible with this agent, and strongly positive scintigraphic images usually occur only in patients with severe disease, in whom echocardiography generally is diagnostic. Preliminary results suggest that technetium-labeled aprotinin may be more sensitive for imaging amyloid deposits than technetium Tc 99m pyrophosphate (8). Quantitative scintigraphy also can be performed with 123 I-labeled SAP (8) component, a molecule that binds to all types of amyloid (29).…”

Amyloidosis

“…49 Aprotinin scintigraphy has been used successfully for the identification of cardiac involvement in AL amyloidosis. 50 A disadvantage of this tracer, however, is the potential infectious risk, because it is a polypeptide derived from bovine lung tissue. Technetium Tc 99m pyrophosphate and diphosphonate sometimes bind to amyloid and have been used as imaging agents in amyloidosis, especially for detecting cardiac involvement in ATTR amyloidosis (Fig.…”