Macroglossia in patients with multiple myeloma is most commonly due to deposition of which substance in the tongue?

In multiple myeloma, macroglossia (enlarged tongue) results from amyloidosis — the deposition of amyloid protein (derived from monoclonal immunoglobulin light chains, especially lambda chains) in the tongue muscle and connective tissue. Multiple myeloma is associated with AL (amyloid light chain) amyloidosis, where the abnormal monoclonal proteins aggregate into insoluble beta-pleated sheet fibrils that deposit in various tissues. The tongue is commonly affected, producing a firm, enlarged tongue with possible 'waxy' papules. Other oral manifestations of multiple myeloma include jaw radiolucencies ('punched-out' lesions), pathological fractures, and hypercalcemia.