ectopic nail growth (onychoheterotopia)

Last edited 11/2022 and last reviewed 02/2023

Ectopic nail growth (onychoheterotopia)

Ectopic nail (onychoheterotopia) describes the growth of a nail plate in a location other than the usual nail unit, which can be congenital or associated with trauma (1)

• is defined as growth of nail tissue in any site other than the classical nail unit areas (2)
• is usually an acquired condition, though congenital cases can also be seen (3)
• acquired ectopic nail develops either after a single overwhelming trauma or after chronic repetitive injuries, which lead to both splitting and implantation of the germinal matrix or heterotopic inoculation of the oncocytes (nail bed cells) (2)
  • such cases occur predominantly over the dorsal aspect of the hand
  • ectopic nail is mostly deformed, probably, because of the absence of normal nail folds and nail bed, both of which have a favorable modulating influence on nail plate formation (3)
    • if the ectopic nail matrix comes in contact with the periosteum, it may impede intramembranous ossification, producing hypoplasia and thinning of the phalanx
• histopathologically, onychoheterotopia comprises a mature nail unit, including a cornified nail plate and nail matrix (3)
• partial excision, leaving behind the ectopic nail matrix, is frequently associated with recurrences (3)

Management of ectopic nail ranges from observation to excision and is guided by the appearance of the nail, symptom severity, and functional impairment

• standard treatment is surgical excision of the ectopic nail including the ectopic matrix, followed by primary closure of the defect (3)

Reference:

• Anasiewicz N, Morenschlager M. Post-traumatic ectopic nail-like structure BMJ 2022; 379.
• Chatterjee K, Chaudhuri A, Chatterjee G. Onychoheterotopia: a unique case. Indian J Dermatol. 2013 Mar;58(2):150-1.
• Grover C, Kharghoria G. Surgical Management of Onychoheterotopia. J Cutan Aesthet Surg. 2018 Jul-Sep;11(3):140-142.