1. Background

• the infectious agent is the dimorphic yeast Pityrosporon orbiculare (Malassezia furfur) which is a component of the normal skin flora and a normal human saprophyte
• conditions which affect the balance of the normal skin flora may predispose to Pityriasis Versicolor:
  • high cortisol levels (Cushing's Disease)
  • steroid use
  • excessive sweating
  • debilitating disease

2. Pathogenesis

• in affected areas, the Pityrosporum produces hundreds of spores which settle in the stratum corneum -> from the spores, short hyphae develop which are keratinolytic resulting in the fine scales
• the distinctive macules do not become clinically apparent until the hyphae have developed
• these macules are usually centred around a follicle which may act as a likely origin and retreat for the Pityrosporum cells; this accounts for the observations that the macules usually begin in a perifollicular location and for the relapsing nature of the infection
• the hypopigmentation that can occur is due to:
  • the infectious process lessening melansome transfer
  • the interaction of the fungus with surface lipids producing dicarboxylic acids which inhibit the enzyme tyrosinase in the skin melanocytes

1. Skin Manifestations

1. Light Microscopy

• thick-walled spores and hyphae can be demonstrated on direct examination of the scales using KOH

1. Selenium Sulfide (Selsun)

• apply a thin layer of 2.5% selenium sulfide to the entire body (except face and genitals) for 10 minutes then rinse off with water and repeat for 7 consecutive nights; repeat again at the first sign of relapse
• the sulfur kills the hyphae and reduces the yeast population
• bath or shower twice a day and rub the lesions with soap and hot water to remove the scaling and dislodge the fungi - may also use Selsun Blue Shampoo

2. Antifungal Agents

• miconazole, clotrimazole, or ketoconazole po bid for 2-4 weeks

3. Prognosis

• good but may relapse
• residual hypopigmentation may take a few months to resolve and in the summer may need to be covered with sunscreen