c. Skin Biopsies. Skin biopsies are used to diagnose skin conditions that
cannot be identified by their appearance or skin conditions that do not respond to
treatment. Without a biopsy, it is often impossible to determine whether a skin problem-
particularly a mole or other skin lesion that has changed in size or color, or sore that has
not healed--is cancerous. A skin biopsy is also used to diagnose some bacterial and
fungal skin infections and a number of other skin conditions.
(1) Types of skin biopsies. There are three kinds of skin biopsy: a punch
biopsy, a shave biopsy, and an excisional biopsy. In a punch biopsy, a small cylinder of
skin, sometimes only a part of the problem area, is removed with a skin punch. In a
shave biopsy, the outer portion of the problem area is removed. In an excisional biopsy,
the entire problem area of skin (for example, a skin growth) is removed. Results of
these biopsies are usually available in seven to ten days. The results of the biopsy will
indicate either a benign (noncancerous) or malignant (cancerous) skin condition.
Common noncancerous or benign growths include cysts, warts, moles, keloids,
dermatofibromas, and neurofibromas. Skin cancers are the most common cancers in
humans. Three quarters of skin cancer cases are basal-cell carcinoma, a
nonthreatening skin cancer found most frequently on the head and neck. Biopsy
specimens can also detect bacterial and fungal infections as well as inflammatory skin
diseases.
(2)
The procedure.
(a) Punch biopsy. In a punch biopsy, a local anesthetic is injected and
the skin around the area to be sampled is pulled taut. A hollow instrument (the punch)
is inserted into the skin. The instrument is rotated and circles a "plug" of skin and some
underlying fat. The instrument (the punch) is removed, and a forceps or needle is used
to remove the plug (the sample). If a large specimen has been removed, the skin may
be closed with one or two stitches. If a small specimen was taken, pressure on the area
will often control the bleeding.
(b) Shave biopsy. After a local anesthetic is injected, a doctor uses a
sharp scalpel to cut the growth off even with the skin. Bleeding is controlled with
pressure.
(c) Excisional biopsy. A local anesthetic is injected. The entire lump,
spot, or sore is cut out with a scalpel. Usually, the incision is closed with stitches and
bleeding is controlled with pressure. If the biopsy is large, a skin graft may be used to
cover it.
d. Patch and Intradermal Tests.
(1) Allergy testing. Allergies result from a malfunction of the body's immune
system, a system that usually protects us from foreign substances. For a person with
allergies, his immune system overreacts to normally harmless foreign substances such
as pollens, dusts, danders, or foods. The overreaction can cause sneezing, wheezing,
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