My son had this exact thing- water filled blisters on hands and feet that itched. He was diagnosed with HFMD, although he never had mouth blisters nor were his blisters painful, only itchy. Interestingly, shortly after having this rash he began to have IBD symptoms of blood and mucous in stools. We suspect whatever the rash was sent his system into over drive and triggered his first flare. He was 16 months at the time.