What is the underlying mechanism of a 17-year-old boy's nonpruritic, hypopigmented macules on the chest and trunk, with fine scaling, after returning from Puerto Rico and starting a new laundry detergent, with a history of type 1 diabetes mellitus (T1DM) and family history of Hashimoto thyroiditis and acne?

From the Guidelines

The most likely underlying mechanism of this patient's symptoms is increased growth of Malassezia globosa. This patient is presenting with tinea versicolor, a common superficial fungal infection characterized by hypopigmented macules with fine scaling. The causative organism is Malassezia globosa, a lipophilic yeast that is part of normal skin flora but can overgrow under certain conditions. Some key points to consider in this diagnosis include:

• Risk factors for tinea versicolor include warm, humid environments (like Puerto Rico) 1, immunocompromised states (the patient has diabetes), and genetic predisposition.
• The hypopigmentation occurs because the fungus produces azelaic acid, which inhibits tyrosinase activity in melanocytes, leading to decreased melanin production.
• The fine scaling observed when scraping the lesions (positive "scratch test") is characteristic of this condition and represents the fungal elements in the stratum corneum.
• Treatment typically involves topical antifungal medications such as selenium sulfide, ketoconazole, or terbinafine.
• In more extensive cases, oral antifungal therapy may be necessary. It's also important to differentiate tinea versicolor from other conditions that may cause hypopigmentation, such as vitiligo, which is characterized by the destruction of melanocytes and often has a different clinical presentation 1.

From the Research

Patient's Symptoms

The patient presents with a nonpruritic rash on his chest for 1 week, which started after returning from a trip to Puerto Rico. The rash is characterized by multiple, nontender, round, hypopigmented macules on the chest and trunk, with fine scaling when scraped with a spatula.

Possible Causes

Based on the symptoms, the possible causes of the patient's condition are:

• Autoimmune destruction of melanocytes
• Increased sebum production
• Deficiency of tyrosinase
• Increased growth of Malassezia globose
• Antigen uptake by Langerhans cells
• Infection with Trichophyton rubrum

Most Likely Underlying Mechanism

The most likely underlying mechanism of the patient's symptoms is:

• Increased growth of Malassezia globose, as the patient's symptoms are consistent with tinea versicolor, a common superficial fungal infection caused by Malassezia species, notably M. globosa, M. furfur, and M. sympodialis 2, 3. The characteristic clinical features of tinea versicolor, including scaly hypopigmented or hyperpigmented macules/patches, primarily located on the upper trunk, neck, and upper arms, match the patient's symptoms 2. The diagnosis of tinea versicolor is usually based on characteristic clinical features, and a potassium hydroxide preparation test can be performed to reveal numerous short, stubby hyphae intermixed with clusters of spores 2.

Treatment Options

Treatment options for tinea versicolor include:

• Topical antifungal therapy, which has a better safety profile and lower cost compared to systemic treatment 2, 3
• Oral antifungal therapy, which is typically reserved for patients with extensive disease, frequent recurrences, or disease that is refractory to topical therapy 2, 3, 4, 5