Dermatophytosis laboratory findings
Overview
Laboratory findings consistent with the diagnosis of dermatophytosis include KOH preparation showing refractile, long, smooth, undulating, branching, and septate hyphal filaments with or without arthroconidiospores; culture and sensitivity may yield the diagnosis but it takes 7-14 days for colony growth; hemotoxylin and eosin stain may be used in diagnosis of Majocchi's granuloma in which KOH examination of scale may be false negative. Polymerase chain reaction (PCR) testing may be used to identify various dermatophytic infections and even help in evaluating drug resistances of different species of dermatophytes.
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Laboratory Findings
Specimen collection
Scrapings should be collected from active margin and transported in a presterilized black chart paper which keeps the specimen dry thus, preventing over growth of bacterial contaminants. Tinea capitis may be diagnosed via dermoscopy.
Direct microscopic examination
- Treatment of skin specimen with 10–20 percent potassium hydroxide (KOH) is a convenient bedside tool to provide evidence of dermatophytic infection.[1]
- Positive scrapings are characterized by:
- Refractile, long, smooth, undulating, branching, and septate hyphal filaments with or without arthroconidiospores.
- Fluorescent staining of the cell wall is the most sensitive method to microscopically detect fungi in skin scales as well as in specimens from nails and hair.
Culture and antifungal sensitivity
- Sabouraud dextrose agar (SDA, 4% peptone, 1% glucose, agar, water) is the most commonly used isolation media for dermatophytosis and serves as the medium for fungal growth.[2][3][1]
- The development of colony takes 7–14 days.
- Modified culturing techniques, with addition of gentamicin, chloramphenicol and cycloheximide is more selective for dermatophytes, as chloramphenicol inhibits the growth of saprophytic fungus.
- Dermatophyte test medium is an alternative to isolation media that contain pH indicator phenol red. It is incubated at room temperature for 5–14 days.
- Dermatophytes utilize the protein resulting in excess ammonium ion and alkaline environment which turn the medium from yellow to bright red.
Hematoxylin and eosin staining
- Histology may be used in diagnosis of Majocchi's granuloma in which KOH examination of scale may be false negative.[4][5][6]
- Hyphae may be visualized in stratum corneum on hematoxylin and eosin staining.
- Special stains most commonly used are:
- Periodic acid-Schiff
- Gomori methanamine silver
Dermoscopy
- Tinea capitis may show:[7][8]
- Comma hairs, which are slightly curved, fractured hair shafts
- Corkscrew hair
- Broken hair
- Tinea corporis may show:
- Involvement of vellus hair
Polymerase chain reaction and nucleic acid sequence based amplification
These tests not only help in the rapid and early diagnosis of infection but also help in determining drug resistance, and include:[9][10][11]
- Uniplex PCR for direct dermatophyte detection in clinical samples:
- A PCR for the direct detection of dermatophytes in skin scales may be used for diagnosis. PCR-ELISA assay separately identifies numerous dermatophyte species.
- Multiplex PCR for fungal detection in dermatophytes:
- Commercially available multiplex PCR tests enable simultaneous amplification of 21 dermatomycotic pathogens with subsequent DNA detection by means of agarose gel electrophoresis.
References
- ↑ 1.0 1.1 Kelly BP (2012). "Superficial fungal infections". Pediatr Rev. 33 (4): e22–37. doi:10.1542/pir.33-4-e22. PMID 22474120.
- ↑ Ecemis T, Degerli K, Aktas E, Teker A, Ozbakkaloglu B (2006). "The necessity of culture for the diagnosis of tinea pedis". Am. J. Med. Sci. 331 (2): 88–90. PMID 16479181.
- ↑ Rezabek GH, Friedman AD (1992). "Superficial fungal infections of the skin. Diagnosis and current treatment recommendations". Drugs. 43 (5): 674–82. PMID 1379146.
- ↑ Al-Amiri A, Chatrath V, Bhawan J, Stefanato CM (2003). "The periodic acid-Schiff stain in diagnosing tinea: should it be used routinely in inflammatory skin diseases?". J. Cutan. Pathol. 30 (10): 611–5. PMID 14744085.
- ↑ Bressan AL, Silva RS, Fonseca JC, Alves Mde F (2011). "Majocchi's granuloma". An Bras Dermatol. 86 (4): 797–8. PMID 21987154.
- ↑ Feng WW, Chen HC, Chen HC (2006). "Majocchi's granuloma in a 3-year-old boy". Pediatr. Infect. Dis. J. 25 (7): 658–9. doi:10.1097/01.inf.0000224312.87417.fc. PMID 16804445.
- ↑ Lacarrubba F, Verzì AE, Micali G (2015). "Newly described features resulting from high-magnification dermoscopy of tinea capitis". JAMA Dermatol. 151 (3): 308–10. doi:10.1001/jamadermatol.2014.3313. PMID 25471133.
- ↑ Arrazola-Guerrero J, Isa-Isa R, Torres-Guerrero E, Arenas R (2015). "[Tinea capitis. Dermoscopic findings in 37 patients]". Rev Iberoam Micol (in Spanish; Castilian). 32 (4): 242–6. doi:10.1016/j.riam.2014.09.002. PMID 25728878.
- ↑ Miyajima Y, Satoh K, Uchida T, Yamada T, Abe M, Watanabe S, Makimura M, Makimura K (2013). "Rapid real-time diagnostic PCR for Trichophyton rubrum and Trichophyton mentagrophytes in patients with tinea unguium and tinea pedis using specific fluorescent probes". J. Dermatol. Sci. 69 (3): 229–35. doi:10.1016/j.jdermsci.2012.11.589. PMID 23287391.
- ↑ Sahoo AK, Mahajan R (2016). "Management of tinea corporis, tinea cruris, and tinea pedis: A comprehensive review". Indian Dermatol Online J. 7 (2): 77–86. doi:10.4103/2229-5178.178099. PMC 4804599. PMID 27057486.
- ↑ Spiliopoulou A, Bartzavali C, Jelastopulu E, Anastassiou ED, Christofidou M (2015). "Evaluation of a commercial PCR test for the diagnosis of dermatophyte nail infections". J. Med. Microbiol. 64 (Pt 1): 25–31. doi:10.1099/jmm.0.079962-0. PMID 25418736.