Fungal elements (hyphae and/or spores) can be found in affected tissues taken from patients with supemcial fungal diseases such as candidiasis, pityriasis (tinea) versicolor, and dermatophyte infections of the skin, hair, and nails. The potassium hydroxide (KOH) preparations that identify these hyphae are both sensitive and specific. Scale, pustules, blister roofs, and clippings taken from hair and nails may be examined with this technique. Most often, KOH examination will be carried out during the evaluation of scaling disorders. In such instances, scrapings are obtained after the affected skin has been moistened with an alcohol sponge or with tap water. Then, before the lesion dries, the sharp edge of a no. 15 scalpel blade held perpendicular to the skin is scraped across the surface. The moistened scale that sticks to the edge of the blade is then transferred to a microscope slide. One drop of a 10% to 20% solution of potassium hydroxide (KOH) is then placed over the material on the slide. A coverslip is added. If the scale is fine and has been spread thinly on the slide, the preparation can be examined immediately. If the scale is thick or if fragments of hair or nails are to be examined, gentle heating of the slide may be necessary in order to get a layer of cells thin enough to examine.
In examining the slide the condenser is racked to its lowest position, and the intensity of the light source is reduced. These two maneuvers increase the contrast between the fungal hyphae and the underlying epithelial cells. The medium-power objective is used for scanning the field, and the high-power objective is used to confirm the presence of suspected hyphae.
In pityriasis (tinea) versicolor, fungal hyphae are short, stubby, and vaguely” Y” shaped . Small round spores are numerous and are collected in clusters around the hyphae. The terms “grapes on a branch” and “spaghetti and meatballs” are often used to describe these hyphae and spores.
In dermatophyte and Candida infections the hyphae are thinner and longer. Few if any spores are present. Most observers cannot easily separate the pseudohyphae of Candida infections from the true hyphae of dermatophyte infections, and a decision as to which of the two infections is present usually depends on the clinical presentation or subsequent culture.
Artifacts are commonly present in KOH preparations and may be confused with hyphae. Cotton threads are thicker and lack parallel sides and branching. Hairs have parallel sides, but they too lack branching. The edges of epithelial cells sometimes overlap and appear to form a continuous, branching line. In such a situation, compression of the coverslip against the slide will cause the cells to change position and separate, thus breaking up the erroneous hyphae-like appearance of the cell outlines.
The unequivocal presence of hyphae on a KOH preparation identifies the disease in question as being of fungal origin. Therapy can be initiated on the basis of this finding without waiting for the report of a fungal culture.
Tags:dermatophyte infections, hyphae KOH
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