Limited systemic sclerosis and diffuse systemic sclerosis are two subsets of systemic sclerosis, both of which are autoimmune diseases associated with ACA antibodies. The main difference lies in the extent of skin involvement and internal organ complications. Limited systemic sclerosis primarily affects the skin on the hands, face, and lower arms and is associated with a better prognosis. Diffuse systemic sclerosis involves more widespread skin thickening and more severe internal organ involvement, often leading to a poorer prognosis.