INTRODUCTION — A nail biopsy is performed to diagnose clinically ambiguous nail lesions or dystrophies or to remove tumors . Because of the propensity for scarring and inadequate sampling, nail biopsies are best performed by clinicians with appropriate training and experience. Prerequisites for a successful nail biopsy include a thorough understanding of nail anatomy, adequate anesthesia and hemostasis, and proper patient selection and preparation .
Before performing a nail biopsy, it is important to discuss with the patient the potential benefits and risks of the procedure and to address the patient's concerns about pain or scarring, including the possibility of permanent nail dystrophy.
This topic will discuss nail biopsy techniques according to anatomic site (eg, nail bed, nail fold, nail matrix). The anatomy of the nail, anesthesia and hemostasis techniques, patient selection, preoperative preparation, and postoperative care are discussed separately. (See "Principles and overview of nail surgery".)
CHOICE OF TECHNIQUE — The choice of the biopsy technique is usually based upon the site of the pathology within the nail and the risk of permanent scarring associated with the technique .
The nail plate usually needs to be partially or completely avulsed to allow access to the primary biopsy site regardless of biopsy technique . Partial nail plate avulsion is sufficient in many cases and avoids unnecessary trauma to the adjacent, uninvolved tissue (picture 1) . However, complete nail plate avulsion is occasionally necessary to achieve maximum exposure of the nail bed and matrix (see "Nail avulsion and chemical matricectomy", section on 'Nail avulsion'). If the origin of the lesion is not visible after nail plate avulsion, small releasing incisions in the proximal nail fold allow retraction of the nail fold with a skin hook for better visualization of the entire lesion.
After surgery, the nail plate should be put back in place whenever possible and held in place temporarily with sutures or tape . The repositioned nail plate will not permanently reattach but will effectively protect the wound and the nail bed for 3 to 12 postoperative weeks. When the avulsed nail plate is put back in place, openings can be made at the base, tip, or laterally to ensure drainage (picture 2A-B).
Tissue specimens, including the nail plate in some instances, should be placed in formalin in separate containers for proper histologic processing [2,5]. Histopathologic examination of the nail plate may provide clinically important information (eg, presence of melanocytic pigmentation, blood, or dematiaceous [pigment producing] fungi). Pathology requisition forms should specify if the tissue samples be sectioned longitudinally (ie, in the sagittal plane) rather than transversely, which is useful in certain tumors such as onychomatricoma (picture 3) . (See "Principles and overview of nail surgery", section on 'Managing the surgical specimen'.)
PREOPERATIVE PREPARATION — Preoperative preparation of the nail is discussed separately. (See "Principles and overview of nail surgery".)
NAIL BED BIOPSY
●Proximal subungual onychomycosis.
●Benign nail bed tumors, such as glomus tumor, fibroma, acral fibromyxoma, enchondroma.
●Inflammatory nail conditions, such as psoriasis and lichen planus.
●Subungual epidermal inclusions.
●Squamous cell carcinoma.
●Melanoma, specifically advanced and amelanotic melanoma. However, if a longitudinal, pigmented band is suspicious for melanoma, the biopsy must be taken from the nail matrix.
Techniques — Nail bed biopsy can be performed by punch biopsy or elliptical excision (figure 1). Any full thickness biopsy should extend to the depth of the periosteum . Although the nail bed generally heals without scarring, onycholysis may occasionally occur. To minimize the risk of scarring and subsequent onycholysis, nail bed biopsies should be oriented longitudinally, parallel with the natural longitudinal ridges.
Punch biopsy — Before performing a punch biopsy, the nail bed is usually exposed by partial or complete nail avulsion and inspected to select the optimal biopsy site. (See "Nail avulsion and chemical matricectomy", section on 'Nail avulsion'.)
A 3 mm punch is usually adequate to make most diagnoses. Following nail plate removal, the nail bed is assessed to determine the optimal site to achieve a pathologic diagnosis . The area to be biopsied is identified and scored with the punch instrument. Briefly removing the punch and examining the scored nail bed can confirm the exact location. The punch is then placed in exactly the same location and twisted with downward pressure until the instrument contacts the bone. Fine-tipped scissors (Gradle scissors) are inserted perpendicular to the nail bed and gently used to snip the base of the specimen at the level of periosteum. To avoid crush artifact, scissor tips can be used instead of forceps to gently lift and remove the specimen [2,4]. The 3 mm defect does not require repair.
