The combination of chronic bilateral ophthalmoplegia and limb weakness is characteristic of neuromuscular junction disorders and some myopathies, namely mitochondrial myopathies, oculopharyngeal muscular dystrophy, oculopharyngodistal myopathy and congenital myopathies (e.g. centronuclear myopathy and multi-minicore disease). In this case, the clinical presentation, laboratory studies and EMG findings were consistent with a chronic myopathy with congenital onset. Given the decremental response with RNS, a congenital myasthenia might have been considered. However, a previous muscle biopsy was suggestive of centronuclear myopathy, which was confirmed genetically. Defects in neuromuscular junction transmission are indeed increasingly recognised in some congenital myopathies and may respond to treatment.