Clinical and neurophysiological characteristics of congenital myasthenic syndromes presenting in early infancy

The congenital myasthenic syndromes (CMS) constitute a group of genetic disorders, which affect neuromuscular transmission, presenting usually within the first years of life and with a clinical spectrum ranging from mild muscle weakness to severe disability with life-threatening episodes. We present clinical and neurophysiological data of 11 patients (four males, seven females) with CMS diagnosed during the last 5 years. Eight of the 11 patients presented immediately after birth and the remainder by 10 months of age; eight patients had contractures at birth and seven of them required assisted ventilation either immediately in the neonatal period, or at some point afterwards due to respiratory distress or recurrent apnoeas. Neurological signs at presentation were: in nine patients profound hypotonia, in five absent tendon reflexes, in seven ptosis and in eight bulbar signs. In six patients an edrophonium test was performed: only three of them had a positive response; however, eight out of 11 patients responded at least partially at some point in their illness to pyridostigmine. Diagnosis of CMS was confirmed either by demonstration of a decrement after repetitive nerve stimulation or by increased instability and jitter after stimulated single fibre EMG. In five patients, there was a positive family history with death of at least one previous sibling with an undiagnosed neuromuscular disorder. As regards final outcome, five patients died at ages ranging from 1 to 17 months, two patients are still ventilator-dependent at 3 and 5 months of life, respectively, and four patients still survive with either a mild or a moderate motor delay (follow-up range 8–38 months). None of the clinical or neurophysiological characteristics were correlated with outcome (Fisherʹs exact test). We conclude that a significant number of CMS patients may present in the neonatal period with a variable clinical expression and usually with a poor prognosis. The recognition of specific clinical constellations combined with a search for aetiology at a molecular level will enable the further characterisation of subgroups of CMS.