A 25-year-old female presents to the clinic for evaluation of hair changes. She reports having hair loss and breakage on the vertex scalp. On exam, you note she has coarse hairs in this region and you decide to examine one of the hairs under light microscopy which shows the finding below.

Which of the following explains this finding?

A. PADI3 mutation

B. T. tonsurans

C. ERCC2 and ERCC3

D. Heat damage

Rationale: Hair shaft abnormalities are important to know and recognize as they can open the window to identifying certain genodermatoses or understanding patients' hair care practices. A helpful tip for evaluating a patient with brittle non-specific hair loss is to evaluate the hairs with light microscopy for any overt hair shaft abnormalities. 

Correct answer: D. Heat damage

The photograph above shows cavitations within the follicle known as bubble hairs; wet hairs can develop this finding when exposed to enough heat from a hair dryer or hair straightener. It is important to counsel patients on appropriate hair practices to avoid further damage and fracture of the hair follicle. Bubble hairs and the associated fractures and/or alopecia are reversible with the elimination of excessive heat trauma. 

Incorrect answers:

A. PADI3 mutations can be seen in central cicatricial centrifugal alopecia (CCCA) and uncombable hair syndrome. Uncombable hair syndrome typically presents as a young child with blonde hair often with a spun glass appearance. Light microscopy can show pili trianguli et canaliculi or a longitudinal groove (pictured below). 

B. T. tonsurans is a dermatophyte and the most common cause of tinea capitis in the United States and United Kingdom. T. tonsurans characteristically presents as an endothrix infection with growth within the hair follicle shaft seen in the picture below. 

C. ERCC2 and ERCC3 mutations are seen in trichothiodystrophy (TTD) which can include a variety of phenotypes. Some findings include sun sensitivity, lamellar ichthyosis, intellectual disability, decreased fertility, brittle nails, and fragile hair. The characteristic hair finding shown below is called the "tiger-tail" sign due to alternating dark and light bands seen in polarized light microscopy; these bands are due to abnormal sulfur content in the hair. Although I am not sure of the original creator of this mnemonic, a helpful way for me to remember the connection between these genes and TTD is to say the following in a cheerleading chant: "E-R-C-C-two-and-three, tri-cho-thi-o-dys-tro-phy!"

Additional reading at Fitzpatrick's Dermatology Chapter 89: Hair Shaft Disorders

1. Savitha, AS; Sacchidanand, S; Revathy, TN. Bubble Hair and Other Acquired Hair Shaft Anomalies due to Hot Ironing on Wet Hair. International Journal of Trichology 3(2):p 118-120, Jul–Dec 2011. 

2. Albers, Lauren N; Maley, Alexander M; MacKelfresh, Jamie B. Blowing Bubbles: Dermoscopy of Bubble Hair. International Journal of Trichology 9(3):p 122-123, Jul–Sep 2017. | DOI: 10.4103/ijt.ijt_11_17

3. Li YM, Diaz-Perez JA, Obayomi A, Galimberti F, Romanelli P, Tosti A. A review of bubble hair deformity. Int J Dermatol. 2023 Mar;62(3):428-431. doi: 10.1111/ijd.