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Year : 2020  |  Volume : 21  |  Issue : 4  |  Page : 343-346

Mount the Menace! – Potassium hydroxide in superficial fungal infections

Department of Dermatology, Venereology and Leprosy, Dr. DY Patil Medical College and Hospital, Navi Mumbai, Maharashtra, India

Date of Submission16-Aug-2020
Date of Decision05-Oct-2020
Date of Acceptance08-Oct-2020
Date of Web Publication30-Sep-2020

Correspondence Address:
Dr. Saloni Bhatia
Kishan's Abode, 12th Floor, 14th Road, Bandra, West Mumbai - 400 050, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2319-7250.296851

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How to cite this article:
Gautam M, Bhatia S. Mount the Menace! – Potassium hydroxide in superficial fungal infections. Indian J Paediatr Dermatol 2020;21:343-6

How to cite this URL:
Gautam M, Bhatia S. Mount the Menace! – Potassium hydroxide in superficial fungal infections. Indian J Paediatr Dermatol [serial online] 2020 [cited 2020 Oct 19];21:343-6. Available from: https://www.ijpd.in/text.asp?2020/21/4/343/296851

  What Is Potassium Hydroxide Mount? Top

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.

  Discuss the Historical Aspects of Koh Mount? Top

KOH mount in superficial fungal infections has been used for more than a hundred years. However there is no historical consensus on the inception of this procedure. and the pioneer of the original KOH preparation still remains a mystery.

  What Are the Prerequisites for This Procedure? Top

Glass slide, cover slip, scalpel, 10% KOH, Bunsen's flame, and microscope.

  How Is 10% Potassium Hydroxide Prepared? Top

10% KOH solution is made by adding 10g of KOH crystals to 50 ml of distilled water. Stir until the crystals completely dissolve. Add 10 ml of glycerol (to prevent drying). Add remaining distilled water to make the volume 100ml. It is corrosive and should be handled with care and stored at room temperature.

  What Are the Different Concentrations of Potassium Hydroxide Which Can Be Used for This Procedure? Top

Routinely, 10% or 20% KOH is used for skin and hair specimens. However, 20%-40% KOH is used for nails as well as for thick hyperkeratotic specimen.

  What Is the Ideal Digestion Time or Clearing Time? Top

It generally takes 10-15 minutes for digestion of cellular and keratin debris. Thick hyperkeratotic sample may take 30 minutes to an hour for digestion. Nail and hair specimens may require 24-48 h for clearing.

  How Can You Reduce the Clearing Time for Hair and Nail Specimens? Top

  • By using higher concentration of KOH such as 20% or 40%
  • Preheating the slide before microscopic examination.
  • Addition of 40% Dimethyl Sulfoxide (DMSO) to 10% KOH in equal proportion causes rapid digestion of keratin. This allows immediate examination of the specimen without the need for heating the slide.

  What Are the Different Specimens That Can Be Collected for Potassium Hydroxide Mount? Top

  • Cutaneous dermatophyte infections

    Lesions suspected to have underlying fungal pathology are identified. The advancing border is the ideal site which yields better results due to higher fungal activity. In majority of tinea plaques, there is an advancing rim of erythematous papules and vesicles, which are the ideal sites for scrapings. Preferably, samples should be taken from multiple sites to give better results. The skin scrapings can be collected using the edge of a clean glass slide or using the blunt end of a surgical blade. Collect adequate sample to get a higher yield of fungal elements. Inadequate sample may give false negative results.
  • Tinea capitis or tinea barbae

    Plucked hair, epilated hair, hair stubs, and matted hair crusts are valuable samples. Always include skin scrapings from the surrounding infected scalp in your hair mount.

    Lusterless hair in proximity to the surface should be plucked along with its root with the help of sterile epilation forceps.

    Woods lamp can be used to identify infected hair which gives yellow green fluorescence in case of Microsporum species and bluish green in case of  Trichophyton schoenleinii More Details. To assist clearing the hair shaft length should not exceed 5mm.
  • Onychomycosis

    • Nail clippings, avulsed nails, subungual debris, undersurface of the nail plates are samples that can be collected for onychomycosis. To assist clearing the nail clippings should not be more than 2-3mm thick.
    • Clippings should be as proximal as possible.

