Aquired Ectopic Nail or Onychoheterotopia.

Sir,

A fresh case of posttraumatic acquired ectopic nail is described, the diagnosis of which was made on the basis of its morphological characteristics, affecting the right index finger nail of a farmer. Ectopic nail (onychoheterotopia) is a growth of the nail tissue on any site other than the classical nail unit areas. It is an extremely rare condition, and most of the reported cases have been congenital and/or associated with other congenital anomalies (e.g. Pierre Robinson syndrome, anomalies of chromosome 6).[1] Posttraumatic ectopic nail has infrequently been reported. It is a fascinating entity which probably results from the traumatic inoculation of nail matrix at another site.[23] The presented case developed an ectopic nail proximal to the normal nail of the right index finger, following a penetrating trauma, while working on his fields.

A 50 year-old-man, farmer by profession had reported with a slow growing hard, white, nail like-structure on the index finger of his right hand for the past 4 months. It had its onset after sustaining trauma at the site. The nail grew like his other nails and required regular trimming. However, the condition was otherwise asymptomatic. He had no complaints pertaining to the underlying joint. Examination of the skin was marked by an easily identifiable nail plate. It was semi-lunar in shape, much like the other normal nails. It was located proximal to the normal nail of the right index finger [Figure 1], and seemed to grow distally towards the normal nail. There were folds of skin, akin to proximal and lateral folds of a normal nail seen surrounding it proximally and on both sides. The surface of the nail plate was rough with presence of longitudinal and deep transverse ridges, extending to the center of the plate. No cuticle was visible. The cuticle of other nails was prominently ragged. There was no visible rudimentary digits were conspicuous by their absence. Examination of skin mucosae and other systems was normal.

Figure 1

Ectopic nail affecting the dorsa of the index finger

Ectopic nail, the onychoheterotopia is an extremely rare disorder, in which the nail tissue grows outside the classic nail unit of the dorsal fingers and toes. It may either be congenital or acquired the former out numbering the later.[1] Its pathogenesis is largely elusive. Acquired ectopic nail is usually an outcome of trauma to the nail unit which may in turn result in transfer of inoculation of the nail matrix, causing the ectopic nail growth.[234]

Whereas, the congenital ectopic nail may either be because of an ectopic existence of germ cells or the nail of a rudimentary or hidden polydactyly.[56] It may also be a part component of Pierre Robin syndrome[7] and an aberration of the long arm of chromosome 6.[378] A genetic inheritance has also been suggested.[39] Furthermore, the congenital is most often seen on the palmar aspect of the fifth digit, followed by the palmar aspect of the fourth, first, third and the second digits.[51011] while the Posttraumatic form is most often seen on the dorsal aspect of the hand.[1] Its presence in extra-digital site is rarer.

The ectopic nail by and large is asymptomatic, however, it may have accompanying irritation and pain should the nail be not cut or trimmed regularly.[1] It may grow horizontally, simulating normal nail, vertical growth of is also identified in places were incomplete or lack of a proper nail fold or nail bed. Circumferential pattern is also known.[13] The ectopic nail is similar to the normal nail histopathologically, but the molecular make up differs.[51213]

Pain, irritation, infection and interference with growth of the distal normal nail, due to impingement onto its matrix[1] are its complications. Surgical excision of the nail and its entire matrix followed by primary closure of the defect is its treatment. Occasionally, a wide defect may result following excision, which is required to be managed by a skin flap or a V-Y advancement flap.[14]