A 28-Year-Old Woman Comes to the Office Due to Stiffness

A 28-year-old woman comes to the office due to stiffness and weakness of her hands over the past several months.  The patient has had decreased grip strength and frequent episodes in which her hands felt so stiff that she could not let go of objects.  She also reports fatigue and excessive sleepiness and says, "I can sleep 20 hours straight and still wake up tired."  The patient has had occasional difficulty with speech, which she describes as mild slurring and a heavy feeling in the tongue.  She has no prior medical conditions and takes no medications.  Vital signs are within normal limits.  Physical examination shows a flat affect and mild bilateral ptosis.  Hand grip is weak bilaterally, and mild atrophy of the small muscles of the hands is present.  Deep tendon reflexes are normal throughout and Babinski sign is absent.  When the patient is instructed to repeatedly close the eyes tightly, there is a noticeable lag when she opens them.  Which of the following is the most likely cause of this patient's current condition?

A) Abnormal production of thyroid hormone
B) Anti-acetylcholine receptor antibodies
C) Cytosine-thymine-guanine trinucleotide repeat expansion
D) Lymphocytic inflammation of the skeletal muscles
E) Progressive fibrosis of multiple organs