A 47 year old man, develops symptoms of weakness in his hands, unsteady gait and inability to dorsiflex his foot. He has also developed a tremor of his extremities, slurred speech and difficulty swallowing. As the muscles of the diaphragm weaken, a respirator is needed to help with breathing. After an extensive work-up, you arrive at a diagnosis of Amyotrophic Lateral Sclerosis (ALS). He has no family history of this disease. What is the most likely additional symptom he may develop as this disease progresses?