Question: 

A 4-year-old boy living in the United States comes to the office for evaluation of hair loss with the findings shown in the photograph below. During the exam, you also note palpable occipital lymphadenopathy. His mother states that they have several pets at home as well as a family history of autoimmune thyroid disease. What is the most common etiology of the patient's hair loss?

A. Trichophyton tonsurans

B. Microsporum canis

C. T-cell mediated destruction of the hair follicles

D. Ebstein Barr Virus

E. Black fly (Simulium spp)

Rationale: The vignette consists of a patient with a circular patch of hair loss, the presence of scale, small fractured hairs, and palpable lymphadenopathy which is consistent with tinea capitis. Fungal culture can confirm the diagnosis and determine the specific pathogen. The most common pathogenic fungi varies based on the country of origin. Below are several other examples of tinea capitis - note the presence of annular papules on the face in the first picture which can be a clue to the diagnosis.

Correct answer: A. Trichophyton tonsurans

T. tonsurans is the most common culprit of tinea capitis within the United States and in many countries across the world. It does not fluoresce with Wood's light. Some patients present with the finding of "black dot" tinea (pictured below) which is due to the presence of fractured hair follicles from the endothrix infection.  

B. Microsporum canis is the second most common culprit in the United States and the most common fungal organism causing tinea capitis in Europe.

C. The presence of scale and lymphadenopathy is not consistent with alopecia areata. The family history of autoimmunity was a distractor but represents a common situation observed in clinical practice. 

D. EBV can cause significant cervical lymphadenopathy but is not associated with scaling and hair loss. 

E. Fogo selvagem is an endemic variant of pemphigus foliaceous thought to be related to the Simulium species of black fly due to the high prevalence of this disorder in remote areas of Brazil with high concentrations of black flies. Although pemphigus foliaceous does present on the scalp, lesions typically have more crusting, erosions, and a "cornflake" type appearance which are not seen in this clinical vignette. 

Additional reading at Fitzpatrick's Dermatology Chapter 160: Superficial Fungal Infection

References:

1. Mirmirani P, Tucker LY. Epidemiologic trends in pediatric tinea capitis: a population-based study from Kaiser Permanente Northern California. J Am Acad Dermatol. 2013 Dec;69(6):916-21. doi: 10.1016/j.jaad.2013.08.031. Epub 2013 Oct 3. PMID: 24094452.

2. Gold JAW, Benedict K, Lockhart SR, Lipner SR. Epidemiology of tinea capitis causative species: An analysis of fungal culture results from a major United States national commercial laboratory. J Am Acad Dermatol. 2023 Aug;89(2):382-384. doi: 10.1016/j.jaad.2023.03.037. Epub 2023 Mar 31. PMID: 37003477; PMCID: PMC10691499.

3. Rodríguez-Cerdeira C, Martínez-Herrera E, Szepietowski JC, Pinto-Almazán R, Frías-De-León MG, Espinosa-Hernández VM, Chávez-Gutiérrez E, García-Salazar E, Vega-Sánchez DC, Arenas R, Hay R, Saunte DM. A systematic review of worldwide data on tinea capitis: analysis of the last 20 years. J Eur Acad Dermatol Venereol. 2021 Apr;35(4):844-883. doi: 10.1111/jdv.16951. Epub 2020 Nov 17. PMID: 32976663.