Nail structure can be changed by primary skin diseases (e.g., see our pages on psoriasis or lichen planus), infections (from fungus, yeast or bacteria), trauma, internal systemic diseases, injury, age-related changes, congenital syndromes, and growths arising in or around the nail unit such as benign tumors, warts, cysts, moles, or skin cancers. Diagnostic tools to determine the cause of the nail disorder include a culture of the nail unit for a bacterial or fungal infection, a scraping of the nail plate to look for fungus or yeast, or a biopsy of the nail where the abnormality is. Infectious causes of nail disorders can be treated with appropriate medications for fungus, yeast, or bacteria. Nail problems caused by psoriasis or lichen planus, inflammatory diseases of the skin and nails, may be more difficult to treat. The most common abnormality of the nail unit is a wart, seen in young and older patients. Depending on the particulars, there are a variety of methods of treatment, both medical and surgical.
Another common abnormality we see of the nail unit is a myxoid cyst which can appear near the nail fold and cause the growth of the nail to form a vertical depression. Often the nail growth improves markedly after treating the cyst.
It is important to report any new dark area that appears in a nail plate and does not resolve. Commonly the dark discoloration is a result of injury and represents blood, but this dark color should be examined by a dermatologist to make sure that a tumor is not present in the nail. A change in color could be indicative of melanoma, a potentially very serious form of skin cancer. Melanoma may present as a dark streak in a nail plate that may extend into the cuticle. A biopsy must be taken, and, if positive for melanoma, surgical excision is the standard treatment. If your nail has a change in color or a streak, it can be critically important that you have this examined by a dermatologist without undue delay.