Keratosis pilaris

INTRODUCTION — Keratosis pilaris (KP) is a common disorder of follicular keratinization characterized by keratotic follicular papules with variable perifollicular erythema. Lesions involve predominantly the extensor aspects of proximal arms, thighs, and cheeks (picture 1A-C). KP is often seen in association with atopic dermatitis and ichthyosis vulgaris [1].

This topic will review KP. Keratosis pilaris atrophicans and other follicular keratotic syndromes are discussed separately.

●(See "Keratosis pilaris atrophicans".)

●(See "Lichen planopilaris".)

●(See "Pityriasis rubra pilaris: Pathogenesis, clinical manifestations, and diagnosis".)

●(See "Darier disease".)

EPIDEMIOLOGY — Onset of KP typically occurs in children or adolescents without sex predilection. It is seen in all ethnic groups, with an estimated prevalence of 2 to 12 percent in pediatric populations [2-4].

ETIOLOGY AND PATHOGENESIS — The cause of KP is not fully understood but has been associated with filaggrin mutations [5,6]. It is thought to be a genetic disorder of keratinization that results in the formation of horny plugs in the hair follicle orifices. The mode of inheritance has not been determined, although in many cases it fits into an autosomal dominant pattern with incomplete penetrance. Patients with a generalized form of KP have been found to have a chromosome 18p deletion [7,8]. There are a few reports of KP induced by nilotinib, a second-generation tyrosine kinase inhibitor approved for the treatment of imatinib-resistant chronic myeloid leukemia [9-12].

PATHOLOGY — An orthokeratotic keratin plug, which may contain one or more twisted hairs, fills and dilates the infundibulum of the hair follicle and protrudes above the skin surface (picture 2). There may be a mild perivascular lymphocytic infiltrate in the upper dermis [13].

CLINICAL MANIFESTATIONS — KP typically manifests during childhood or adolescence but may also occur in infants (picture 3) [14]. It presents with spiny keratotic papules predominantly involving the extensor aspects of proximal arms and thighs. The face, trunk, buttocks, and distal extremities may also be affected (picture 1A-D). The papules may be grouped or scattered, and there is often an associated mild perifollicular erythema.

KP is usually asymptomatic and may be an incidental finding during physical examination. Some patients report a rough texture and an unsightly appearance of their skin. Since KP is associated with other skin conditions, such as atopic dermatitis or ichthyosis vulgaris, these conditions may also be seen on the patient's skin.

Exacerbation during the winter months is common, likely due to xerosis or friction from thick clothing [15]. Worsening during pregnancy has also been reported (picture 4) [16]. KP usually improves with age but may persist into adult life [15].

Clinical variants — In some patients, perifollicular erythema may be prominent, particularly on the cheeks, forehead, and neck (picture 5A). This form of KP is called "keratosis pilaris rubra" [17].

"Erythromelanosis follicularis faciei et colli" is another variant of KP, primarily seen in adolescents and young adults. It presents with erythema, hyperpigmentation, and follicular papules involving the temples and cheeks with extension to the preauricular areas and sides of the neck (picture 5B) [18,19]. Follicular keratotic papules, similar to simple KP, are often found on the extensor aspects of the arms.

Associated conditions — KP is commonly seen in patients with ichthyosis vulgaris and atopic dermatitis [20]. It is also reported in association with type 1 diabetes mellitus [21] and obesity [22,23]. (See "Atopic dermatitis (eczema): Pathogenesis, clinical manifestations, and diagnosis" and "Ichthyosis vulgaris".)

DIAGNOSIS — The diagnosis of KP is clinical, based upon the finding of spiny keratotic papules with variable erythema involving the extensor aspects of proximal arms and thighs (picture 1A-C). Involvement of the eyebrows, marked inflammation, and atrophic scarring with alopecia suggest the diagnosis of KP atrophicans.

Biopsy is usually not necessary; if performed, it reveals a dilated follicular infundibulum and an orthokeratotic keratin plug. (See 'Pathology' above.)

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of KP includes:

●Lichen spinulosus – Lichen spinulosus is typically only seen in pediatric patients and is characterized by small, follicular papules with keratotic spines that coalesce into larger patches distributed symmetrically on the trunk and extremities (picture 6). Lichen spinulosus typically spontaneously remits [24].

●Phrynoderma – Phrynoderma is characterized by follicular hyperkeratosis, with papules first appearing on the extensor surfaces on the extremities, shoulders, and buttocks (picture 7). It is caused by vitamin A deficiency or general malnutrition [25]. (See "Overview of vitamin A", section on 'Deficiency'.)

