A 5-year-old boy presented with single dystrophic thumb nail since last seven months. Mother gave history of constant biting of thumb nails. On examination, there was median split of right thumb nail with transverse furrows extending form longitudinal split (Fig. 1). All other investigations were non-contributory. He was also diagnosed to have attention deficit hyperactive disorder (ADHD).

Fig.1 Dystrophic thumb nail with medlan split.

Median canaliform dystrophy of Heller (solenonychina, dystrophia unguis mediana canaliformis, nevus striatus unguis) is an uncommon and rare dystrophic condition of nail plate which usually affects thumb nails symmetrically and is characterized by a midline defect of the nail plate leading to longitudinal splitting in the midline with canal formation. It extends from cuticle of nail and shows transverse furrows extending laterally from longitudinal splitting giving characteristic inverted fir tree appearance. It may rarely involve toe nails and other finger nails.

The proposed etiopathogenesis is repeated self inflicted trauma in form of 2habitual nail biting. In the majority of cases the cause is unknown and it may revert back to normal after many months to years. Other proposed that there is also absence of keratinocytes adhesions within nail matrix with dyskeratosis which is responsible for formation of longitudinal grove with splitting of nail plate due to weaker tensile strength. There are some case reports of median canaliform dystrophy of Heller after using retinoids and with familial occurrence. Subungual tumors like glomus tumor, myxoid tumors, papilloma, squamous cell carcinoma, and melanoma may form longitudinal groove and then splitting the nail plate in the middle portion leading to median canaliform dystrophy.