Q. A 36-year-old woman presents with weakness of finger abduction and adduction and clawing of digits 4 and 5. She also has mild weakness in wrist flexion on the ulnar side. Sensation is decreased over the palmar and dorsal aspects of the little finger and medial half of the ring finger. The remainder of her upper limb strength and sensation are intact. Which of the following findings would most reliably distinguish this lesion from a C8–T1 root lesion (Klumpke’s palsy)?