Sparing of leprosy macule in ampicillin hypersensitivity rash

A case of tuberculoid leprosy is reported in a middle aged female, who presented with generalised erythematous maculopapular rash which followed ampicillin therapy. In spite of extensive and severe involvement of the skin all over the body by erythema and rash, the hypopigmented patch of leprosy on the face did not show any erythema or rash and stood out more clearly as an island of pale area in the midst of large area of erythema on the face. The possible mechanism of non development of erythema and rash in the patch is discussed.