A 18-year-old soldier reported weakness on the abduction of right arm and mild right shoulder pain five days after wearing a rucksack during a 3-day boot camp training (Figure 1-A). After six weeks, he presented hypotrophy of shoulder girdle muscles and winged scapula (Figure 1-B). An electroneuromyography performed at this moment revealed signs of progressive subacute neurogenic motor unit potentials of right deltoid, biceps brachii and anterior serratus (Figure 1-C). Right brachial plexus, shoulder MRI and a viral serum panel were unremarkable.