A 19-year-old man, with a history of mild learning difficulties who had been working in commercial toxic waste recycling for less than 1 year, first developed painful right shoulder and arm weakness at the end of August 2009, which progressed rapidly, and in less than 1 month included neck weakness. At the beginning of December, right arm muscle atrophy in the patient was noticed by members of his family, which prompted him to seek medical attention. A complete neurologic examination and workup was done including brain and spine magnetic resonance imaging, repeated electromyographic examination, toxicology screening, lumbar puncture, and biochemical blood tests. The general medical examination was normal. On neurologic examination, he had a normal mental status. Examination of the cranial nerves showed tongue atrophy and fasciculations; bilateral facial weakness, with the right side worse than the left; severe weakness and atrophy; and fasciculations of the sternocleidomastoids and trapezius, with the right side much worse than left. The remainder of the cranial nerves was normal. Motor examination showed atrophy and severe weakness of the right shoulder and upper arm including supraspinatus, infraspinatus, subscapularis, deltoid, pectoralis, and biceps. He had moderate weakness and atrophy of his right triceps and wrist and finger extensors and flexors, as well as interossei of the hands. There was normal bulk, tone, and strength of his left side and right leg. He was areflexic in the right arm, with mild hypereflexia in the left arm, knees, and ankles, with equivocal plantar responses. The cerebellar examination was normal, with the exception of the right arm, which was not testable. The sensory examination was normal as well as of his gait. The brain and spine magnetic resonance images were normal. Results from the lumbar puncture as well as the detailed biochemical tests and toxicology screen were normal. An electromyographic examination showed normal conduction velocities and normal needle examination of the left arm, left shoulder, and left leg. There was some denervation in muscles of the right leg and severe denervation in muscles of the right shoulder and arm. In March 2010, the patient was suspected of having juvenile-onset ALS and was prescribed treatment with riluzole. In May, he developed dysphagia and dysarthria, leading to anorexia and severe weight loss. In August, a control neurologic examination showed a 36-kg young man with diffuse severe muscle atrophy. Muscle weakness was asymmetric, with profound right upper limb weakness and, to a lesser degree, bilateral leg involvement. The patient rapidly progressed to respiratory failure requiring mechanical ventilation. Repeated neurologic examinations showed no cognitive or sensory symptoms or signs. Although follow-up visits were scheduled, the patient was lost to follow-up. In summary, the patient mostly displayed a lower motor neuron phenotype, with the upper limbs and bulbar regions principally affected. Upper motor neurons seemed to be mildly affected.