Congenital onychodysplasia of the index fingers: a case involving the thumbnails.

A case of congenital onychodysplasia of the index fingers involving the nails of both thumbs is presented, and the characteristics and various hypotheses of this most distal congenital reduction malformation are reviewed. The presence of such an atypical case as this may suggest that there is heterogeneity of this congenital condition, in agreement with Ohtsu's classification of this condition into (1) common type, (2) secondary type, and (3) hereditary type. An abnormal hand grip hypothesis, proposed by the author, could not be substantiated by Ohtsu, although it cannot be denied, for instance, based on the presence of a sucking blister. Three groups of congenital distal malformations can be differentiated by the pattern of involved fingers.