Poorest country in middle America

I guess you mean Central America (the "bridge" between Mexico and South America), excluding the Caribbean islands.

If you only mean Central America, the poorest is Nicaragua, with a Human Development Index (HDI) of 0.699 (for comparison purposes, US and Canada's HDI values are 0.956 and 0.966, respectively).

If you include the Caribbean islands, Haiti (HDI = 0.532) is the poorest country in the Americas.