Mount the Menace! – Potassium hydroxide in superficial funga
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Potassium hydroxide (KOH) mount of clinical specimen is a common procedure in he dermatology for rapid detection of fungal elements in skin, hair, and nails. KOH is a cheap and readily available alkali. It is a strong base which softens, digests, and clears cellular and keratin debris but leaves fungal hyphae cell wall intact which is resistant to digestion by KOH, thus clearing the background and allows visualization of fungal elements under a microscope.

The procedure should be explained in detail to the patient and written informed consent should be taken before the procedure. The scraping should be collected from an active margin. The area should be cleaned with water or spirit before the procedure to remove dirt and/or any topical application
Blunt edge of a scalpel (15 No. blade) is used to collect the specimen onto a clean glass slide. The specimen can also be collected onto a presterilized black chart paper, black card, or cellophane tape if it has to be transported.

Once the scrapings have been placed on the glass slide, 1–2 drops of 10%–20% KOH for hair and skin samples and 20%–40% KOH for nail samples is added and gently covered with a glass slip. Excess fluid is removed with blotting paper. The slide is preheated before microscopic examination. Thicker skin or hair lesions may be left for an hour to allow adequate digestion of debris and intercellular cementing substances. Nail specimens may require a higher digestion time up to 24 h
The slide should be viewed under 10X to identify fungal elements and 40X to study the fungal morphology; Close the condenser partially for low intensity light to give a good contrast. If the light source is too intense, the contrast will not be adequate and the unstained fungal elements can be missed.

Dermatophytosis: Long, refractile, smooth, undulating, branching, and septate hyphal filaments with/without arthroconidiospores

Pityriasis versicolor: “Spaghetti and meatball” or “banana and grapes” which corresponds to the hyphae and spores, respectively

Tinea capitis: Ectothrix infection shows multiple spores lying in groups outside the hair shaft and is associated with destruction of the cuticle
In endothrix infections, the hair shaft will be broken and invaded by the mosaic of arthrospores or linear longitudinally arranged arthrospores within hair shaft.

Candidiasis: Pseudohyphae and budding yeast cells.

Instantaneous diagnosis of superficial fungal infections is warranted so that explicit treatment can be commenced without deferment; fungal culture takes a long time and hence not very practical. The KOH wet mount using microscopy is quick, inexpensive, and used routinely for diagnosis of superficial fungal infections, nevertheless, it requires skill to interpret.