Acute muscle weakness (AMW) is a pediatric emergency. During diagnostic approach, it is crucial
to obtain a detailed anamnesis, including: onset of weakness, history of associated febrile states,
ingestion of toxic substances/toxins, immunizations, and family history. Neurological examination
must be acucious as well. In this review, we describe the most common diseases related to AMW,
grouped into the site of origin (from the upper motor neuron to the motor unit). Early detection of
hyperCKemia may lead to a myositis diagnosis, and hypokalemia orients the diagnosis of periodic
paralysis. Ophthalmoparesis, ptosis and bulbar signs are suggestive of myasthenia gravis or
botulism. Distal weakness and hyporeflexia are clinical features of Guillain-Barre Syndrome (GBS),
the most frequent cause of AMW. If all studies are normal, a psychogenic cause should be
considered. Finding the etiology of AMW is essential to accomplish treatment in a timely manner,
improving the prognosis of affected children.