Histological Findings in Kidney Biopsies of Patients with Monoclonal Gammopathy—Always a Surprise

Renal outcome in multiple myeloma patients with cast nephropathy: a retrospective analysis of potential predictive values on clinical and renal outcome

OBJECTIVE

Cast nephropathy (CN) is the leading cause of acute kidney injury (AKI) in multiple myeloma (MM). Since it is sparsely documented why some patients with CN do achieve a renal response while others do not, we describe a single-center cohort of patients with multiple myeloma and biopsy-confirmed CN to evaluate potential markers of renal response.

METHODS

The data was collected as a retrospective, single-center analysis of CN-patients treated at the Medical University Vienna between 01/01/2004 and 01/01/2022. Baseline parameters and clinical outcome was compared between renal responders and non-responders.

RESULTS

Among 28 patients with CN, n = 23 were assessed for renal response (14 responders; 9 non-responders). Renal responders were younger (median age: 61 years; 77 years, p = 0.039), showed higher overall survival (153months; 58months, p = 0.044) and achieved hematologic response (≥PR) to first-line therapy (p = 0.029), and complete hematologic response (CR) at any time (p = 0.025) significantly more often. Further, we could show that rapid initiation of anti-myeloma therapy after initial presentation correlated significantly with renal response (median 9 days; 27 days, p = 0.016). Analyses of kidney biopsy specimens revealed that patients with a high IF/TA score showed end stage renal disease (dialysis ≥ 3 months) significantly more often (p = <0.001).

DISCUSSION

In summary, our data suggests, that a rapid start with systemic hematologic treatment in patients with MM and CN is crucial and achieving an early hematologic response is important for renal recovery. Moreover, achieving a deep hematologic response and subsequent renal recovery improves clinical outcome as reflected by an overall survival benefit.

The Urine Light Chain/eGFR Quotient as a Tool to Rule out Cast Nephropathy in Myeloma-Associated Kidney Failure

Kidney involvement with resulting kidney failure leads to increased mortality in patients with multiple myeloma (MM). Cast nephropathy (CN), in particular, if left untreated, quickly leads to kidney failure requiring dialysis and has a very poor prognosis for the affected patient. The gold standard for diagnosing kidney involvement is a kidney biopsy. However, due to bleeding risk, this cannot be done in every patient. We recently reported that a quotient of urine light chain (LCurine) to glomerular filtration rate (eGFR) is a non-invasive diagnostic tool for patients with kidney involvement in MM. But this quotient has not yet been tested in everyday clinical practice. In this study, our LCurine/eGFR ratio was tested on 67 patients in two centers. Enrollment took place between January 2019 and September 2023. A total of 18 of the 67 patients had CN. With the threshold defined in our initial paper, we were able to show a sensitivity of 100% with a specificity of 85.7% for CN in patients with MM. As a result, the LCurine/eGFR quotient recognizes 100% of all CN and can therefore detect this group, which has a very poor prognosis, without the need for a kidney biopsy.

[Electron microscopy in nephropathology]

Non-neoplastic kidney diseases represent a broad spectrum of diseases. Although their pathogenesis differs, the histological findings may be similar in terms of conventional morphology. A precise classification of these diseases is a prerequisite for correct therapy and prognostic assessment. In the diagnostic process, the magnification achieved by electron microscopy is essential and cannot be replaced by any other technique. The most frequent diagnostic questions addressed by ultrastructural studies represent (1) alterations of podocytes (e.g., minimal-change disease), (2) changes of the thickness and structure of the glomerular basement membrane (e.g., diabetic glomerulosclerosis or Alport disease), (3) the presence, characteristics and exact localisation of immune complexes (e.g., membranous glomerulonephritis or lupus nephritis), (4) alterations of endothelial cells and capillaries (e.g., thrombotic microangiopathy) and (5) diseases of the tubular cells (e.g., light-chain nephropathy or toxic effects). Therefore, ultrastructural investigations are-together with conventional microscopy and immunohistochemistry (or immunofluorescence)-an integral part of the so-called triple-diagnostics in routine nephropathology.

Monoclonal Gammopathies of Clinical Significance: A Critical Appraisal

Monoclonal gammopathies of clinical significance (MGCSs) represent a group of diseases featuring the association of a nonmalignant B cells or plasma cells clone, the production of an M-protein, and singularly, the existence of organ damage. They present a current framework that is difficult to approach from a practical clinical perspective. Several points should be addressed in order to move further toward a better understanding. Overall, these entities are only partially included in the international classifications of diseases. Its definition and classification remain ambiguous. Remarkably, its real incidence is unknown, provided that a diagnostic biopsy is mandatory in most cases. In fact, amyloidosis AL is the final diagnosis in a large percentage of patients with renal significance. On the other hand, many of these young entities are syndromes that are based on a dynamic set of diagnostic criteria, challenging a timely diagnosis. Moreover, a specific risk score for progression is lacking. Despite the key role of the clinical laboratory in the diagnosis and prognosis of these patients, information about laboratory biomarkers is limited. Besides, the evidence accumulated for many of these entities is scarce. Hence, national and international registries are stimulated. In particular, IgM MGCS deserves special attention. Until now, therapy is far from being standardized, and it should be planned on a risk and patient-adapted basis. Finally, a comprehensive and coordinated multidisciplinary approach is needed, and specific clinical trials are encouraged.