Background: Multiple myeloma (MM) is a malignant neoplasm associated with kidney involvement in nearly half of
the patients. Cast nephropathy, monoclonal immunoglobulin deposition disease (MIDD), and light chain (AL) amyloidosis
are the most common monoclonal immunoglobulin-mediated causes of renal injury.
Cardiac involvement is also present in MM, characterized by restrictive cardiomyopathy generated by light chain
deposit or amyloid. Thromboembolic complications such as deep vein thrombosis or pulmonary embolism are also
Case presentation: We present an unusual multidisciplinary case of a woman with a newly diagnosed MM associated
with severe proteinuria and high natriuretic peptide. A renal and fat pad biopsy with Congo red staining were
performed but amyloid deposition was not discovered. While immunofluorescence on fresh frozen unfixed tissue was
not contributory, the immunofluorescence on fixed tissue and electron microscopy revealed the correct diagnosis.
During subsequent investigations, two intracardiac right-sided masses and massive pulmonary embolism were also
Conclusions: This case highlights that multiple organ involvement in patients with MM may result from a combination
of paraprotein-dependent and -independent factors. Moreover, renal diseases induced by monoclonal gammopathies
are a group of complex and heterogeneous disorders. Their subtle presentation and their potential multiorgan
involvement require the expertise of a multidisciplinary team able to provide the most appropriate diagnostic
and therapeutic assessment.
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