Nail biting and picking as a possible cause of longitudinal melanonychia. A study of 6 cases.

Examination of individuals affected by onychotillomania led us to describe a new cause of longitudinal melanonychia (LM) of the finger-nails. Damage of the finger-nails was caused both manually and by chewing. The nail cuticles were usually pushed back, and biting caused pressure damage of the base of the nail. It is likely that finger-nails respond similarly to toe-nails and the matrix melanocytes can be stimulated by trauma. Such stimulation can apparently persist long after cessation of the trauma. Histological examination of the nail plates demonstrated that the pigment was melanin. In the matrix an increase in melanin content of melanocytes was found without melanocytic proliferation. LM due to onychotillomania should not be overlooked.