  • Tinea versicolor

    Scaly hypopigmented or hyperpigmented lesions are identified, scratching the lesion causes accentuation of the scales (Besnier's sign), and the scaly edges often yield good results.
  • Candidiasis

    Samples are taken depending on the site of infection, e.g., curdy white discharge in the oral cavity, vagina, glans penis, satellite pustules of cutaneous lesion, diaper area, web spaces, and nail clippings.

  Explain the Procedure of Potassium Hydroxide Mount in Detail? Top

  • 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 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 [1]
  • Quantity and quality of the material examined are critical for a laboratory to provide optimal results
  • 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 [2]
  • 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.

  What Precautions/care Should Be Taken While Performing a Potassium Hydroxide Mount? Top

  • Any medicament applied/cloth fibers should be washed off with distilled water before collecting the sample
  • Excessive scales collected cause heaping up of dissolved keratin which can interfere with the results. This can be prevented by avoiding mounting up of scales when they are being placed on the glass slide
  • Excess heating of the slide should be avoided to prevent KOH crystal formation.

  What Are the Findings That You Look for in a Potassium Hydroxide Mount? Top

  • Dermatophytosis: Long, refractile, smooth, undulating, branching, and septate hyphal filaments with/without arthroconidiospores [3] [Figure 1]
  • Pityriasis versicolor: “Spaghetti and meatball” or “banana and grapes” which corresponds to the hyphae and spores, respectively [Figure 2]
  • Tinea capitis
  • Ectothrix infection shows multiple spores lying in groups outside the hair shaft and is associated with destruction of the cuticle [Figure 3].
  • 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.
Figure 1: 10% Potassium hydroxide mount (×10): Dermatophytes – long refractile, branching, and septate hyphae

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Figure 2: 10% Potassium hydroxide mount (×10): Spaghetti and meatball appearance of pityriasis versicolor

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Figure 3: 10% Potassium hydroxide with Chicago sky blue stain showing spores and hyphae around hair shaft in ectothrix

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  What Are the Modifications of Potassium Hydroxide Mount? Top

Conventional KOH mount does not provide color contrast and hence visualization of fungal elements is difficult for the inexperienced. Certain modifications can be done for better visualization of fungal elements as follows:

  1. KOH with Parker blue black ink: It is not denatured with KOH and stains the fungal elements bluish violet
  2. Combination of 1% Chicago sky blue (CSB) with KOH: CSB, used as a contrast stain, has shown potential as a rapid and reliable method in the diagnosis of dermatomycoses, making interpretation very affordable and easy. KOH is used as the clearing agent [4] [Figure 4].

    Dermatophytes can be visualized more easily, increasing the sensitivity and specificity of KOH.
  3. Other stains: Chlorazol black E has affinity for chitin and stains fungal cell wall blackish blue. Addition of 1% eosin to Parker's ink in 2:1 proportion will stain the fungal elements blue (due to Parker's ink) against a pink background (due to eosin). Calcofluor white is a fluorescent stain for rapid detection of fungi. One drop of this stain along with one drop of 10% KOH solution can be added to the specimen. The fungal elements show a brilliant apple green fluorescence under UV light.
Figure 4: Chicago sky blue stain of skin scrapings of dermatophytosis (×10) showing blue branching and septate fungal hyphae

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  Discuss the Cellophane Tape Method of Koh Hydroxide Mount Top

It is a modification of the conventional KOH mount where a transparent cellophane tape is applied over the affected site, pressed firmly and removed. The tape is stuck on a sterile glass slide over which a few drops of 10% KOH solution are added. Cellophane tape method is less time consuming and easy to transport. Good amount of sample can be collected using cellophane tape especially when the scales are scanty. It reduces the chances of drying of the mount due to its occlusive property. It can be used as an alternative in children for the collection of specimens rather than scraping with a scalpel blade.[1]

  Potassium Hydroxide Mount Versus Fungal Culture: What Are the Advantages and Disadvantages? Top

The comparison between KOH and fungal culture is shown in [Table 1].
Table 1: Comparison between potassium hydroxide mount and fungal culture

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  What Is the Sensitivity and Specificity of Potassium Hydroxide Mount in Various Conditions? Top

