Dermatology · Fungal Infections
The facts most likely to be tested
Tinea versicolor is caused by the overgrowth of the dimorphic yeast known as Malassezia furfur (formerly Pityrosporum orbiculare).
The clinical presentation features hypopigmented, hyperpigmented, or erythematous macules and patches primarily on the upper trunk and shoulders.
The classic microscopic finding on potassium hydroxide (KOH) preparation is the spaghetti and meatballs appearance representing short hyphae and yeast clusters.
Lesions fail to tan upon sun exposure because the fungus produces azelaic acid, which inhibits tyrosinase and disrupts melanin production.
The Wood's lamp examination reveals a characteristic yellow-green fluorescence of the affected skin areas.
First-line treatment for localized disease is topical antifungal therapy such as selenium sulfide or ketoconazole shampoo.
Systemic therapy with oral fluconazole or itraconazole is reserved for extensive or refractory cases.
Vignette unlocked
A 24-year-old male presents to the clinic complaining of persistent skin discoloration on his chest and back that has become more noticeable after returning from a beach vacation. Physical examination reveals multiple hypopigmented, scaly macules distributed across his upper torso. He notes that these areas do not tan despite sun exposure. A KOH preparation of the skin scrapings is performed in the office. The patient has no history of immunosuppression or recent antibiotic use.
What is the most likely diagnosis and the expected microscopic finding?
Tinea versicolor; spaghetti and meatballs appearance.
The vignette describes the classic presentation of Tinea versicolor (hypopigmented patches on the trunk that fail to tan), which is confirmed by the pathognomonic 'spaghetti and meatballs' appearance on KOH prep.
Full handout
High yield triage
Etiology / Epidemiology
Caused by Malassezia furfur (yeast) in hot, humid climates. Common in young adults.
Clinical Manifestations
Hypo/hyperpigmented macules with fine scaling; spaghetti and meatballs appearance on microscopy.
Diagnosis
KOH preparation is the gold standard; shows short hyphae and clusters of budding yeast.
Treatment
Selenium sulfide or ketoconazole shampoo; avoid oral antifungals if liver disease present.
Prognosis
High recurrence rate; pigment changes may persist for months after fungal clearance.
Full handout
Epidemiology & Etiology
Primarily affects adolescents and young adults living in tropical or humid environments. The causative agent is the lipophilic yeast Malassezia furfur (formerly Pityrosporum orbiculare). It is a commensal organism that becomes pathogenic under specific environmental triggers.
Pertinent Anatomy
Involves the stratum corneum of the epidermis. Lesions typically localize to the upper trunk, back, and proximal extremities where sebaceous activity is highest.
Pathophysiology
The yeast produces dicarboxylic acids (e.g., azelaic acid) which inhibit tyrosinase in melanocytes, leading to hypopigmentation. Conversely, inflammatory responses can cause hyperpigmentation. The organism thrives on skin lipids, explaining its predilection for seborrheic areas.
Clinical Manifestations
Patients present with well-demarcated, round-to-oval macules that fail to tan. The hallmark is fine, superficial scale that is easily elicited by scratching (the Besnier sign). Under a Wood's lamp, lesions exhibit a characteristic yellow-green fluorescence.
Diagnosis
The KOH preparation is the diagnostic gold standard, revealing the classic spaghetti and meatballs pattern of short hyphae and yeast clusters. Biopsy is rarely required but would show organisms confined to the stratum corneum.
Treatment
First-line therapy is topical selenium sulfide or ketoconazole shampoo applied to the body and left for 10 minutes before rinsing. For extensive or refractory cases, oral fluconazole or itraconazole may be used. Oral ketoconazole is associated with hepatotoxicity and is generally avoided.
Prognosis
While the infection is easily treated, pigmentary changes often persist for weeks to months. Prophylactic treatment with topical agents once or twice monthly is recommended for patients with frequent recurrences.
Differential Diagnosis
Vitiligo: lacks scale and fluorescence
Pityriasis rosea: presents with a herald patch and Christmas tree distribution
Tinea corporis: typically annular with central clearing
Guttate psoriasis: associated with recent streptococcal infection
Seborrheic dermatitis: involves scalp, eyebrows, and nasolabial folds