A nail or nail bed biopsy is a direct means to diagnosis when routine clinical and laboratory methods fail to distinguish nail conditions. Nail bed biopsy can prevent misdiagnosis or delay in the diagnosis of potentially serious or disfiguring conditions such as subungual tumors. Occasionally, a biopsy can be therapeutic. Nail biopsy can provide rapid information that can guide therapy for inflammatory and infectious nail disorders, and it may prevent the unnecessary use of potentially hazardous, empirically applied medications.
Nail bed biopsy is easily performed in an office setting. The technique uses skills similar to those incorporated in skin biopsy of other sites. Despite good safety for the procedure, the potential for patient discomfort and permanent nail dystrophy discourages many providers from performing the technique. Proper patient selection and education is important to a successful outcome. Patients should be informed about the slow healing after a nail bed biopsy. Mean fingernail growth is 3 mm per month, and mean toenail growth is 1 mm per month.
A correct understanding of nail anatomy and physiology is important to a successful outcome. Some guiding principles for the performance of nail bed biopsy are listed in Table 32-1. The nail bed provides adherence of the nail plate, and biopsies of the nail bed usually heal without significant scarring. A 2- or 3-mm punch biopsy through the nail plate can provide accurate information about the nail bed. The nail matrix is the nail-forming tissue, and biopsies of the nail matrix can produce permanent dystrophy. Certain conditions are best diagnosed from a nail matrix biopsy, including unexplained longitudinal melanonychia, nail dystrophy involving the entire nail plate, and tumors of the nail matrix.
TABLE 32-1. PRINCIPLES GUIDING NAIL BED BIOPSY
When biopsying nail matrix, avoid transecting the matrix to prevent formation of a split nail deformity. The curvature of the lunula should be maintained, because this curvature is important to the proper contour of the nail. The superior surface of the nail plate is formed in the proximal matrix, and the underside of the nail is formed in the distal matrix. Biopsy should be performed in the distal matrix whenever possible. The thickness of the nail is determined by the length of the matrix. Tissue loss in the matrix can produce permanent, focal thinning of the nail plate.
Anatomy of the nail is depicted.
(1) Anatomy of the nail.
After a digital block, a 3-mm punch biopsy of the nail bed can be obtained. The technique of nail bed biopsy can be performed with or without nail plate avulsion. The punch instrument is passed vertically down to the periosteum, and the specimen is cut free with iris scissors. Monsel's solution can be used for hemostasis, and the site heals by secondary intention.
(2) After a digital block, a 3-mm punch biopsy specimen is obtained from the nail bed.
The double-punch technique for nail bed biopsy. A 5- or 6-mm punch is used to remove nail plate (Figure 3A). A 3-mm punch is then used in the center of the previously created window in the nail plate to obtain a specimen of the nail bed (Figure 3B).
(3) The double-punch technique for nail bed biopsy.
PITFALL: Do not damage the nail bed when using the larger punch to remove nail plate. Proceed slowly and carefully until the instrument just passes through the nail plate.
After a digital block, the proximal nail fold is separated from the nail plate using a Freer septum elevator (Figure 4A). Lateral incisions in the proximal nail fold (5 mm toward the distal interphalangeal joint) allow for the fold to be reflected (Figure 4B). The nail plate is gently separated from underlying tissues, and the plate is placed on the surgery tray (Figure 4C). A small, elliptical incision is created in the distal matrix, following the curvature of the lunula (Figure 4D). The defect is closed with interrupted 6-0 absorbable (polyglycan or Vicryl) suture. The nail plate must be repositioned beneath the proximal nail fold to prevent permanent dystrophy from scarring of the proximal nail fold onto the underlying matrix. A 5-0 nylon suture can be used to close the incisions in the proximal nail fold (Figure 4E). Some practitioners prefer to anchor the nail plate by suturing it to lateral tissues.
(4) Nail matrix biopsy.
PITFALL: The nail plate may be unintentionally discarded during the procedure. Other materials, such as petroleum-impregnated gauze or nonadherent or plastic dressings, can be used to separate the proximal nail fold from the nail matrix for 1 to 2 weeks after the procedure.
INSTRUMENT AND MATERIALS ORDERING
Disposable punch biopsy instruments and suture material can be obtained from surgical supply houses or from dermatology suppliers such as Delasco (http://www.delasco.com). The Freer septum elevator is available from sellers of surgical instruments.
Appendix A describes the instruments on a standard office surgery tray that can be used for nail biopsy. A suggested anesthesia tray that can be used for this procedure is listed in Appendix G. Skin preparation recommendations appear in Appendix H.
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