ABSTRACT

The term chromonychia may indicate a trifold abnormality in the color of the substance and/or the surface of the nail plate and/or the periungual tissues.

Examination of abnormal nails should be done with the ngers completely relaxed and not pressed against any surface. To differentiate between discoloration of the nail plate and the vascular nail bed, the ngertip should be blanched to determine if the pigmented abnormality is grossly altered. If the pigment originates from the blood vessels (e.g., in methemoglobinemia), it will usually disappear. If the pigmentation is not altered in the blanching test, it may be obliterated by a penlight pressed against the pulp, meaning that the pigment is deposited in the nail bed; the exact position of the discoloration can then be identied more easily. All digits are usually involved when pigmentation is due to systemic absorption of a chemical through the skin. When the cause is endogenous, the discoloration often corresponds to the shape of the lunula (Figure 5.1). By contrast, when the discoloration follows the shape of the proximal nail fold (PNF) (Figure 5.1), it corresponds to the stigmata of an external contactant. In that case, nger pressure producing blanching does not alter the pigmentation, nor does a penlight placed against the nger pulp. The discoloration can sometimes be removed by scraping or cleaning the nail plate with a solvent like acetone. To determine if the color is within the nail, a piece of it should be excised and examined while it is immersed in water. In deeper or subungual impregnation of the nail keratin, microscopic studies (potassium hydroxide [KOH], periodic acid-Schiff [PAS] stain) may be indicated.