Heavy Chains, Heavy Consequences: A Case of Concomitant Heavy Chain Amyloidosis and Heavy Chain Deposition Disease.

Heavy chain (AH) amyloidosis is a rare form of primary systemic amyloidosis that predominantly affects the kidneys and can lead to nephrotic syndrome. It is marked by the deposition of amyloid fibrils derived from immunoglobulin (Ig)-heavy chains. Monoclonal immunoglobulin deposition disease is a similarly rare disorder involving deposition of nonfibrillar and Congo red-negative monotypic Ig molecules in basement membranes. It can be derived from Ig light chains, Ig heavy chains, or Ig light and heavy chains. Cases of combined amyloidosis and monoclonal immunoglobulin deposition disease are exceedingly rare. Only a handful of concomitant amyloidosis and heavy chain deposition disease have been previously reported, and the spectrum of such diagnoses is poorly described. We describe a case of concomitant IgG4-type AH amyloidosis and heavy chain deposition disease in an 83-year-old man with a history of Agent Orange exposure who developed nephrotic syndrome resulting in diuretic-resistant anasarca. A subsequent bone marrow biopsy demonstrated a λ-restricted plasma cell population. The patient was initiated on hemodialysis and chemotherapy, resulting in clinical stabilization. This case report also contrasts AH amyloidosis with other forms of amyloidosis, emphasizing its unique clinical features, diagnostic challenges, and management considerations.