●Keratosis pilaris atrophicans – Keratosis pilaris atrophicans is a group of rare genodermatoses characterized by follicular keratosis, a variable degree of inflammation and secondary scarring, and/or alopecia [26]. They include keratosis pilaris atrophicans faciei (also called ulerythema ophryogenes), atrophoderma vermiculatum, and keratosis follicularis spinulosa decalvans. The face and in particular the lateral eyebrows and cheeks are typically involved (picture 8A-C) [27]. (See "Keratosis pilaris atrophicans".)

Follicular keratosis is also seen in Darier disease (picture 9A-B) and perforating dermatoses (picture 10) disease. However, their clinical presentation is remarkably different from KP [1]. (See "Darier disease".)

TREATMENT — KP may improve with age without treatment; however, it very commonly waxes and wanes throughout one's lifetime into early and middle adulthood. It is, however, less commonly seen in older patients. However, patients with widespread KP and/or intense erythema who have cosmetic concerns may request treatment to reduce skin roughness and erythema. Improvement is usually temporary; responsive patients should be educated to maintain therapy to achieve continued remission.

All patients with KP may benefit from skin care measures aimed at preventing excessive skin dryness, including using mild soaps or soap-free cleansers and avoiding hot baths or showers [28]:

●Emollients and keratolytics – Emollients and topical keratolytics are the first-line therapy for KP. Preparations containing lactic acid, salicylic acid, or topical urea are helpful in softening and flattening the keratotic papules, but do not reduce or relieve the associated erythema [29]. In a series of 30 patients with widespread KP, a preparation of salicylic acid 2% in topical urea cream 20% applied to the involved skin for several weeks was effective in improving the skin texture and appearance [30].

●Topical retinoids – Topical retinoids (eg, tretinoin 0.05% cream, adapalene 0.1% cream, or tazarotene 0.05% cream) may be used as a second-line therapy for patients who fail to respond to emollients and keratolytics. Topical retinoids are applied once a day for 8 to 12 weeks. In a small, randomized trial, tazarotene 0.05% cream was more effective than placebo in reducing itching, roughness, and redness in patients with more than 20 hyperkeratotic papules on the posterior upper arms [31]. In a small, open study, tazarotene 0.01% emulsion reduced or resolved KP lesions in four to eight weeks [32].

●Topical corticosteroids – Short courses of low- to medium-potency topical corticosteroids (groups 4 to 6 (table 1)) may be used in conjunction with other topical agents if there is prominent inflammation [30]. Topical corticosteroids are applied to the involved areas once or twice daily for one to two weeks.

●Other therapies – Third-line therapies include systemic retinoids, laser therapy [33], or other ablative procedures. Combination treatments with lasers (eg, pulsed dye laser, long-pulsed 755 nm alexandrite laser, 810 nm long-pulsed diode laser, long-pulsed 1064 nm neodymium-doped yttrium aluminum garnet [Nd:YAG] laser) and microdermabrasion have been tried in a few patients with temporary reduction of perifollicular erythema and skin roughness [34-37]. (See "Light-based, adjunctive, and other therapies for acne vulgaris", section on 'Microdermabrasion'.)

SUMMARY AND RECOMMENDATIONS

●Clinical presentation – Keratosis pilaris (KP) is a common disorder of follicular keratinization. It typically appears during childhood or adolescence with spiny, keratotic papules (picture 1C) predominantly involving the extensor aspects of proximal arms and thighs (picture 1A). The face, trunk, buttocks, and distal extremities may also be affected. Variants with prominent background erythema have been described (picture 5A-B). KP is often seen in association with atopic dermatitis and ichthyosis vulgaris. (See 'Clinical manifestations' above and 'Clinical variants' above and 'Associated conditions' above.)

●Diagnosis – The diagnosis of KP is clinical, based on clinical features. Involvement of the eyebrows, marked inflammation, and atrophic scarring with alopecia suggest the diagnosis of keratosis pilaris atrophicans (picture 8A-C). (See 'Diagnosis' above and 'Differential diagnosis' above and "Keratosis pilaris atrophicans".)

●Management – KP typically improves with age without treatment. However, for patients with widespread KP who have cosmetic concerns, treatment with emollients and topical keratolytics can provide symptomatic relief. Topical retinoids (eg, tretinoin 0.05% cream, adapalene 0.1% cream, or tazarotene 0.05% cream) are a second-line therapy for patients who fail to respond to emollients and keratolytics. (See 'Treatment' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Jennifer Perryman, MD, who contributed to an earlier version of this topic review.