Key Terms
Saucerization biopsy
Tinea corporis
Equipment Needed
This chapter, on diagnostic techniques, not only discusses how to perform the procedures, but also lists the type of equipment needed to perform these techniques.
There are numerous medical supply houses that supply surgical and diagnostic equipment that can equip an emergency room or an office adequately. Although we do not have any financial interest in this company, we can recommend Delasco, which has a complete line of equipment directed for dermatologists, including anything mentioned in this text.
Core cutaneous surgical equipment
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Scalpel, no. 14 blade
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Scalpel handle
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3-mm disposable punch
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4-mm disposable punch
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Curved iris scissors
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Suture scissors
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Tissue forceps (e.g., 4-inch iris with teeth)
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Needle holders
Optional cutaneous surgical equipment
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2-mm disposable punch
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5-mm disposable punch
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6-mm disposable punch
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8-mm disposable punch
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Flexible, double-edged razor blades
Core diagnostic equipment
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Microscope
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Mineral oil
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Mycologic media—Sabouraud agar (plates, tubes or slants)
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10% to 20% potassium hydroxide (KOH) solution, with or without dimethyl sulfoxide (DMSO)
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Glass slides and coverslips
Optional diagnostic equipment
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Antifungal stains (as alternatives to KOH)
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Chlorazol black fungal stain
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PMS fungal stain
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Swartz Lamkins fungal stain
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Methylene blue Triton X (for Malassezia yeast)
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Dermatophyte test medium (DTM)
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Tzanck stains
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PMS Tzanck stain
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Wright-Giemsa stain
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Wood light (Wood lamp)
Wood Light
Introduction
The Wood light or Wood lamp emits long-wave UV light (black light) that is filtered by a Wood filter (barium silicate and nickel oxide) that only allows a band of UV light between 320 and 400 nm (peak, 365 nm) to be emitted.
Applications
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Diagnosis of fluorescent species of tinea capitis
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Diagnosis of erythrasma
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Examination of porphyrins in urine in porphyrias, such as porphyria cutanea tarda ( Fig. 2.1 )
Fig. 2.1
Wood light examination of urine demonstrating coral red fluorescence in a patient with porphyria cutanea tarda. Fluorescence can be accentuated by adding dilute hydrochloric acid. Left, Positive. Right, Negative.
(From the Fitzsimons Army Medical Center Collection, Aurora, CO.)
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Examination for Propionibacterium acnes in patients with acne vulgaris ( Fig. 2.2 )
Fig. 2.2
Wood light examination of a patient’s nose demonstrating coral red porphyrins produced by Propionibacterium acnes . Because this patient is under treatment for acne, this finding indicates that the patient is not taking the antibiotic or the organism is resistant to the antibiotic.
(From the Fitzsimons Army Medical Center Collection, Aurora, CO.)
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Demonstration of hypopigmentation and depigmentation in light-skinned individuals
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Pseudomonas aeruginosa infection (e.g., burns, ulcers)
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Detection of tetracycline deposition in children’s teeth
Supplies
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Wood light (Wood lamp)
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Wood lights are available as small, portable, battery-powered units or as larger units with a cord
Technique
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Completely darken the examination room and allow your eye to accommodate.
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Turn on the lamp and allow it to warm up for 30 to 60 seconds.
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Hold the lamp approximately 4 to 6 inches from examination site.
Interpretation
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A positive examination result for tinea capitis consists of yellow-green or blue-green fluorescence of the broken hair shafts caused by the production of a compound called pteridine. Care must be taken not to confuse this with fibers and lint from clothing that may fluoresce a white color (due to optical brightening agents) or scale mixed with sebum that may demonstrate a dull yellow color.
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A positive test for erythrasma demonstrates a coral red fluorescence confined to the areas of infection. The color is due to a water-soluble porphyrin (coproporphyrin III) produced by the bacteria Corynebacterium minutissimum . The porphyrins are water-soluble and, if the patient has recently bathed, the test will be negative because the fluorescent porphyrins will be washed out.
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In acne vulgaris, untreated patients will demonstrate follicular coral red fluorescence. In treated patients, if fluorescence is still present, the patient is not using the medication or the Propionibacterium acnes is now resistant to the antibiotics.
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A positive test for urinary porphyrins is the demonstration of coral red fluorescence in the urine. If the amount of uroporphyrins is low, only the meniscus will demonstrate the color, but if the quantitative porphyrin level is high, the entire sample will demonstrate coral red fluorescence.
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Pseudomonas infections show a greenish fluorescence due to the pigment pyoverdin.
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Hypopigmented or depigmented skin in fair-skinned individuals is accentuated with a Wood light.
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False-negative results may occur in acne vulgaris and erythrasma if the patient has recently bathed.
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False-positive fluorescent substances include some cosmetics, deodorants, soaps, lint, and petrolatum.
Comments
The Wood light has severe limitations in the diagnosis of tinea capitis because most infections in the United States are due to nonfluorescent species, especially Trichophyton tonsurans . The only species that is commonly fluorescent in the United States is Microsporum canis, which only accounts for about 5% to 10% of cases.
Potassium Hydroxide Preparation
Applications
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Diagnosis of dermatophytes and yeast infections of the skin and mucous membranes
Supplies
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Microscope glass slide
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Coverslip (any size)
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No. 14 or 15 scalpel blade
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KOH, 10% to 20% concentration ( Fig. 2.3 ). Variants include the following:
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KOH, 10% to 20%, with DMSO
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KOH, 10%, with DMSO and chlorazol black
Fig. 2.3
Top row, Fungal KOH (with and without DMSO). Bottom row, Four different types of fungal stains. Far right, Special glass slides with adhesive tape used for the diagnosis of tinea versicolor.
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Access to a microscope
Technique
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For tinea corporis, the best samples are from annular edges with scale.
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Wet the area with an alcohol pad or, if in a sensitive area, with water.
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Gently scrape the site (you should not draw blood) and gather as much scale on the edge of the scalpel blade as possible. It is best to do this on more than one site to ensure that you have enough material ( Fig. 2.4 ).
Fig. 2.4
After wetting the skin of a patient with suspected tinea pedis, the area is gently scraped with a no. 15 scalpel blade. Because the stratum corneum (scale) is the material of interest, the procedure should not draw blood.
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Transfer the material on the edge of the scalp to the glass slide and spread it across the slide.
Warning!
Be very careful not to get the KOH on the microscope objectives because KOH can permanently etch the lens. Obviously, anything that will etch glass should not come into contact with the skin of patients, the staff, or yourself.
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Apply one or two drops of KOH to the slide ( Fig. 2.5 ) and coverslip.
Fig. 2.5
A single drop of KOH is placed on the scale and then cover-slipped. Note that the physician is wearing gloves—remember that KOH is toxic to the skin.
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If the coverslip is not even, gently press with your finger.
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Blot any excess KOH at the edges of the coverslip.
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If DMSO is used, wait for 1 minute to examine.
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If DMSO is not used, gently heat (do not boil) the glass slide to enhance clearing of the keratinocytes ( Fig. 2.6 ).
Fig. 2.6
After being cover-slipped, the KOH preparation is gently heated over a flame. If the KOH contains DMSO, this step can often be omitted. After heating, the slide is ready to be examined under the microscope.
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The hyphae are easier to visualize if the condenser is dropped. The amount that it needs to be dropped is variable and depends on the amount of light used and thickness of the specimen.
Interpretation
