CLINICAL ISSUES :: MOLECULAR DIAGNOSTICS FOR DERMATOMYCOSIS


Photo courtesy of EUROIMMUN US


Molecular diagnostics for sensitive detection of dermatomycosis species


By Jackie Weiss, PhD D


ermatomycosis of the hair, skin, or nails is one of the most prevalent fungal infections worldwide, affecting 20–25% of the global population.1


The condition is caused by ke-


ratinolytic fungi called dermatophytes, in addition to molds and yeasts.2


Dermatophytes are classified into six pathogenic


genera: Microsporum, Trichophyton, Epidermophyton, Nannizzia, Lophophyton, and Arthroderma. Additionally, dermatophytes are categorized as anthropophilic, zoophilic, or geophilic according to their natural habitat.3 Clinical presentation varies depending on the site of infection, type of fungus, and immune response of a patient but frequently include rash, itchy skin, hair loss, or thickened nails.3


Although


antifungal medications are effective, dermatomycosis remains undertreated.4


In addition to causing permanent damage to the


affected area, dermatomycosis can progress to severe disease in elderly and immunocompromised patients if left untreated.5-7 Furthermore, improper treatment will not only fail to clear the infection and prevent further spread but may also contribute to the development of antifungal resistance.5


Importantly, health-


care providers must first identify the fungal species causing infection to prescribe the most effective treatment. Dermatomycosis can be difficult to diagnose clinically, as symptoms may resemble other skin disorders.8


Therefore,


laboratory diagnostics are required for a definitive diagnosis. While traditional dermatomycosis diagnostics may take several weeks or are unable to identify dermatophyte species, molecular methods facilitate quick, species-specific determination.


Conventional diagnostics Fungal Culture: Fungal culture using hair, skin, or nail specimens is a common method for detecting dermatomycosis and identify- ing fungal species.9


Culture involves plating and incubating the


patient sample for 4–6 weeks in sample media. Fungal species can then be visually identified based on morphological charac- teristics such as colony size, pigmentation, shape, and type of growth.9


However, accurate species identification based on colony


morphology requires well-trained mycology staff. While culture allows the identification of fungal species, the long incubation time delays species identification and subsequent treatment.


14 | SEPTEMBER 2023 MLO-ONLINE.COM Additionally, fungal culture has limited sensitivity for detection


of dermatomycosis. Some fungal species do not grow in culture, and recent systemic or topical use of antifungal treatments can prevent fungi from growing.2


In these cases, a sample is at risk of


being incorrectly identified as negative. False negative results may also stem from improper specimen collection or insufficient sample material, whereas false positives may result from contamination.9 Microscopy: Direct microscopy of hair, skin, and nail specimens is commonly performed to assess the presence or absence of pathogenic fungi. As with culture, technical expertise is required to differentiate between dermatophytes, molds, and yeasts.9


While


microscopy is less time-intensive than fungal culture, microscopy cannot be used to identify fungal species or indicate viability of the pathogen. Furthermore, microscopy has a high false negative rate of 35% for the diagnosis of dermatomycosis.10 Prior to microscopic evaluation, specimens are often digested in 10–20% potassium hydroxide (KOH), used as a clearing agent.11 This technique facilitates the visualization of hyphae and spores by digesting the keratin surrounding the fungi. However, usage of KOH preparation may lead to false negative results in 5–15% of cases.3


used to improve sensitivity.12


Additional stains, such as Calcofluor White (CW), can be Periodic acid-Schiff (PAS) staining


is another common method for detection of fungal pathogens. PAS staining reacts with aldehyde groups in fungal cell wells, allowing visualization of hyphae and yeast-forms of fungi. Previous work has shown that for diagnosis of onychomycosis (OM), nail plate biopsy with PAS stain is more sensitive than culture, KOH preparation, and CW stain.13


Molecular diagnostics Molecular methods for dermatomycosis diagnosis include poly- merase chain reaction (PCR), real-time PCR, DNA microarray, and next-generation sequencing (NGS). These techniques involve direct detection of genetic material and provide a faster, more accurate alternative to conventional diagnostics. Importantly, molecular methods enable rapid identification of fungal species, which allows patients to receive more expedient and appropriate treatments. PCR: Polymerase chain reaction (PCR)-based assays use primers to amplify fungi-specific DNA sequences in a sample.14,15


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48