Immunosuppressive treatment of rippling muscles in patients with myasthenia gravis

[Rippling muscle disease with myasthenia gravis]

In February 2020, a 51-year-old woman experienced leg myalgia and noticed calf muscle movements that resembled a rippling wave while crouching down. In June 2020, she complained of bilateral arm myalgia. In August 2020, she developed left ptosis, had difficulty raising her bilateral arms, and developed diplopia and was admitted to our hospital. Anti-acetylcholine receptor antibodies turned out to be positive. We made a diagnosis of myasthenia gravis and acquired rippling muscle disease (RMD). Her myasthenia gravis symptoms and myalgia decreased with oral prednisolone. Contrast-enhanced computed tomography revealed thymoma. She underwent extended thymectomy and was discharged from the hospital. Her myalgia worsened, but it was responsive to methylprednisolone pulse therapy. CAV3 gene mutations are recognized as causes of congenial RMD whereas acquired RMD is associated with myasthenia gravis. Acquired RMD is rarely reported in Japan, but should be kept in mind as a condition treatable with immunotherapy.

Rippling Muscle Disease with Irregular Toe Jerks and Anti-acetylcholine Receptor Antibodies: Remission after Extended Thymectomy

We herein report a 63-year-old rippling muscle disease (RMD) patient who presented with painless stiffness, muscle hypertrophy and muscle contractions elicited by mechanical stimulation. He also showed irregular toe jerks and a slightly elevated level of anti-acetylcholine receptor antibody (AChR-Ab). Since he had a mediastinal mass mimicking thymoma, which was later revealed to be a bronchial cyst, he underwent extended thymectomy. The irregular toe jerks disappeared within a week after the operation. The other muscle symptoms completely remitted 27 months after the onset. This is the first report of a sporadic case of RMD with irregular toe jerks that resolved after extended thymectomy.

Trouble at the junction: When myopathy and myasthenia overlap

Although myopathies and neuromuscular junction disorders are typically distinct, their coexistence has been reported in several inherited and acquired conditions. Affected individuals have variable clinical phenotypes but typically display both a decrement on repetitive nerve stimulation and myopathic findings on muscle biopsy. Inherited causes include myopathies related to mutations in BIN1, DES, DNM2, GMPPB, MTM1, or PLEC and congenital myasthenic syndromes due to mutations in ALG2, ALG14, COL13A1, DOK7, DPAGT1, or GFPT1. Additionally, a decrement due to muscle fiber inexcitability is observed in certain myotonic disorders. The identification of a defect of neuromuscular transmission in an inherited myopathy may assist in establishing a molecular diagnosis and in selecting patients who would benefit from pharmacological correction of this defect. Acquired cases meanwhile stem from the co-occurrence of myasthenia gravis or Lambert-Eaton myasthenic syndrome with an immune-mediated myopathy, which may be due to paraneoplastic disorders or exposure to immune checkpoint inhibitors.

Immune-mediated rippling muscle disease and myasthenia gravis

Cases of acquired rippling muscle disease in association with myasthenia gravis have been reported. We present three patients with iRMD (immune-mediated rippling muscle disease) and AChR-antibody positive myasthenia gravis. None of them had thymus pathology. They presented exercise-induced muscle rippling combined with generalized myasthenia gravis. One of them had muscle biopsy showing a myopathic pattern and a patchy immunostaining with caveolin antibodies. They were successfully treated steroids and azathioprine. The immune nature of this association is supported by the response to immunotherapies and the positivity of AChR-antibodies.

Identification of skeletal muscle autoantigens by expression library screening using sera from autoimmune rippling muscle disease (ARMD) patients

Novel forms of contractile regulation observed in skeletal muscle are evident in neuromuscular diseases like rippling muscle disease (RMD). Previous studies of an autoimmune form of RMD (ARMD) identified a very high molecular weight skeletal muscle protein antigen recognized by ARMD patient antisera. This study utilized ARMD and myasthenia gravis (MG) patient antisera, to screen a human skeletal muscle cDNA library that subsequently identified proteins that could play a role in ARMD. Based on nucleotide sequence analysis, three distinct ARMD antigens were identified: titin Isoform N2A, ATP synthase 6, and PPP1R3 (protein phosphatase 1 regulatory subunit 3). The region of titin identified by ARMD antisera is distinct from the main immunogenic region (MIR) recognized by classical MG antibodies. Sera from classical MG patient identifies an expressed sequence corresponding to the titin MIR. Although the mechanism of antibody penetration is not known, previous studies have shown that rippling muscle antibodies affect the contractile machinery of myofibers resulting in mechanical sensitivity. Titin's role as a modulator of muscle contractility makes it a potential target in understanding muscle mechanosensitive regulation.

Acquired rippling muscle disease with myasthenia gravis

Rippling muscle disease (RMD) is a rare disorder that occurs in both familial and sporadic forms. Seven patients have previously been reported with myasthenia gravis and sporadic RMD. There have been conflicting reports of the electrophysiological characteristics of rippling muscles in this acquired form. Another such patient is reported, and the clinical, electrophysiological, and laboratory features of this disorder are described. In addition, this patient had alopecia areata and recurrent metastatic thymoma, years after resection of a benign thymoma. This report emphasizes the clinical manifestations of RMD in association with myasthenia gravis (RMD-MG), and its distinctive features, in this and previously reported patients.

Rippling muscle disease: a review

Rippling muscle disease (RMD) is a benign myopathy with symptoms and signs of muscular hyperexcitability. The typical finding is electrically silent muscle contractions provoked by mechanical stimuli and stretch. After the first description in 1975, there have been several publications on this disorder. Although RMD most often is reported with autosomal dominant inheritance, some sporadic cases are found, and an association with other diseases such as myasthenia gravis has also been reported. The pathophysiological mechanism is still not clarified. Abnormalities in calcium homeostasis in the sarcoplasmic reticulum have been proposed as the most probable causes. However, recent genetic studies make a primary channelopathy unlikely. In this article, a review of this curious disease is presented.