Laboratory Tests and Ancillaries
Lab testing is not usually needed for the diagnosis. Microscopy may be considered if the diagnosis is unclear; the infection is unresponsive to the regular topical antifungals, and if planning for oral antifungal treatment.
Microscopy
Pityriasis Versicolor_Diagnostics
Potassium hydroxide (KOH) examination of skin scrapings should confirm the diagnosis. Scales or debris are examined under a light microscope after adding a drop of 10-20% KOH solution. Short stubby hyphae and yeast cells will appear as the typical “spaghetti and meatballs” appearance. Calcofluor may be used, but this technique requires utilization of a fluorescence microscope. Malassezia species also stain well with periodic acid-schiff (PAS) or methenamine silver.
Culture
Culture is unnecessary for routine diagnosis. It is difficult to grow Malassezia in standard mycological media.
Wood’s Light Exam
Wood’s light exam may be used to detect subclinical lesions. However, yellowish to white fluorescence is indicative only in approximately 1/3 of cases.