How can I differentiate pityriasis versicolor from other similar skin conditions during a clinical examination?

To differentiate pityriasis versicolor from other similar skin conditions during clinical examination, focus on the following key features:

• Appearance: Pityriasis versicolor typically presents as well-demarcated, finely scaling macules or patches that may be hypopigmented, hyperpigmented, or erythematous, often on the trunk, neck, and upper arms. The scaling is subtle and may be more apparent when the skin is stretched (the 'cigarette paper' scale).
• Distribution: Lesions are usually multiple and confluent, favoring seborrhoeic areas but sparing the face in most cases. This distribution helps distinguish it from tinea corporis, which often has annular, raised, scaly borders.
• Wood's light examination: Although not routinely available in primary care, a Wood's lamp may show a characteristic yellow-green fluorescence in about one-third of cases, aiding diagnosis. However, absence of fluorescence does not exclude pityriasis versicolor as some causative Malassezia species do not fluoresce ¹.
• Microscopy of skin scrapings: Confirmatory diagnosis can be made by examining skin scrapings under microscopy after potassium hydroxide preparation, revealing the characteristic 'spaghetti and meatballs' appearance of yeast and short hyphae, which differentiates it from dermatophyte infections ¹.
• Non-contagious nature and recurrence: Pityriasis versicolor is caused by Malassezia yeast normally present on skin and is not contagious, unlike some other fungal infections. Recurrence is common, especially in warmer months, which can help differentiate it from other dermatoses ¹.
• Clinical context and patient skin type: In darker-skinned individuals, hypopigmented lesions may be more prominent and can mimic other hypopigmenting disorders; careful clinical and microscopic evaluation is essential (Kallini et al., 2014).
• Exclusion of other diagnoses: Consider other fungal infections such as tinea corporis, which usually have more inflammatory borders and central clearing, and do not show the fine scaling of pityriasis versicolor. Steroid-modified tinea may present atypically and should be considered if topical corticosteroids have been used ¹,².

Summary: Clinical differentiation relies on lesion morphology (fine scaling, color variation), typical distribution, microscopy confirmation, and, if available, Wood's light examination. Awareness of the non-contagious nature and recurrence pattern also aids differentiation from other skin conditions ¹[(Kallini et al., 2014)].