Acquired rippling muscle disease associated with mild myasthenia gravis: a case report

[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.

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.