Emergence of proteinase 3-antineutrophil cytoplasmic antibody-associated glomerulonephritis with mesangial immune deposition during the clinical course of IgG λ monoclonal gammopathy of uncertain significance

Patients with monoclonal gammopathy of uncertain significance (MGUS) is sometimes associated with renal diseases, usually due to the deposition of secreted monoclonal immunoglobulin or a fragment thereof, a condition which is defined as monoclonal gammopathy of renal significance. Patients with MGUS appear to be at increased risk for various autoimmune conditions. We report the case of a 68-year-old man developed nephritic syndrome and mild renal insufficiency during the course of IgG λ MGUS. Laboratory findings showed hypocomplementemia, cryoglobulinemia, proteinase 3-antineutrophil cytoplasmic antibody (PR3-ANCA) positivity and monoclonal proteins (λ light chain and λ-Bence-Jones protein) in the urine. A kidney biopsy revealed crescentic glomerulonephritis with mesangial immune deposits without paraproteins. Treatment with prednisolone for ANCA-associated glomerulonephritis, normalized urinalysis and decreased PR3-ANCA but MGUS persisted. This is a rare case of PR3-ANCA-associated glomerulonephritis with comorbid IgG λ MGUS with various pathological paraproteins. We highlight it as a clinical example with diagnostic and therapeutic implications.

Multiple Myeloma and Vasculitic Neuropathy: An Unusual Presentation

Multiple myeloma (MM) is a clonal proliferation of plasma cells in the bone marrow resulting in the production of paraproteins. It is more common in elderly adults and presents with nonspecific symptoms like bone pain, pathological fracture, fatigue, and signs of hypercalcemia. Peripheral neuropathy is an atypical presentation. We present a rare case of vasculitic neuropathy (VN) who was also diagnosed with MM at the same time. Nerve conduction study and biopsy showed findings suggestive of demyelinating VN. His serum protein electrophoresis and bone marrow aspirate were consistent with MM. The association between these two conditions remains understudied. So far there is no strong evidence suggesting an association between MM and VN. If VN was just coincidental or a presenting symptom of MM remains a question and warrants further studies.

A Case of Myeloma Kidney with Perinuclear Anti-Neutrophil Cytoplasmic Antibody and Anti-Myeloperoxidase Positivity: The Importance of Determining the True Cause of Renal Impairment

Acute kidney injury (AKI) is a common presentation which can result from a number of different underlying pathological processes. Haematological malignancies, particularly multiple myeloma (MM), are known to frequently present with AKI. Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a rare condition which can cause crescentic glomerulonephritis (GN), resulting in AKI. We present the case of a 60-year-old man who presented with clinical features suggestive of AAV in the context of blood tests which demonstrated AKI and positive perinuclear ANCA (p-ANCA) and anti-myeloperoxidase (anti-MPO) titres. Further investigations demonstrated an underlying diagnosis of MM. A renal biopsy was ultimately required to determine the cause of AKI, a cast nephropathy. This case is the first to our knowledge which demonstrates a rare situation in which myeloma kidney is associated with positive p-ANCA and anti-MPO titres, without any evidence of a crescentic GN. It highlights the importance of following up on all investigations sent in the context of AKI, even when a potential diagnosis seems evident. Furthermore, it demonstrates the role of renal biopsy in confirming a diagnosis in the context of AKI with multiple differential diagnoses.

A Case Report of Multiple Myeloma Associated With Myeloperoxidase and Proteinase-3 Antibodies Posing a Diagnostic Dilemma

Multiple myeloma (MM) is a clonal proliferation of antibody-producing plasma cells that can precipitate renal injury through multiple mechanisms. Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an inflammatory condition that can result in renal failure through mononuclear cell infiltration and consequent destruction of glomeruli. Several case reports have identified clinical situations where differentiating these entities has been challenging. Renal biopsy is an invaluable tool in differentiating between MM and AAV when clinical uncertainty exists. We report the case of an 85-year-old man who presented with a rapid decline in renal function and serologies positive for both MM and AAV. Renal biopsy findings confirmed the diagnosis of myeloma kidney and excluded vasculitis. This case highlights an unusual clinical scenario in which both proteinase-3 (PR-3) and myeloperoxidase (MPO) antibodies are positive. While these antibodies are both individually associated with ANCA vasculitis, they are seldom simultaneously positive. Our case would suggest that positive PR-3 and MPO antibodies should raise concern for an alternative diagnosis. Indeed, ANCA, PR-3, and MPO antibodies can all be positive in patients with monoclonal gammopathy in the absence of vasculitis. Our case underscores the value of renal biopsy in the setting of MM.

New aspects on the pathogenesis of renal disorders related to monoclonal gammopathies

BACKGROUND

Multiple myeloma and other related monoclonal gammopathies are frequently encountered conditions associated with renal damage, especially in elderly population. They are arising from clonal proliferation of plasma cells in bone marrow producing various quantities of abnormal monoclonal immunoglobulins, or their components/fragments.

SUMMARY

These abnormal proteins differ from normal immunoglobulins in the amino acid sequence and in the three-dimensional structure of the molecule, which may determine their toxicity. Kidney seems to be a target organ as a major catabolic site. The pathology of renal disease is highly heterogeneous involving a variety of different mechanisms, which are divided into immunoglobulin dependent and immunoglobulin independent mechanisms. The Ig-dependent mechanisms may involve the four components of the kidney parenchyma, and the primary structure of these proteins determine the pattern of renal disease.

KEY MESSAGE

This review summarizes the existing literature in the pathobiology of multiple myeloma, and the pathological properties of the M-proteins, focusing on the mechanisms of the renal manifestations related to these abnormal proteins, especially glomerular injury. Also it supports the opinion that monoclonal gammopathy of undetermined significance (MGUS) should not be used in cases where there is proven renal impairment due to these proteins, even if it is mild and does not meet the current criteria.