Abnormal nail morphology Nail dystrophy SNOMEDCT_US:87065009 HP:0008397 Poor nail formation HP:0008382 HP:0008404 Onychodystrophy UMLS:C0221260 MEDDRA:10028698 HP:0008408 Onychodystrophy is a widely used, yet rarely defined term. Onychodystrophy can be caused by congenital nail diseases, systemic disorders, fungal and nonfungal infections, various noninfectious inflammatory dermatologic diseases of the nail unit and tumors. Onychodystrophy can also occur secondarily to systemic drug use. Onychodystrophy (nail dystrophy) refers to nail changes apart from changes of the color (nail dyschromia) and involves partial or complete disruption of the various keratinous layers of the nail plate. Dystrophic nails