Clinical Review
2. WHEN PERFORMING A SHAVE BIOPSY, AVOID OBTAINING A SAMPLE THAT'S TOO SUPERFICIAL
The advantage of the shave biopsy is that it is minimally invasive and quick to perform. If kept small without compromising the amount of sample retrieved, the scars left by shave biopsies have the potential to blend well. The major disadvantage associated with the shave biopsy is that occasionally, if the shave is not deep enough, an insufficient amount of tissue is obtained. This can make it challenging to establish an accurate diagnosis.
Balancing the need to obtain adequate tissue with the desire to minimize scarring takes skill and experience. Taking a biopsy that is inadequate is a common occurrence. At times, the clinician’s clinical impression may be that a biopsy has obtained adequate tissue, when histologically only the superficial part of the skin surface has been sampled. This often is because of thickening of the superficial skin, whether as a manifestation of the anatomic site (eg, acral skin) or the disease process itself.
Unfortunately, this superficial skin often is nondiagnostic when unaccompanied by underlying epidermis and dermis. It is important to keep this in mind when you are obtaining a skin biopsy, especially when dealing with lesions that are very scaly or keratinized.
An equivocal biopsy wastes time, energy, and money, and it can negatively impact patient care.3 It can be difficult to balance practical aspects of the biopsy (ie, optimizing cosmetic outcomes, minimizing scarring and wound size) with the need to obtain sufficient tissue sampling (see Figure 1).
3. CHOOSE PUNCH OVER SHAVE BIOPSY FOR RASHES
In a punch biopsy, a disposable metal cylinder with a sharpened edge is used to “punch” out a piece of skin that can be examined under the microscope. Punch biopsy is the preferred technique for almost all inflammatory skin conditions (rashes) because the pathologist is able to examine both the superficial and deep portions of the dermis (see Figure 2).4
Pathologists use the pattern of inflammation, in conjunction with epidermal changes, to distinguish different types of inflammatory processes. For example, lichen planus is typically associated with superficial inflammation, while lupus is known to have prominent superficial and deep inflammation.
An inadequate punch biopsy sample can hinder histologic assessment of inflammatory skin disorders that involve both the superficial and deep portions of the dermis and can make arriving at a definitive diagnosis more challenging. The diameter of a punch cylinder ranges from 1 to 8 mm. Smaller punch biopsies often create diagnostic challenges because they provide so little sample. A punch biopsy size of 4 mm is commonly used for rashes.
An advantage of the punch biopsy is that patients are left with linear scars rather than the round, potentially dyspigmented (darker or lighter) scars that are often associated with shave biopsy. A well-sutured punch biopsy can be cosmetically elegant, particularly if closure is oriented along relaxed skin tension lines. For this reason, punch biopsies are well suited for cosmetically sensitive locations (eg, the face), although shave biopsies are also often performed on the face.
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