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

Abstract

We report the case of a 64-year-old man who was sent to our outpatient clinic after experiencing muscle stiffness for 1 year. The stiffness started in his lower limbs and had spread to the inner side of his upper arms over several months. Two months prior to presentation, he suddenly noticed ‘rolling’ muscle contractions in his upper legs, which he had never experienced before. He described these contractions as ‘wave-like’ and could provoke them by manual compression of his quadricep muscles. Except for mild diplopia when driving his car backwards, he denied having other symptoms, especially muscle weakness. His medical history was notable only for a heart attack in 1993, and he took no medication. There was no family history of a neuromuscular disorder. General physical examination was unremarkable. Cranial nerve examination, sensory examination, reflexes, and coordination were normal. Motor examination revealed a painless, involuntary, longitudinal rolling muscle contraction after direct percussion of the quadriceps that lasted only for a few seconds. Laboratory testing revealed a mild increase in creatine kinase (286 U/L). Nerve conduction studies and needle examination were normal. The wave-like contractions as observed in our patient are pathognomonic for rippling muscle disease (RMD). RMD is a rare, often benign and non-progressive neuromuscular disorder characterized by mechanically triggered involuntary rolling muscle contractions. Other clinical symptoms are muscle stiffness, cramps, muscular hypertrophy, focal mounding, referred to as myoedemaand percussion-induced rapid contractions clinically identical to percussion myotonia. Laboratory testing often reveals an elevated serum creatine kinase [1]. Both genetic and sporadic forms of RMD exist. Most patients have a autosomal-dominantly inherited genetic form. At least two distinct loci are reported: the caveolin-3 gene and an undefined locus at 1q41–q42 [1]. Acquired or immuno-mediated RMD is associated with myasthenia gravis. This association was first described in 1996 and in the last decade a small number of case reports followed (Table 1) [2–7]. Immuno-mediated RMD is clinically indistinguishable from hereditary RMD. In our patient genetic tests revealed no mutation in the caveolin 3-gene. Anti acetylcholine receptor antibodies were positive. A second EMG showed no signs of a neuromuscular transmission disorder and on computerized chest-tomography no thymic enlargement was noted. We concluded that our patient suffered from immunomediated RMD with an almost asymptomatic myasthenia gravis. Several features support the immuno-mediated etiology in our patient: an onset in late adulthood, no family history of neuromuscular disorder, no mutation in the caveolin-3 gene and the presence of antibodies against the acetylcholine receptor. In 1999 two patients where described in whom the rippling had preceded the symptoms of myasthenia gravis. In one of these patients, the rippling even started before the antibodies against the acetylcholine receptor could be detected in the serum [5]. These findings S. M. van Schaik V. I. H. Kwa (&) Department of Neurology, Slotervaart Hospital, Louwesweg 6, 1066 EC Amsterdam, The Netherlands e-mail: Vincent.Kwa@slz.nl