A44-year-old man starts to notice that his eyelids are drooping. some time afterwards, his jaw becomes weak. he has difficulty swallowing and also experiences weakness in his limbs. he is quite embarrassed when he eats because he must use his hand to support his jaw. his weakness gets progressively worse. finally, he seeks medical attention. his physical examination demonstrates the weakness in his limbs; however, no sensory defects are present. a tensilon test is done and is positive. his doctor is concerned about an associated malignancy. question what is the most likely underlying pathology of these symptoms?