A rare case of Type 4 Pachyonychia congenita

Pachyonychia congenita (PC) is an uncommon keratinisation disorder with autosomal dominant inheritance. This inherited ectodermal abnormality is characterised by pathognomonic nail deformities and defective keratin production. It typically manifests at birth or develops within a year of birth, as the name suggests. The clinical diagnostic hallmark of PC is the presence of thickened wedge-shaped nails. PC tarda (PCT) is a distinct variant of PC characterised by later onset, usually in the second and third decade of life. Very few cases have been reported in the literature. According to the recent classification of PC, our case had the features of Type 4-PC-K16 (caused by pathogenic variation in KRT16). This case is being reported for its rarity as the patient had onset of lesions at 18 years of age, and to corroborate findings of previous report where sparing of lunula was proposed as a clinical sign to differentiate PCT from other causes of subungual hyperkeratosis.