Keratosis pilaris is an extremely common dermatosis that in mild states can be considered a variant of normal skin. It is usually brought to the clinician’s attention as an afterthought, or the clinician observes the condition and tells the patient about it for educational purposes. There are more severe forms of keratosis pilaris in which patients present to the dermatologist for therapy. Many distinct variants of keratosis pilaris exist, and they are named based on area of involvement.
Clinical Findings: Keratosis pilaris is one of the most common dermatoses and is thought by some to be a variant of normal. It is found in more than 40% of the adult population and in as many as 80% of children. There is no sex or race predilection. It typically begins soon after a child reaches 5 years of age. Most cases are asymptomatic and are of no concern to the patient or of only cosmetic concern. The upper lateral arms are the most common site of involvement. Small (1-2 mm), pink-to-red follicular hyperkeratotic papules are present to a varying extent. Some are so fine that they are noticeable only on palpation. Other cases are more widespread and can include the upper thighs, shoulders, and cheeks. Widespread cases tend to be more noticeable, and the small papules tend to be more inflammatory in nature.
This inflammatory form of keratosis pilaris is also called keratosis pilaris rubra. It is typically manifested by bright red, small, hyperkeratotic papules that may resemble pustules. They can be mistaken for acneiform lesions. A small scraping of the inflammatory lesion results in removal of a small keratin plug rather than the contents of an acneiform pustule. The location on the outer arms and upper thighs also helps to differentiate this condition from acne. Both keratosis pilaris and acne are extremely common, and they are frequently seen together in the same patient.
Ulerythema ophryogenes is a keratosis pilaris variant that manifests in early childhood. The lateral one third of the eyebrow is affected with minute, red keratotic papules. Hair loss of the lateral eyebrows is common. The rash may affect other parts of the face and may heal with tiny pitted scars. It is almost always seen along with keratosis pilaris. Over time, alopecia may develop in the affected regions, especially the lateral eyebrows.
Atrophoderma vermiculata is one of the rarest of the keratosis pilaris variants. It manifests as small, hyperkeratotic plugs on the cheeks that resolve and leave behind small, atrophic scars in a fine mesh-like pattern. Erythromelanosis follicularis faciei et colli is similar in nature to atrophoderma vermiculata, but it lacks any evidence of scarring. This condition has been reported to occur most commonly in young men during the second and third decades of life. Postinflammatory hyperpigmentation is another unusual feature not seen with the other variants.
Keratosis follicularis spinulosa decalvans is probably the least common keratosis pilaris variant. It is inherited in a X-linked fashion and thus affects males. It is manifested by areas of skin thickening and follicular plugging along with areas of scarring alopecia. This condition may also affect the eyelashes. Corneal dystrophy and blepharitis can be seen.
Pathogenesis: The exact etiology of keratosis pilaris is unknown. It is believed to be caused by an abnormality in follicular keratinization of the infundibulum.
Histology: Keratosis pilaris is rarely biopsied. A keratin plug is the most prominent feature. The plug is typically 1 to 2 mm in diameter and may lie on top of a meager lymphocytic infiltrate.
Treatment: No therapy is required for most cases. A keratolytic moisturizer or humectant moisturizer works well. These include lactic acid and salicylic acid based moisturizers. After discontinuation, however, the rash of keratosis pilaris returns over a period of a few weeks to months. Many other therapies have been used. Vitamin A derivatives (e.g., tretinoin) are among the more commonly used prescription medications. The cream is applied daily and has been successful in removing the redness and hyperkeratosis.