Double punch technique — An alternative to partial or complete nail avulsion is the double punch technique. In this technique, the nail plate overlying the biopsy site is perforated with a larger size (eg, 5 to 6 mm) punch without injuring the underlying tissue. Soaking the digit in warm water for 10 minutes before the procedure can soften the plate and facilitate the procedure . The nail plate disc is then removed by using the tip of the scalpel and the nail bed is biopsied with a smaller size punch (eg, 3 mm), which can be removed through the larger hole in the nail plate .
Elliptical excision — An elliptical (fusiform) excision oriented in the longitudinal axis may be used if a larger sample of the nail bed is biopsied (figure 1). The elliptical excision requires full or partial nail avulsion. After excision, the nail bed defect can be repaired with 6.0 resorbable sutures.
NAIL FOLD BIOPSY — Indications for a nail fold biopsy include inflammatory conditions or focal tumors. Nail fold biopsy may be performed using punch, elliptical excision, or tangential (shave) excision techniques. These techniques are the same as those used for cutaneous surfaces . (See "Skin biopsy techniques".)
If an excision is necessary in a portion of the nail fold overlying the nail matrix, a Freer septum elevator may be inserted under the nail fold to protect the underlying nail matrix from inadvertent damage by the scalpel (picture 4) . Small nail fold defects heal well by secondary intention.
NAIL MATRIX BIOPSY
Indications — The single most important indication for a nail matrix biopsy is to exclude or confirm the diagnosis of subungual melanoma in a patient with longitudinal melanonychia [1,2,7]. In any case of melanonychia with a high preoperative likelihood of melanoma, it is important to perform a full-thickness biopsy. Tangential (shave) excision may not allow the accurate evaluation of Breslow thickness . (See "Tumor, node, metastasis (TNM) staging system and other prognostic factors in cutaneous melanoma", section on 'Tumor thickness'.)
Nail matrix biopsy also may be indicated in other conditions if the diagnosis is uncertain.
General principles — The nail matrix biopsy is associated with a greater risk of scarring than other locations within the nail unit. Full-thickness nail matrix biopsies larger than 3 mm can be sutured to achieve an optimal cosmetic result [5,8].
When possible, distal matrix biopsies are preferred to proximal matrix biopsies. Since the distal matrix forms the ventral portion of the nail plate and the proximal matrix forms the dorsal portion (figure 2), the sequelae of distal matrix biopsy (thinned ridges) manifest on the undersurface of the nail [1,7,9-11]. Thinned ridges of the dorsal surface of the nail plate are easily traumatized and may catch on items such as clothing, causing considerable discomfort to the patient (picture 5) .
Full thickness techniques
Punch biopsy — The punch biopsy is generally reserved for sampling longitudinal melanonychia <2.5 to 3 mm in width that originates in the distal matrix [2,5]. A punch biopsy should be taken at the origin of the band and should extend to the depth of the periosteum (picture 6) [2,5]. It is preferable to remove the entire nidus of pigmentation in the matrix. Sampling a portion of the lesion may result in ambiguous pigmentation after healing.
Punch biopsy is generally not recommended for evaluating pigmented lesions ≥3 mm in width because peripheral pigmentation may not be adequately sampled to rule out malignancy. Multiple punch biopsies are also not recommended because they are associated with an increased risk of permanent nail dystrophy .
Longitudinal elliptical excision — A longitudinal elliptical excision of the proximal matrix may be performed as an alternative to punch biopsy to excise lesions causing longitudinal melanonychia <3 mm in width . Closure of the surgical defect is performed with 6.0 absorbable suture material.
Lateral longitudinal excision — The lateral longitudinal excision is best suited for biopsying longitudinal melanonychia located in the lateral one-third of the nail. Since this technique samples all components of the nail unit, it is also useful for the diagnosis of inflammatory conditions in which the nail bed, nail matrix, nail plate, nail folds, and hyponychium are concurrently involved [2,5].
A number 10 or 15 scalpel blade can be used to cut through the skin and soft tissue down to the periosteum, proximally from a point halfway between the cuticle and the distal interphalangeal skin fold, 1 to 2 mm medial to the pigmented band, through the nail plate, and 3 to 4 mm past the hyponychium onto the digital tip (picture 7) .
The blade can then be reinserted laterally from the previous starting point and the cut made so that the entire matrix horn is included. The cut then courses into the nail sulcus and curves medially at the hyponychium and beyond to meet the end point of the first incision. In this way, the incision is nearly elliptical (picture 7). The tissue specimen is then carefully removed and placed in formalin.
