Monoclonal gammopathy of renal significance (MGRS)-related AL amyloidosis complicated by amyloid myopathy: a case report

Abstract

Background Lately, monoclonal gammopathy of renal significance (MGRS) has been defined as a group of renal disorders that are strongly associated with monoclonal protein, including amyloid immunoglobulin light chain (AL) amyloidosis. Amyloid myopathy is rare (1.5% of all patients with amyloidosis) and the prognosis is poor. Furthermore, only approximately 20% of patients with amyloid myopathy are reported to have renal involvement, indicating a lack of data in the literature. Case presentation Here, we report a rare case of MGRS-related AL amyloidosis complicated by amyloid myopathy that presented with muscle weakness in the upper and lower limbs, neck and fingers, and nephrotic syndrome. Blood, urine, and bone marrow examination revealed monoclonal gammopathy of undetermined significance (MGUS) (Bence Jones protein-lambda). Muscle biopsy of the vastus lateralis muscle demonstrated amyloid proteins in the sarcolemma and in the blood vessel walls on Congo red staining, suggesting amyloid myopathy, and tiny inclusions in fibers on modified Gomori trichrome stain. Although we thought they were reminiscent of nemaline bodies, we could not confirm the nature of this structure. Renal biopsy demonstrated amyloid proteins in the mesangial region, part of the capillary walls, and the blood vessel walls on direct fast scarlet staining. As these amyloid proteins were positive for p-component staining and negative for amyloid A staining, β2-microglobulin, and pre-albumin, and as lambda light chains were positive in the mesangial region, we diagnosed the patient with MGRS-related AL amyloidosis. Although he was treated with melphalan and dexamethasone, his symptoms did not improve. Conclusions AL amyloidosis involving the kidneys and muscles has a poor prognosis, and a delayed diagnosis of amyloid myopathy is common because of its rarity and frequent misdiagnosis, which increases organ function deterioration. Therefore, early detection, therapeutic intervention, and careful follow-up are crucial.

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

“…The type of amyloid should be verified using immunostaining or mass spectrometry because amyloidosis varies across muscles (ATTR or isolated amyloid myopathies) ( 6 ). The involved muscle may exhibit edema and atrophy on MRI ( 7 , 8 ), similar to that noted in the case of IIM. EMG often shows nonspecific myopathic changes, which include spontaneous activity (fibrillation potentials and positive sharp waves) and typical myopathic motor unit action potentials (early recruitment of short-duration and low-amplitude motor unit action potentials); these changes are different from the features of patients with peripheral neuropathy, which is important in differential diagnosis, although neuropathy is often observed in AL amyloidosis-associated myopathy due to direct nerve involvement ( 8 – 12 ).…”

“…The type of amyloid should be verified using immunostaining or mass spectrometry because amyloidosis varies across muscles (ATTR or isolated amyloid myopathies) (6). The involved muscle may exhibit edema and atrophy on MRI (7,8), similar to that noted in the case of IIM. EMG often shows nonspecific myopathic changes, which include spontaneous activity (fibrillation potentials and positive sharp waves) and typical myopathic motor unit action potentials (early recruitment of short-duration and low-amplitude motor unit action potentials); these changes are different from the features of patients with peripheral neuropathy, which is important in differential diagnosis, although neuropathy is often observed in AL amyloidosis-associated myopathy due to direct nerve involvement (8)(9)(10)(11)(12).…”