The NY Times has an informative article on this (May 2, 2019). (If the link does not work for you, let me know.)
Several medical papers from Spain, Belgium and Italy described a surge in complaints about painful lesions on patients’ toes, Achilles' heels and soles of the feet. Whether the patients were infected was not always clear, because they were otherwise healthy and testing was limited. Most cases have been reported in children, teens and young adults, and some experts say they may reflect a healthy immune response to the virus.
This NY Times article is a great introduction.
This free article in the April International Journal of Dermatology has a good description and very good pictures.