Atrophying Keratosis Pilaris: What is this rare form that affects the scalp?

Atrophying keratosis pilaris is a rare dermatosis, primarily occurring during early childhood and childhood, predominantly affecting boys. As a rare disease, it has a very low prevalence, affecting approximately 1 in 1,000,000 individuals. Atrophying keratosis pilaris is characterised by a follicular hyperkeratosis, that is, an overproduction of keratin by the keratinocytes, leading to the formation of hard, red bumps on the surface of the scalp.

This condition is also associated with a progressive scarring alopecia of the scalp, eyebrows, and eyelashes. The hair and eyebrow loss is gradual, and the few studies conducted on this disease report cases of atrophying keratosis pilaris where hair loss occurred over ten years and eyebrow loss over five years. The disease can also manifest as a photophobia, that is, a hypersensitivity to light, a corneal dystrophy, which is an abnormality of the cornea of the eyes, a facial erythema and/or a palmoplantar keratoderma, corresponding to an abnormal thickening of the skin on the soles of the feet.

The exact causes of atrophying keratosis pilaris remain unclear and vary among individuals. However, it appears that there is a strong genetic influence with a suspected autosomal dominant mode of transmission. This means that the "defective" allele is located on a non-sex chromosome and that only one copy of the gene needs to be affected for the condition to develop. A study suggests that the responsible gene is located on Xp22.13-22.2. This is the gene for the protease site 2 of the membrane-bound transcription factor (MBTPS2), necessary for the cleavage of sterol regulatory element-binding proteins (SREBP). The alteration of SREBP cleavage impairs cholesterol and lipid homeostasis in the skin, leading to a defective epidermal differentiation.

Another hypothesis is circulating regarding the origin of atrophying keratosis pilaris: it is believed to be a genetic disease linked to the X chromosome, which would explain why boys are more affected. As a reminder, women have two X chromosomes while men have one X chromosome and one Y chromosome. The mutation must be carried by both X chromosomes of a woman for her to be affected by atrophying keratosis pilaris, whereas it is sufficient for it to be present on the single X chromosome of men for them to be affected.

Note : these two hypotheses are not mutually exclusive. Scientists believe it is possible that men are more often affected than women in families where heredity is linked to the X chromosome and that the disease is in other cases transmitted in an autosomal dominant manner. Finally, researchers have observed the sporadic development of atrophying keratosis pilaris in some individuals without a genetic history.

To date, treatments for atrophying keratosis pilaris are largely ineffective. Prescriptions mainly include keratolytic creams and emollients to release follicular plugs, remove excess keratin and soften the skin. Moreover, systemic retinoids such as isotretinoin and etretinate can be beneficial in the early stages of the disease as they reduce follicular hyperkeratosis and inflammation. However, they do not halt alopecia. Minoxidil, a drug typically used for alopecia, helps slow hair loss in cases of atrophying keratosis pilaris but cannot completely counter it.

• AL ABOUD K. & co. Two brothers with keratosis follicularis spinulosa decalvans. Journal of the American Academy of Dermatology (2002).

• MOHAN S. & al. Keratosis Follicularis Spinulosa Decalvans: An Uncommon Cause of Scarring Alopecia in Two Young Indian Girls. International Journal of Trichology (2013).

• SACCHIDANAND S. & others. Keratosis Follicularis Spinulosa Decalvans: A Report of Three Cases. International Journal of Trichology (2015).

• PRIYANKA J. & al. Keratosis Follicularis Spinulosa Decalvans: A Dermoscopic Perspective. Indian Journal of Paediatric Dermatology (2020).