Vacuolar myopathy with monoclonal gammopathy and stiffness (VAMMGAS)

Abstract

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.