Background: Monoclonal serum free light chains (sFLC) are a well-known cause of renal impairment (RI) in patients with multiple myeloma (MM). As an indicator of monoclonality, sFLC ratio has acquired a key role in the diagnosis and monitorization of the disease. However, its interpretation is altered in patients with chronic kidney disease (CKD). This study aims to evaluate the modification of the sFLC ratio reference range in patients with CKD, and propose an optimal range for patients with CKD. Methods: Serum FLC κ/λ ratio and estimated glomerular filtration rate (eGFR) were retrospectively analyzed in 113 control patients (without hematologic disease), 63 patients with MM in complete remission and 347 patients with active MM. The three groups included patients with CKD (eGFR < 90). Results: In the group of patients without active MM (n = 176), the sFLC ratio increased at different stages of CKD without pathological significance, with an increase in the number of false positives specially when eGFR is ≤55 ml/min. An optimal range was established for patients with eGFR ≤55 ml/min/1.73 m2: 0.82–3,6 with maximum sensitivity + specificity for that group with an improvement in the Area under the curve (AUC), 0.91 (0.84–0.97) compared with the current ranges proposed by Katzmann and Hutchinson. Conclusions: This study confirms the influence of eGFR on the interpretation of the sFLC ratio, showing a decreasing specificity in progressive CKD stages when using the reference sFLC range (Katzmann), especially in patients with eFGR ≤55. According to our results, we suggest a modified optimal range (0.82–3,6) for eGFR ≤55 ml/min/1.73 m2. It is necessary to validate this modified range in larger and prospective studies.

Monoclonal gammopathy of undetermined significance (MGUS) is defined as the presence of a monoclonal protein (M-protein) produced by a small amount of plasma cells. The majority of patients remain asymptomatic; however, a fraction of them develop clinical manifestations related to the monoclonal gammopathy despite not fulfilling criteria of multiple myeloma or other lymphoproliferative disorder. These patients constitute an emerging clinical issue coined as monoclonal gammopathy of clinical significance (MGCS). The mechanisms involved are poorly understood, and literature is scarce regarding management. The clinical spectrum involves symptoms related to renal, neurologic, skin, ocular, or bleeding manifestations, requiring a multidisciplinary approach. Treatment strategies rely on the basis of symptomatic disease and the M-protein isotype. In this review, we focus on MGCS other than renal, as the latter was earliest recognized and better known. We review the literature and discuss management from diagnosis to treatment based on illustrative cases from daily practice.

Immunoglobulin light-chain (AL) amyloidosis is a systemic disease characterized by the production and deposition of light chain-derived amyloid fibrils in different organs. Prompt treatment directed to the underlying plasma cell clone is crucial in order to achieve a rapid, deep and durable hematologic response. The decrease in the production of the amyloidogenic light chains is a required condition to obtain the organ response, which is commonly delayed. Meanwhile, supportive treatment is aimed to maintain quality of life of these patients and preserve their involved organs’ function. From simple measures, such as salt restriction or compressive stockings, to very complex interventions, such as heart transplantation in very selected patients with isolated severe cardiac involvement, this supportive care is essential and has to be necessarily included in the multidisciplinary management of this disease.

Systemic AL amyloidosis is a challenging disease for which many patients are considered frail in daily clinical practice. However, no study has so far addressed frailty and its impact on the outcome of these patients. We built a simple score to predict mortality based on three frailty-associated variables: age, ECOG performance status (<2 vs. ≥2) and NT-proBNP (<8500 vs. ≥8500 ng/L). Four-hundred and sixteen consecutive newly diagnosed patients diagnosed at ten sites from the Spanish Myeloma Group were eligible for the study. The score was developed in a derivation cohort from a referral center, and it was externally validated in a multicenter cohort. Multivariate analysis showed that the three variables were independent predictors of survival. The score was able to discriminate four groups of patients in terms of overall survival and early mortality in both cohorts. Comorbidity was also analyzed with the Charlson comorbidity index, but it did not reach statistical significance in the model. A nomogram was created to easily estimate the mortality risk of each patient at each time point. This score is a simple, robust, and efficient approach to dynamically assess frailty-dependent mortality both at diagnosis and throughout follow-up. The optimal treatment for frail AL amyloidosis patients remains to be determined but we suggest that the estimation of frailty-associated risk could complement current staging systems, adding value in clinical decision-making in this complex scenario.

Monoclonal gammopathy of undetermined significance (MGUS) is a highly prevalent disorder characterized by a small bone marrow plasma cell or lymphoplasmacytic clone (less than 10%) that produces a small amount of monoclonal paraprotein without associated organ damage. Most patients with MGUS display benign behavior indefinitely, but some progress to an overt malignancy, and others develop organ damage despite no increase in monoclonal protein, resulting in the so-called MG of clinical significance (MGCS). This concept includes different disorders depending on the organ involved, and among them, MG of neurological significance (MGNS) constitutes a real challenge from both a diagnostic and therapeutic point of view. Diagnosis is particularly difficult due to MGNS's heterogeneous clinical presentation and common lack of a diagnostic biopsy. On the other hand, the complexity of treatment lies in the lack of standardized regimens and the common irreversibility of neurological damage. Focusing on the neurological manifestations of MGUS affecting the peripheral nervous system, we describe 3 illustrative cases from daily practice and discuss different aspects of diagnosis to treatment, emphasizing the need for multidisciplinary management based on the close collaboration of neurologists and hematologists.

We analyzed 171 patients with asymptomatic IgM monoclonal gammopathies (64 with IgM monoclonal gammopathy of undetermined significance—MGUS and 107 with smoldering Waldenström macroglobulinemia - SWM) who had a bone marrow (BM) evaluation performed at diagnosis. Abnormal free-light chain ratio (53% vs. 31%) and MYD88 mutation prevalence (66% vs. 30%) were higher in patients with SWM. No other differences were found among groups. With a median follow-up of 4.3 years, 14 patients progressed to Waldenström macroglobulinemia, 1 to amyloidosis, and 28 died without progression. The MYD88 mutation was found in 53% of patients (available in 160 patients). Multivariate analysis showed that immunoparesis (subhazard ratio—SHR 10.2, 95% confidence interval—CI: 4.2–24.8; p < 0.001) and BM lymphoplasmacytic infiltration ≥ 20% (SHR: 6, 95% CI: 1.6–22.1; p = 0.007) were associated with higher risk of progression. We developed a risk model based on these two risk factors. In the absence of both variables, an ultra-low risk group was identified (SHR 0.1, 95% CI 0.02–0.5; p = 0.004), with 3% and 6% of cumulative incidence of progression at 10 and 20 years, respectively. Bootstrap analysis confirmed the reproducibility of these results. This study finds immunoparesis and BM infiltration as biomarkers of progression as well as a low-risk group of progression in asymptomatic IgM monoclonal gammopathies.