2-6

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2-6. SPECIALIZED PROCEDURES

a. Bacterial Smears and Cultures. Identifying the bacteria in skin lesions is very important in determining the cause of the skin lesion and whether the lesion is primary or secondary. Two methods can be used to identify bacteria: Gram's stain and a blood culture. In the Gram's stain method, microorganisms are stained with crystal violet and further treated with other chemicals. The end result is that these microorganisms can be identified as gram- positive or gram-negative. Appropriate treatment can then be determined. Gram's stain is a rapid method of examining a lesion sample for the number and type of bacteria as well as for the character of the inflammatory matter coming from the lesion. Often the Gram stain provides the first clue as to the specific cause of the infection causing the skin lesion(s). If skin lesions are thought to be part of a generalized infection, blood cultures should be taken. Care must be taken to obtain the blood culture from an area in which there are not skin lesions. When gram-stain examination and cultures have been performed, a reliable diagnosis of the cause of the skin lesion can be made and treatment prescribed.

b. Fungal Smears and Cultures. There is a tendency in dealing with skin problems where fungus is concerned to minimize the necessity for cultures to confirm the diagnosis. The general impression is that modern antibiotics and antifungal agents can take care of the fungus problem. However, many skin diseases look very much alike so that a clinical diagnosis often needs to be supported by a laboratory diagnosis--a culture. The location of the fungus will determine the type of clinical specimen to be collected: infected hairs for a fungus attacking hair and nail scrapings for a fungus attacking nails. Collecting the appropriate specimen, proper handling and processing, and correct culturing techniques are skills which are generally acquired through practice.

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, watery eyes, itching, rash, and sometimes even life-threatening anaphylactic shock. Allergy testing is performed to find out what exactly an individual is allergic to. Skin tests are most often done to identify the cause of sneezing, runny nose, and nasal congestion of hay fever or the wheezing of asthma. Patch tests are done to help diagnose unexplained rashes. Allergy tests are usually done by a doctor or technician. The three types of allergy tests are the scratch test, the intradermal test, and the Patch test.

(a) The scratch test. This test is used often because the reaction it can produce is less severe in a person who is highly allergic to substances. In this test, very small amounts of dilute solutions of different suspected allergens (grasses, weeds, trees, molds, dusts, and foods) are placed on the patient's arm or back. The skin beneath the sample is lightly scratched with a sterile pin. After twenty

to thirty minutes, the scratched areas are examined for a reaction such as

redness, swelling, and blistering. The entire test usually takes about thirty to forty minutes and may be repeated later.

 

(b) The intradermal test. In this test, small amounts of various suspected allergens are injected into the skin on the patient's arms or back. After twenty to thirty minutes, the injection sites are evaluated for reactions.

 

(c) The Patch test. Diluted samples of suspected allergens are placed on small pieces of filter paper and taped to the skin on the patient's back. The patches are left in place for twenty-four to forty-eight hours. During this period, the patient should not bathe or engage in any activity that might cause him to sweat and loosen the patches. After the required number of hours, the patches are removed, and any skin reactions under the patches are examined.

(2) Tuberculosis tests. The purpose of a tuberculin skin test is to determine whether the person was ever infected by the bacterium that causes tuberculosis. The individual's immune system will produce swelling at the injection site one to two days after the skin test if that person has been infected with tuberculosis or vaccinated against tuberculosis any time in the past. Two commonly used skin tests are the tine test and the Mantoux test. The tine test uses dried, old tuberculin (OT) on several metal tines embedded in a round plastic head. The tines are pressed against the person's skin, and the antigen enters the dermis layer of skin. This method is convenient and safe for mass surveys. The most accurate method of tuberculin testing is the Mantoux test, which requires injection of antigen into the epidermal skin layer.

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