Case Report: Monoclonal Gammopathies of Clinical Significance-Associated Myopathy: A Case-Based Review

Monoclonal Gammopathy of Undetermined Significance with Associated Necrotizing Myopathy: A Case Report and Review of the Literature

Background

Monoclonal gammopathies encompass many types of plasma cell proliferative disorders ranging from benign to malignant. Monoclonal gammopathies that meet diagnostic criteria for monoclonal gammopathies of undetermined significance (MGUS) but with clinical manifestations are now being referred to as monoclonal gammopathies of clinical significance (MGCS). MGUS associated myopathies are a rare form of MGCS.

Case description

We present a case of MGUS associated necrotizing myositis. The patient had been previously diagnosed with MGUS and myositis around the same time, but prior testing had not revealed the etiology of the myopathy. Repeat biopsy and work-up revealed a necrotizing myopathy.

Discussion

MGUS associated myopathies are rare, with the most common being sporadic late-onset nemaline myopathy (SLONM-MGUS) and amyloid light chain (AL) amyloidosis-associated myopathy. MGUS associated necrotizing myopathy is even rarer. Because this condition is so uncommon, there are no standardized guidelines on how to treat this condition. Some case reports or studies suggest treating the myositis with standard of care for the myositis type without considering the monoclonal gammopathy while other studies have suggested that treating the monoclonal gammopathy would be beneficial in treating the associated clinical syndrome.

Conclusion

Our case report of MGUS associated necrotizing myopathy encourages internists to broaden their differential diagnosis of myopathy, increasing awareness of a condition that is still not well understood.

LEARNING POINTS

Monoclonal gammopathy of clinical significance is a new term that refers to nonmalignant monoclonal gammopathies that exhibit significant clinical manifestations.Monoclonal gammopathy associated myopathies are rare but should be considered as part of the differential diagnosis for myopathy.

Vacuolar myopathy with monoclonal gammopathy and stiffness (VAMMGAS)

BACKGROUND

Monoclonal gammopathy (MG) has been reported in association with numerous neurological disorders but the spectrum of MG-associated myopathies remains poorly described.

OBJECTIVE

To report a newly acquired myopathy associated with MG.

METHODS

Three adult patients with the same phenotype from two French referral centers were prospectively analyzed. Clinical, electrophysiological, muscle biopsy data, and patients' outcomes under treatment are reported.

RESULTS

The patients, aged 37, 46, and 56 years, presented progressive weakness with subacute worsening and stiffness, in the context of severe weight loss. The weakness mainly involved the proximal limbs and axial muscles. Creatine kinase levels were 1400-2900 IU/L and electromyography revealed a myopathic pattern with spontaneous complex repetitive discharges. Muscle biopsies showed vacuoles containing glycogen and autophagic material along with the presence of sarcolemmal complement membrane attack complex deposits. There was no evidence of a genetic glycogen metabolic disorder. IgGκ monoclonal gammopathy was identified in all cases, without signs of lymphoplasmocytic proliferation. All patients improved with a treatment combining corticosteroids, intravenous immunoglobulins, and immunosuppressants, and two patients recovered walking ability.

CONCLUSION AND RELEVANCE

We report a new muscle disease defined by a vacuolar myopathy characterized by axial and proximal muscle weakness with prominent stiffness and high frequency discharges on electromyography associated with monoclonal gammopathy, defined under the acronym VAMMGAS.

Evaluation of Sarcopenia in Patients with Monoclonal Gammopathy of Undetermined Significance

Background: We aimed to determine the prevalence of sarcopenia in patients with monoclonal gammopathy of undetermined significance (MGUS) and to evaluate the links between MGUS and sarcopenia. Methods: Eighty-two patients with a diagnosis of MGUS were enrolled in the study. Muscle strength was measured using the handgrip dynamometer. Physical performance was assessed by assessing gait speed over a 6-minute walking test. Muscle mass was determined using a bioelectrical impedance analyzer. Results: Sarcopenia was confirmed in 34.15% of patients. Male predominance was demonstrated in MGUS subjects with sarcopenia, particularly patients with low hand grip strength, low appendicular skeletal muscle mass (ASMM), or low ASMM index (p < 0.001, 0.013, and 0.001, respectively). Higher age and lower serum free light-chain Lambda levels were shown in MGUS patients with low muscle function scores compared to normal scores (p < 0.001, and 0.014, respectively). In addition, having a low ASMM score was related to low body mass index and high-risk group (p = 0.020, 0.033, respectively). Conclusions: We demonstrated that the frequency of sarcopenia is high in patients with MGUS. Whether sarcopenia has a possible role as a factor contributing to the pathogenesis of MGUS should be supported by further studies containing longitudinal data.

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.