A 58-year-old man has experienced worsening double vision and eyelid drooping, particularly toward the end of the day, for 1 month. He also has had difficulty chewing his food at dinner. He was diagnosed with Sjogren syndrome more than a decade ago. On physical examination, he has 5/5 motor strength in his extremities that decreases to 4/5 strength with repetitive movement. Administration of edrophonium restores muscle strength. There is no pain on palpation and no decrease in joint mobility. Which of the following laboratory findings is most likely to be reported for this patient?

Myasthenia gravis leads to muscle weakness from loss of motor endplate function. This disorder is caused by an antibody-mediated loss of acetylcholine receptors at neuromuscular junctions. Edrophonium inhibits cholinesterase to improve synaptic transmission. The anti-Jo-1 antibody is present in polymyositis. Sjogren syndrome does not cause muscle weakness with use. Myopathic diseases such as muscular dystrophies are accompanied by increased levels of serum creatine kinase. Generalized muscle weakness with type II muscle fiber atrophy occurs in glucocorticoid excess. Parasitic infection with Trichinella spiralis can lead to eosinophilia.