Pityriasis Versicolor
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Direct answer
Malassezia yeasts manufacture azelaic acid, a dicarboxylic acid that inhibits tyrosinase, which is why pityriasis versicolor leaves finely scaled, hypopigmented (sometimes hyperpigmented) macules on the trunk and neck of young adults in hot, humid climates. KOH microscopy of the scale shows short, thick hyphae and budding yeast clusters — the "spaghetti and meatballs" pattern — and treatment with topical azoles, selenium sulphide or short oral antifungals clears the organism while the pigment takes months to normalise. For NEET-PG Medicine, its differentials against vitiligo and tuberculoid leprosy are the exam gold.
What you must remember
- Malassezia is a lipophilic, commensal yeast flourishing in sebum-rich sites: chest, back, neck, upper arms.
- Hypopigmentation results from azelaic acid inhibiting tyrosinase, plus direct interference with melanosome function; pigment changes are thus functional, not destructive.
- Lesions are fine, branny-scaled macules of varying size; scaling is subtle and becomes evident on gentle scraping.
- KOH: short, septate, bent hyphae with grape-like clusters of round budding yeasts — "spaghetti and meatballs".
- Wood's lamp: yellowish-gold fluorescence of lesional scale in many cases.
- Treatment: 2.5% selenium sulphide lotion or ketoconazole 2% shampoo applied like a lotion (leave 5–10 minutes, rinse) nightly for one to two weeks; topical azoles equally effective.
- Extensive or refractory disease: oral fluconazole or itraconazole (single-dose or short weekly regimens per local practice); griseofulvin is ineffective.
- Recurrence is common in Indian summers and monsoons; weekly maintenance washes may be advised during sweat-heavy seasons.
- Pigment takes weeks to months to even out after mycological cure — counsel this explicitly.
How to work through the diagnostic problem it poses
A 21-year-old college student notices pale patches over the chest and back each summer, worsening after football; he has been applying a fairness cream without change. Examination shows confluent, finely furred macules that scale when scratched.
Step one: scrape and KOH the scale — the mixed hyphal-yeast picture confirms pityriasis versicolor on the spot. Step two: distinguish the two exam differentials aloud. Against vitiligo: versicolor retains fine scale, is poorly demarcated, KOH-positive, and never chalk-white depigmented; vitiligo is completely amelanotic, depigmented with crisp margins, and negative on KOH. Against tuberculoid leprosy: the patches of leprosy are hypoanaesthetic with thickened nerves and clear margins, usually fewer and larger — so in the Indian setting, test coarse sensation over any hypopigmented patch and palpate the great auricular and ulnar nerves before settling on a purely cosmetic diagnosis. Step three: treat — ketoconazole shampoo applied to the whole trunk nightly for a week, or fluconazole orally for extensive involvement. Step four: set expectations: the yeast dies quickly, the colour lags by months, and post-inflammatory pigment may need nothing but sun-sensible behaviour. Step five: plan seasonal prophylaxis in a recurrent case — monthly shampoo use through the hot months — and address the sweat, occlusive sportswear and sebum that feed relapse.
Where students slip
The classic slip is labelling every pale patch "vitiligo" and prescribing immunosuppressants for a fungus. The opposite slip in India is missing leprosy: any hypopigmented anaesthetic patch with a thickened adjacent nerve demands sensation testing and referral, not antifungals. Third, candidates expect the pigment to recover with treatment and declare failure at two weeks — mycological cure and cosmetic recovery run on different clocks. Fourth, forgetting that griseofulvin has no role here is a pharmacology favourite: it lacks activity against Malassezia. Finally, do not scrub lesions aggressively; the scale is the specimen, and the diagnosis is read from it.
Frequently asked questions
Why does pityriasis versicolor cause hypopigmentation?
Malassezia produces azelaic acid, a dicarboxylic acid that competitively inhibits tyrosinase and impairs melanin synthesis, so melanocytes are suppressed but not destroyed.
What does KOH microscopy of the scale show?
Short, thick, angulated hyphae alongside clusters of round budding yeast cells — the classic "spaghetti and meatballs" appearance.
How is pityriasis versicolor differentiated from vitiligo?
Versicolor shows fine scale, indistinct borders, truncal distribution and KOH positivity; vitiligo shows chalk-white complete depigmentation with sharp margins and a negative KOH.
Which treatments are effective?
Topical selenium sulphide 2.5%, ketoconazole shampoo or azole creams for one to two weeks; oral fluconazole or itraconazole for extensive disease — griseofulvin is ineffective.
Why must sensation be tested over hypopigmented patches in India?
To exclude tuberculoid leprosy, whose hypopigmented patches are anaesthetic and accompanied by thickened cutaneous nerves — a differential no Indian clinician can afford to miss.