Given the presentation and the unique location of the lesions he was diagnosed with follicular keratosis of the chin (FKC).
This is a rare and poorly understood condition that can be present in older children and young teenagers. In the cases reported by Kanzaki et al.1 were two boys who presented with the condition; it was thought to be associated with rubbing of the chin with their hands when watching TV or reading. The author described improvement with habit change. This condition is usually described in boys, and some cases presented in brothers,2 suggesting a genetic predisposition. Some reports lack a history of rubbing or trauma to the area.
Histopathologic evaluation of the lesions demonstrates dilated hair follicles containing keratotic basophilic material without any signs of inflammation.
Dr. Catalina Matiz
The lesions can be confused with keratosis pilaris (KP). Keratosis pilaris can be described in association with atopic dermatitis and ichthyosis, which were not present in our patient. The lesions usually present on the sides of the cheeks and lateral region of the arms and legs. Compared with follicular keratosis, KP lesions usually present with associated perifollicular erythema. Our patient did not present with lesions on the cheeks or the sides of the arms or legs. Milia can present on the chin of children, usually if there is history of rubbing or trauma, or on a scar. Milia are micro keratin cysts, usually seen in areas of the face. Lichen spinulous is described as rough small follicular papules that present in oval or circular patches that can grow up to 5 cm and spread rapidly. They usually present on the extensor surfaces of the extremities, neck, abdomen, and knees. These lesions are thought to be secondary to infections, have been associated with atopy, and have been seen in patients with atopic dermatitis. There is a probable genetic predisposition. The lesions are usually treated with gentle soaps and moisturizer containing keratolytics like urea or salicylic acid, and in some cases topical retinoids can also be tried. Follicular mucinosis can also present similarly to keratosis follicularis. The lesions present as scaly plaques or as grouped skin color papules on the face, scalp, or the neck that can also be associated with hair loss. Sometimes a biopsy needs to be done to be able to distinguish it from follicular keratosis. There is an increase of mucin around hair follicles and sebaceous glands with associated inflammation and degeneration of the follicular structures. In patients with primary follicular mucinosis the lesions can resolve spontaneously in a couple of years. Lesions can be treated with topical corticosteroids, oral antibiotics like macrolides or tetracyclines, dapsone, and phototherapy.
KFC can be treated with vitamin D analogues. It is usually unresponsive to corticosteroids, keratolytic lotions, and retinoids. Our patient was prescribed calcipotriene.
Dr. Matiz is a pediatric dermatologist at Southern California Permanente Medical Group, San Diego
References
1. Kanzaki T et al. J Am Acad Dermatol. 1992;26(1):134-5.
2. Buechner AA et al. JAMA Dermatol. 2018 Jan 1;154(1):111-2.