Common Fungal Diseases of Skin
A 10 yr old boy with scalp boggy swelling with multiple sinuses, easy pluck able hair, lymph nodes enlarged in occipital region, what to be done 4 diagnosis? (AIIMS May 2012)
KOH mount. It is a case of Tinea capitis
Laboratory diagnosis of tinea capitis depends on examination and culture of skin rubbings, skin scrapings, or hair plucking (epilated hair) from lesions.
1). Infected hairs appearing as broken stubs are best for examination. They can be removed with forceps without undue trauma or collected by gentle rubbing with a moist gauze pad; broken, infected hairs adhere to the gauze.
2). Selected hair samples are cultured or allowed to soften in 10% potassium hydroxide (KOH) before examination under the microscope.
3). Examination of KOH preparations (KOH mount) usually determines the proper diagnosis if a tinea infection exists.
4). Conventional sampling of a kerion can be difficult. Negative results are not uncommon in these cases. The diagnosis and decision to treat lesions of kerion may need to be made clinically. A moistened standard bacteriological swab taken from the pustular areas and inoculated onto the culture plate may yield a positive result.
5). Microscopic examination of the infected hairs may provide immediate confirmation of the diagnosis of ringworm and establishes whether the fungus is small-spore or large-spore ectothrix or endothrix.
6). Culture provides precise identification of the species for epidemiologic purposes.
7). Primary isolation is carried out at room temperature, usually on Sabouraud agar containing antibiotics (penicillin/streptomycin or chloramphenicol) and cycloheximide (Acti-Dione), which is an antifungal agent that suppresses the growth of environmental contaminant fungi.
8). In cases of tender kerion, the agar plate can be inoculated directly by pressing it gently against the lesion.
9). Most dermatophytes can be identified within 2 weeks, although T verrucosum grows best at 37°C and may have formed only into small and granular colonies at this stage. Identification depends on gross colony and microscopic morphology.
10). Specimens should be inoculated on to primary isolation media, such as Sabouraud dextrose, and incubated at 26-28°C for 4 weeks. The growth of any dermatophyte is significant.