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Diagnostic Techniques

»	What is the most sensitive office laboratory test for diagnosing dermatophyte infections of the skin?
»	How is a KOH examination performed?
»	What laboratory tests are useful for diagnosing tinea capitis?
»	What is a Wood’s light or lamp? How is it useful in skin diseases?
»	Name common culture media used for isolating dermatophytes.
»	Describe a simple test for tinea versicolor other than a KOH preparation.
»	What is a Tzanck preparation or smear?
»	What is the best method of diagnosing scabies?
»	How do you diagnose mite bites acquired from an animal?
»	How do you diagnose lice infestation?
»	What is the diagnostic test of choice for a patient presenting with a suspected syphilitic chancre on his penis?
»	How is secondary syphilis diagnosed?
»	How long do serologic tests for syphilis remain positive?
»	In patients with symptomatic gonococcal urethritis, how efficacious is a Gram stain of the exudate in comparison to a culture utilizing selective media for gonococcus?
»	What is the best way to diagnose allergic contact dermatitis?
»	How are patch tests applied?
»	In what diseases is a skin biopsy helpful?
»	When are shave biopsies indicated?
»	What are the indications for punch biopsies?
»	Describe the indications for an excisional or incisional biopsy.
»	Define and describe direct immunofluorescence of the skin.
»	Name some skin diseases in which DIF is helpful in making a diagnosis.
»	How does indirect immunofluorescence of the skin differ from direct immunofluorescence of the skin?
»	Is ELISA ever used for the diagnosis of immunobullous disease?
»	How are bacterial skin cultures performed, and when are they useful?

Name common culture media used for isolating dermatophytes.

Dermatophyte test media (DTM) and Sabouraud’s dextrose agar, with or without antibiotics (e.g., Mycosel agar, Mycobiotic agar), are the two most common types of culture media used. Many dermatologists prefer DTM because it has the advantage of a color indicator that changes the media from yellow to red when a dermatophyte is present. DTM is 95% to 97% accurate in differentiating dermatophytes from nondermatophytes. Sabouraud’s dextrose agar is a standard in mycology laboratories and also in many dermatologists’ offices. It consists of dextrose (energy source), peptone (protein source), and agar (for a firm surface). Antibiotics can be added to suppress bacterial contaminants, and cycloheximide is added to suppress yeasts and nondermatophytes. Plain Sabouraud’s agar is an especially good culture medium for Candida albicans.

Taplin D, Zaias N, Rebell G, Blank H: Isolation and recognition of dermatophytes on a new medium (DTM), Arch Dermatol 99:203–209, 1969.

Head E: Laboratory diagnosis of the superficial fungal infections, Dermatol Clin 2:93–108, 1984.