SN5 SHORT NOTE 5M ★ High-yield

Describe Malassezia and the other superficial mycoses.

Microbiology · 2nd Professional — Para-Clinical

Malassezia and Pityriasis Versicolor

Malassezia furfur (and related species) is a lipophilic yeast and a normal commensal of skin rich in sebaceous glands — scalp, face, chest and back
It is lipid-dependent and will not grow on ordinary Sabouraud agar; the medium must be overlaid with olive oil, which is a characteristic and examinable laboratory requirement
Pityriasis (tinea) versicolor — well-demarcated macules on the trunk, neck and upper arms that are HYPOpigmented on dark skin and HYPERpigmented on pale skin (hence "versicolor"), with fine branny scaling brought out by scratching
The hypopigmentation is caused by azelaic acid produced by the yeast, which inhibits tyrosinase in melanocytes — and it persists for months after the fungus is eradicated, which must be explained or the patient will believe the treatment has failed
KOH mount shows the classical "spaghetti and meatballs" appearance — short curved hyphae with clusters of round yeast cells. Wood lamp gives a golden-yellow fluorescence
Favoured by heat, humidity, sweating, oily skin and immunosuppression, so it is extremely common in India and recurs seasonally
Also causes seborrhoeic dermatitis and dandruff; Malassezia folliculitis (itchy monomorphic follicular papules on the back, often mistaken for acne and made worse by antibiotics); and catheter-related fungaemia in neonates receiving intravenous lipid emulsions, which supply exactly the lipid it requires
Treatment — topical ketoconazole or selenium sulphide shampoo applied to the whole trunk; oral fluconazole or itraconazole for extensive or recurrent disease. Terbinafine is ineffective orally against it, although topical terbinafine works — a practical point frequently got wrong

CLINICAL PEARL

The pale patches persist for months after successful treatment, and this must be explained before treatment starts. The yeast is gone within days, but the azelaic acid it produced has already inhibited melanin synthesis, and repigmentation requires sun exposure over weeks to months. A patient not warned of this concludes the treatment failed, buys another cream, and often ends up with a steroid combination — which is how a trivial condition becomes a complicated one.

Other Superficial Mycoses

Condition	Organism	Features
Tinea nigra	Hortaea werneckii — a dematiaceous fungus	A painless brown-black macule on the palm or sole, resembling a stain. Its importance is that it is regularly mistaken for melanoma and biopsied unnecessarily; a KOH mount showing brown septate hyphae settles it
Black piedra	Piedraia hortae	Hard, gritty black nodules firmly attached to the scalp hair shaft; the hair may break. Common in tropical India
White piedra	Trichosporon species	Soft, pale, easily detached nodules on facial, axillary and pubic hair. Trichosporon also causes disseminated infection in the neutropenic, and gives a false-positive cryptococcal antigen test
Otomycosis	Aspergillus niger, A. Fumigatus, Candida	Itching, blocked ear and discharge; A. Niger gives a characteristic black "wet blotting paper" appearance in the canal. Treated by thorough suction clearance with topical antifungals; common in humid climates
Onychomycosis by non-dermatophyte moulds	Scopulariopsis, Fusarium, Aspergillus	Separate these from dermatophyte nail disease, since they respond poorly to terbinafine; repeated isolation is needed to prove significance

Applied Aspects

Explain that repigmentation takes months in pityriasis versicolor, and that the persistence of pale patches does not mean treatment failure
Recurrence is the rule in a humid climate; intermittent prophylactic shampoo use before the hot season is a practical measure
Do not biopsy a palmar pigmented macule before doing a KOH mount; tinea nigra is a trivial condition that has led to unnecessary excision for suspected melanoma
Consider Malassezia folliculitis in "acne" on the back that worsens with antibiotics; it responds to antifungals and not to antibacterials
Ask about intravenous lipid emulsion in a neonate with unexplained fungaemia, and request that the laboratory overlay the culture with oil, or Malassezia will not grow and the blood culture will be reported as negative
Superficial mycoses cause no tissue reaction and are a cosmetic rather than a medical problem — but they cause real distress, and dismissing them is what drives patients to unregulated combination creams
Treat the scalp as well as the trunk in pityriasis versicolor; the scalp is the reservoir from which recolonisation occurs, and treating the visible patches alone guarantees recurrence
Trichosporon causes a false-positive cryptococcal antigen test, which can lead to a patient being treated for cryptococcal meningitis they do not have

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