A 19-year-old man comes to the physician for a 4-month history of frequently burning himself on the stove without realizing it until later. He describes diminished awareness of hot and cold sensations in his upper extremities. On examination, he has bilateral muscle wasting of the hand muscles, with decreased strength when gripping objects. Neurologic testing shows absent pain and temperature sensation across both shoulders and arms, while vibration and position sense remain intact. Reflexes are brisk in the upper extremities. He denies trauma, but recalls that his symptoms began gradually and have steadily worsened. Which of the following is the most likely diagnosis?
A) Chiari type I
B) Chiari type II
C) Dandy-Walker
D) Lou-Gehrig disease
E) Sirenomelia