The sensitivity and specificity of KOH in various conditions are mentioned in [Table 2].[7]
Table 2: The sensitivity and specificity of potassium hydroxide mount in various conditions

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  What Are the Other Indications of Potassium Hydroxide Mount? Top

  1. Piedra: KOH mount of crushed nodules on hair shaft show septate hyphae within concretions. The hyphae are densely packed in black piedra and loosely arranged in white piedra
  2. Tinea nigra: Brown branching septate hyphae and budding cells of Hortaea werneckii
  3. In bacterial vaginosis, addition of few KOH drops to vaginal discharge gives fishy odor. On light microscopy, “clue cells” will be seen
  4. Skin mount to demonstrate Sarcoptes scabiei mite and Demodex folliculorum mite
  5. Blue neck syndrome to demonstrate nematode larvae from skin scrapings
  6. KOH mount study on the sputum samples can help identify Aspergillus infection by the presence of V-shaped branching and septate hyphae
  7. Mucormycosis aseptate hyphae will be seen.

  What Are the Advantages of Potassium Hydroxide? Top

  • Economical, swift, and easy-to-perform test
  • Minimally invasive procedure
  • Requires minimum infrastructure
  • KOH is a reliable, outpatient procedure which yields quick results. Fungal culture, although a good confirmatory test for identifying fungus, is more expensive and takes minimum 3 weeks before the results can be obtained
  • KOH can be used as a primary screening tool for the detection of fungal elements from hair, skin, nails, and sputum samples.

  What Are the Disadvantages of Potassium Hydroxide? Top

  • Artifacts such as clothing fibers and mosaic fungus may interfere with the results. Mosaic fungus is the irregular, branching network which follows the contours of the epidermal skin cells. It can be easily mistaken for fungal hyphae. However fungal hyphae are refractile whereas mosaic fungus is non-refractile. Also the hyphae will cross the borders of epidermal skin cells but artifacts will not
  • Low sensitivity when hyphae are sparse. A negative test does not rule out fungal infection
  • Though rapid, the KOH wet mount lacks a color contrast and necessitates considerable expertise for interpretation
  • There have been concerns regarding the dissemination of infection to adjoining areas during the test
  • Unable to identify the species of the fungus
  • As it lacks specificity, it is not useful in monitoring response to treatment.

  Summary Top

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.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Thirumurthy M, Sethuraman G, Srinivas CR. KOH mount for superficial fungal infections using cellophane tape: Comparison with standard technique. Indian J Dermatol Venereol Leprol 2002;68:136.  Back to cited text no. 1
[PUBMED]  [Full text]  
Kurade SM, Amladi SA, Miskeen AK. Skin scraping and a potassium hydroxide mount. Indian J Dermatol Venereol Leprol 2006;72:238-41.  Back to cited text no. 2
[PUBMED]  [Full text]  
Surendran K, Bhat RM, Boloor R, Nandakishore B, Sukumar D. A clinical and mycological study of dermatophytic infections. Indian J Dermatol 2014;59:262-7.  Back to cited text no. 3
[PUBMED]  [Full text]  
Baddireddy K, Poojary S. A novel contrast stain for the rapid diagnosis of dermatophytoses: A cross-sectional comparative study of Chicago sky blue 6B stain, potassium hydroxide mount and culture. Indian J Dermatol 2019;64:311-4.  Back to cited text no. 4
[PUBMED]  [Full text]  
Begari V, Pathakumari P, Takalkar AA. Comparative evaluation of KOH mount, fungal culture and PAS staining in onychomycosis. Int J Res Dermatol 2019;5:554-8.  Back to cited text no. 5
Hu L, Zhou P, Zhao W, Hua H, Yan Z. Fluorescence staining vs. routine KOH smear for rapid diagnosis of oral candidiasis-A diagnostic test. Oral Dis 2020;26:941-7.  Back to cited text no. 6
Lodha N, Poojary SA. A novel contrast stain for the rapid diagnosis of pityriasis versicolor: A comparison of Chicago sky blue 6B stain, potassium hydroxide mount and culture. Indian J Dermatol 2015;60:340-4.  Back to cited text no. 7
[PUBMED]  [Full text]  


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2]


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