Investigations
1st investigations to order
potassium hydroxide (KOH) microscopy
Test
Skin scrapings and fragments of nail clippings can be examined under the microscope.
Aids in confirming the diagnosis when unclear clinically.
Must be used to confirm nail infection before starting treatment.
In tinea capitis, fungal spores will be noted in most cases within the hair cells (endothrix). Spores can also be noted on the hair shaft either as a late finding of endothrix or in cases of less common ectothrix infections.
Result
hyphae (branching, rod-shaped filaments of uniform width with septa)
Investigations to consider
dermoscopy
Test
Non-invasive tool for the diagnosis and follow-up of hair and scalp disorders.[27]
Scalp dermoscopy is a valuable and simple technique for the assessment of tinea infection of the scalp.
Result
typical dermoscopic findings characteristic of tinea capitis include: black dots, comma hairs (short hairs that bend and grow back toward the scalp, resembling a comma), and corkscrew hairs (short hairs that are coiled up like a corkscrew)[17]
fungal culture
Test
Useful to confirm the diagnosis of onychomycosis when long-term oral therapy is being considered, especially after negative KOH microscopy but high index of suspicion for tinea unguium.
Also recommended to aid diagnosis of tinea capitis, and in multisite tinea.
Result
growth of dermatophyte species
polymerase chain reaction (PCR)
Test
PCR is a fast and relatively inexpensive way to confirm diagnosis of fungal nail infection.[26]
Result
identification of the causative fungi in nail specimens
Wood lamp examination (ultraviolet light)
Test
Of limited value: used for diagnosing a minority of tinea capitis. Zoophilic Microsporum species fluoresce blue-green (these account for a very small percentage of tinea capitis diagnoses in developed countries).
A brown, scaly rash in the scrotum or axilla, erythrasma is caused by the bacterium Corynebacterium minutissimum. This infection fluoresces brilliant coral red under a Wood lamp. Tinea cruris or cutaneous candidal infections in this area do not fluoresce.
Useful for distinguishing pityriasis versicolor, a yeast infection causing scaly patches on the trunk, from tinea infections, as pityriasis fluoresces pale yellow to white.
Result
fluorescence of skin lesion under ultraviolet light
Emerging tests
reflectance confocal microscopy
Test
High-resolution imaging technique for non-invasive diagnosis; requires no sampling or previous preparation.[28]
Further studies are needed to compare with conventional diagnostic techniques.
Result
thin, highly reflective, longitudinal structures with a serpentine shape
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