What happened to Phoenix's grandson that is the reason for her repeated trips to twon in the story, A Worn Path?

Phoenix's grandson does not appear in the story, but his medical condition is the reason for the old woman's journey. Having swallowed lye (a strong alkaline substance used in making soap) several years ago, the boy's throat is permanently damaged. His grandmother is the only relative he has left, and she makes the trip to town to receive medicine that soothes the pain.