Master Tinea Versicolor for USMLE

The malassezia fungus flourishes through the degradation of fatty acids. As such, those areas of the body that produce increased amounts of sebum, such as those found on the upper back and shoulders are therefore more commonly affected. The degradation of lipids also produces fatty acids that are damaging to melanocytes.

As a result of the degradation of lipids discussed previously, the fatty acids produced damage surrounding melanocytes and can cause hypopigmented or hyperpigmented patches.

Infection with the fungal organism Malassezia furfur is responsible for pityriasis versicolor. This coccal fungus is essentially the only fungus considered part of normal human flora and requires fatty acids for survival, making it a prime candidate for locations that produce copious amounts naturally, like the trunk and proximal upper extremities indicated previously. Microscopic examination of this oil-loving yeast via lesion scrapings treated with KOH prep reveal a characteristic spaghetti and meatballs appearance, which are the hyphae and yeast, respectively.

Considering that M. furfur requires fatty acids for survival and human sweat contains more than adequate amounts, it follows that hot, humid weather serves to exacerbate these lesions and the associated cutaneous symptoms.

As mentioned previously, the very pathophysiologic nature of Malassezia furfur preferring the degradation of fatty acids leads to damage to surrounding melanocytes. This allows the classic presentation of pityriasis versicolor as hypopigmented patches with well demarcated borders and fine scales.

The damage to the adjacent melanocytes from fatty acid breakdown can alternatively result in hyperpigmented patches with well demarcated borders and fine scales.

Diagnosing pityriasis versicolor is made by scraping the lesion and using a KOH prep which results in a characteristic microscopic appearance resembling the classic Italian dish of spaghetti and meatballs. These structures are the hyphae and yeast, respectively.

Microscopic examination of lesion scrapings in individuals with pityriasis versicolor demonstrates mildly variable forms of fragmented, truncated, curved, septate hyphae coupled with clusters of yeast cells to produce the classic spaghetti and meatballs appearance.

As expected in the treatment of a superficial, cutaneous fungal infection, topical antifungals such as miconazole are utilized first. However, recurrence is not unlikely and severe infections may require oral antifungal therapy.

An alternative therapy used in the treatment of pityriasis versicolor is selenium sulfide, which finds its therapeutic modality in its capacity to shed infected stratum corneum to eradicate the fungus. It is also commonly found in shampoos used to combat dandruff.

Zinc pyrithione is another dandruff shampoo component that finds employment in treating pityriasis versicolor. It exerts its antifungal properties by disrupting membrane transport processes in fungi.