Lateral matrix pocket debridement with a small curette or a hemostat tip covered with gauze should be performed before tissue repair to prevent small matrix remnants from being left behind and causing postoperative cysts, spicules, and/or pain. Sutures can be placed to realign the proximal nail fold to the lateral nail fold and should remain in place for 10 to 14 days.
Transverse matrix excision — The transverse nail matrix biopsy may be performed to excise matrix lesions that are >3 mm in width. To minimize any potential scarring, the lesion is removed by excising an elliptical or crescent-shaped wedge of tissue with the distal margin matching the shape of the lunula (figure 1) [1,2,7].
Partial thickness techniques
Tangential (shave) excision — The tangential (shave) excision is ideal for sampling longitudinal melanonychia that has a low preoperative suspicion of melanoma, is >3 mm in width, and located in the mid-nail plate (picture 8) . The tangential shave is also the preferred technique for sampling longitudinal melanonychia of any width originating in the nail matrix, when the suspicion of melanoma is low [2,5,12]. The tangential technique is less invasive than a transversely oriented matrix excision and is associated with minimal long-term dystrophy despite the larger area of the excised matrix tissue, due to the remaining CD10-positive mesenchymal cells in the onychodermis . This technique can be both diagnostic and therapeutic and works well for nail matrix and nail bed lesions. Studies have shown that the risk of transection of the lesion with this biopsy method is low with skillful removal of the entire pigmented lesion in the nail matrix . Recurrence of pigmentation is common after tangential excision of pigmented lesions in the nail matrix and may require re-excision. In one study, recurrence was observed 8 to 12 months postsurgery in 16 of 23 patients with longitudinal melanonychia treated with tangential excision .
Releasing incisions are made at the junction of the proximal and lateral nail folds; the proximal nail fold and cuticle are then carefully reflected proximally to expose the underlying matrix . The nail plate is completely or partially avulsed using an English anvil action nail splitter or similar instrument. (See "Nail avulsion and chemical matricectomy", section on 'Nail avulsion'.)
Using a number 15 blade, the pigmented lesion is sampled in its entirety with 1 to 2 mm margins using a tangential excision (shave biopsy) technique (picture 8). To facilitate tissue processing and prevent tissue curling, the specimen can be placed on a paper or cardboard template or in a cassette before placing it in a formalin jar (picture 9). Repair of the remaining defect is straightforward. Absorbable sutures are generally used to approximate defects 3 mm or larger. The nail plate can be put back in place and secured with tape or sutures following the procedure to protect the nail bed.
Full thickness excision of the entire nail unit — En bloc excision of the nail unit is sometimes necessary for malignant nail lesions, such as in situ and minimally invasive melanoma and squamous cell carcinoma in situ. This technique is used as an alternative to amputation to preserve function of the digit in patients with minimally invasive melanoma (Breslow thickness <0.5 mm) and occasionally extensive squamous cell carcinoma in situ when Mohs surgery is not an option . En bloc excision involves full surgical excision of the entire nail unit, including the nail bed down to periosteum, and the full nail matrix, including the lateral horns of the matrix. The wound is usually allowed to heal by secondary intention, although a skin graft is sometimes indicated. This technique allows the entire nail unit to be submitted to pathology for careful margin evaluation.
●Choice of technique − The choice of the nail biopsy technique is usually based upon evaluation of the site involved in the disease process within the nail unit and the risk of permanent scarring associated with the technique. Regardless of the technique used, the nail plate needs to be partially or completely avulsed or punched to allow access to the primary biopsy site. (See 'Choice of technique' above.)
●Indications for nail bed biopsy − Nail bed biopsy is useful for diagnosing infectious, inflammatory, and neoplastic disorders, including onychomycosis, psoriasis, lichen planus, squamous cell carcinoma or melanoma. Nail bed biopsy can be performed by punch, elliptical excision, or tangential (shave) excision (figure 1). (See 'Nail bed biopsy' above.)
●Indications for nail fold biopsy − Nail fold biopsy is performed by punch, elliptical excision, or tangential (shave) excision. Indications for a nail fold biopsy include inflammatory conditions or focal tumors. (See 'Nail fold biopsy' above.)
●Indications for nail matrix biopsy − The single most important indication for a nail matrix biopsy is to exclude or confirm the diagnosis of subungual melanoma in a patient with longitudinal melanonychia. Nail matrix biopsies may be performed by punch, longitudinal or transverse matrix elliptical excision, or shave excision. (See 'Nail matrix biopsy' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Julie A Jefferson, MD, who contributed to an earlier version of this topic review.
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