[The differential diagnosis of facial paralysis in the newborn: congenital hypoplasia of the depressor anguli oris and depressor labii inferioris muscles (author's transl)].

Six cases of congenital hypoplasia of the depressor anguli muscle and the depressor labii inferioris muscle are described. Hypoplasia of these muscles causes facial asymmetry in the newborn on crying and smiling, since the affected side of the lower lip cannot be drawn down and outwards. This frequently leads to the false diagnosis of partial facial palsy. Electromyography is helpful in the differential diagnosis by detection of the hypoplasia. In contrast to current opinion in the relevant literature, the authors believe that it is hypoplasia of the depressor labii inferioris muscle which is particularly responsible for the clinical picture, rather than merely hypoplasia of the depressor anguli oris muscle.