Wikipedia defines the Dark Ages as lasting through the 15th century, by which point, Islamic medical advancements would have made it into Europe. Obviously, in 500AD, they didn't yet exist.

One of the reason for the decline of the term "dark ages" is that there is increasing evidence that people in this period didn't actually crawl under a rock of ignorance. Large-scale armies and infrastructure projects were gone, but at the same time, a lot more knowledge persisted than is given credit for -- the sorts of things which don't require a massive Roman central government administration to maintain.