Clinical approach to the floppy child : main topic

When evaluating a floppy infant, the first goal should be to distinguish whether the disorder is central or peripheral in origin. Hypotonia with weakness suggests a lower motor neuron lesion, whereas weakness is uncommon in disorders affecting the upper motor neuron except during the acute stage. Evaluation of tone and power should be delayed in the unwell, nutritionally compromised child. Muscle enzymes are rarely helpful in the floppy child, with the exception of the congenital muscular dystrophies and some of the structural congenital myopathies. EMG does not allow a definitive diagnosis but is indispensable in deciding whether there is weakness due to neuromuscular disease, or merely hypotonia from causes in other systems or parts of the nervous system. The most common of the neuromuscular disorders, spinal muscular atrophy (SMA), is now diagnosable by molecular genetic analysis (PCR). Where clinical evaluation suggests complex multisystem involvement (i.e. hypotonia plus) inborn errors of metabolism should be excluded. Children with neuromuscular disorders deserve special attention when it comes to anaesthesia. The term 'benign essential hypotonia' or 'hypotonia with a favourable outcome' should be used with caution and only after compliance with strict diagnostic criteria.