A longitudinal pigmented band in the nail, also call longitudinal melanonychia (LM), is often a diagnostic dilemma for dermatologists. The potential causes of LM are many, but its potential signal for melanoma warrants efforts to seek a precise diagnosis.
Portland, Ore. - A longitudinal pigmented band in the nail, also call longitudinal melanonychia (LM), is often a diagnostic dilemma for dermatologists. The potential causes of LM are many, but its potential signal for melanoma warrants efforts to seek a precise diagnosis.
“A nail matrix biopsy should be performed on any unexplained longitudinal pigmented band in the nail in a Caucasian to rule out melanoma,” says Phoebe Rich, M.D., a dermatologist and nail specialist in Portland, Ore.
Nail band causes
The most important cause of LM is melanoma. Nevus and matrical melanotic macule (the nail equivalent of lentigo) are far more common than melanomas. Most cases of longitudinal melanonychia are due to benign activation of melanocytes, which are normally dormant in the nail matrix. The bands may be solitary, or multiple digits may be involved.
“Pigmented bands in multiple digits are usually a reassuring sign, unless one of the bands is different from all of the rest,” Dr. Rich says. “There are many exogenous causes of benign pigmented bands in the nail, including medications, friction, trauma, foreign body, nail-biting (and) radiation therapy.”
Endogenous factors that have been reported to be associated with benign nail pigmented bands include vitamin B12 deficiency, pregnancy, Addison disease, AIDS, malnutrition, Laugier-Hunziker syndrome and Peutz-Jeghers syndrome. Benign pigmented bands are a normal variant in darkly pigmented races and may be associated with certain drugs. Dr. Rich says these drugs include cancer chemotherapeutic drugs - such as bleomycin sulfate, cyclophosphamide, hydroxyurea, methotrexate - and other, more commonly-used drugs, such as minocycline, chloroquine, clomipramine and fluconazole, as well as fluoride, gold salts, phenytoin, psoralen, sulfonamides, timolol, thallium, zidovudine and others.
In addition, dermatologic causes for longitudinal melanonychias might include lichen planus, scleroderma, systemic lupus erythematosus (SLE), basal cell carcinoma, Bowen disease, lichen striatus, onychomatricoma, and nail infections such as Aspergillus, scopulariopsosis, candida and blastomycetes.
Nail plate dermoscopy may be helpful in sorting out pigmented bands. Irregular lines within the nail pigmentation on dermoscopy are more ominous than uniform lines.
“Matrical macules tend to be gray under dermoscopy, whereas melanomas and nevi are more often brown or black,” Dr. Rich says. “Just as with skin lesions, dermoscopy can provide clues and help guide the decision for biopsy, but should not be relied on for definitive diagnosis. End on dermoscopy of the free edge of the nail may be helpful in locating the pigment in the proximal or distal matrix.”
Types of biopsy
Longitudinal melanonychia requires matrix biopsy for diagnosis, which can be done by punch, lateral longitudinal excision or tangential excision.
“The simplest technique for matrix biopsy is a punch biopsy (through the plate or after removing the plate), which can be performed in the nail just as in the skin,” Dr. Rich says.
Rather than sampling a portion of the matrix lesion, most nail experts recommend removing the entire nidus of pigmentation in the matrix when possible.
“This helps minimize the likelihood of recurrent pigmented bands, which may result in a confusing clinical appearance after healing,” she says.
Tangential biopsy, originally performed by Eckart Haneke, M.D., provides a good alternative to punch or excisional biopsy of the matrix for pigmented lesions. “Most pigmented bands originate in the distal matrix, which helps us in several ways: the matrix is much thicker there, (and) the distal matrix forms the inferior part of the nail plate, so it is easiest to biopsy,” Dr. Rich says. “While technically more difficult (than the punch biopsy), a tangential matrix biopsy allows a larger piece of the nail matrix to be removed. However, because it is not full-thickness, risk of a pterygium or split nail dystrophy is low.”
The technique of tangential biopsy involves visualizing the focus of pigment in the matrix, which is scored around and removed tangentially, leaving portions of the thick nail matrix connective tissue behind.
“Except in very thick advanced melanomas where there is nail plate dystrophy, there is little risk of transecting the lesion. After the specimen is removed, the nail plate is replaced to cover the wound as a biologic dressing until the nail begins to regenerate,” Dr. Rich says.
Pathology will reveal if the section is malignant. “If the diagnosis is melanoma in situ, re-excision with adequate margins, which usually involves removal of the entire nail unit, is indicated. Only in advanced nail melanoma is amputation warranted,” she says.
Dr. Rich encourages dermatologists to help keep the management of nail disorders in the specialty of dermatology.
“It would be easy to let other specialties, such as podiatry and hand surgery, take care of patients’ nails, but they may not know as much about the epithelial structures, cutaneous oncology and nail physiology as dermatologist do,” she says. “Nails, like hair and mucous membranes, are really just extensions of skin.”