ummm we sometimes call them hermits I guess, but I think of old people with long beards living out the midle of no where when I think of the word "hermit". But hikikomori refers to young people, in their teens and 20's, that perfer to be anti-social and cut themselfs off from most everyone else, yes we have that here, I'm kind of like that, but we don't realy have a name for it.
From Wiki: "While there are mild and extreme degrees, the Japanese Ministry of Health defines a hikikomori as an individual who refuses to leave their parent's house, and isolates themselves away from society and family in a single room for at period exceeding six months, though many such youths remain in isolation for a span of years, or in rare cases, decades."