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 (
).
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 KP that fails to respond to emollients and keratolytics.
介紹
毛周角化症（KP）是一種常見的毛囊角化異常疾病，其特徵是出現角化性毛囊丘疹，伴隨程度不一的毛囊周圍紅斑。皮損主要涉及上臂近端、大腿和臉頰的伸側（圖1A-C）。毛週角化症常與異位性皮膚炎及尋常型魚鱗病並存[ 1,2 ]。
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 [
1,2].
流行病學
KP通常發生於兒童或青少年，無性別差異。所有種族群體均可見KP，據估計，兒童族群的盛行率為2%至12%
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
病因和發病機制
毛周角化症 (KP) 的病因尚未完全明確，但與絲聚蛋白基因突變有關 [ 6,7 ]。它被認為是一種遺傳性角化障礙，導致毛囊口形成角質栓。其遺傳模式尚未確定，但在許多情況下符合體染色體顯性遺傳模式，且具有不完全外顯率。研究發現，全身型 KP 患者存在 18p 染色體缺失 [ 8,9 ]。有少數報告稱，尼洛替尼（一種核准用於治療伊馬替尼抗藥性慢性骨髓性白血病的第二代酪胺酸激酶抑制劑）可誘發 KP
ETIOLOGY AND PATHOGENESIS
The cause of KP is not fully understood, but it has been associated with filaggrin mutations [
6,7]. 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 [
8,9]. 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
病理
角化過度形成的角質栓，可能包含一根或多根扭曲的毛髮，填充並擴張毛囊漏斗部，並突出於皮膚表面（圖2）。真皮上層可能出現輕度血管周圍淋巴球浸潤
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 [
14].
臨床表現
典型表現 － 毛周角化症通常在兒童期或青春期發病，但也可能發生於嬰兒（圖3）[ 15 ]。其主要表現為棘狀角化性丘疹，多見於上臂和大腿近端伸側（圖1B和圖1C）。臉部、軀幹、臀部和四肢遠端也可能受影響（圖1A-D）。丘疹可成簇或散在分佈，常伴隨輕度毛囊周圍紅斑。
CLINICAL MANIFESTATIONS
Typical findings — KP typically manifests during childhood or adolescence but may also occur in infants (
picture 3) [
15]. It presents with spiny keratotic papules predominantly involving the extensor aspects of the proximal arms and thighs (
picture 1B and
picture 1C). 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.
毛周角化症通常無症狀，可能在身體檢查時偶然發現。部分患者會感覺皮膚粗糙，外觀不佳。由於毛週角化症常與其他皮膚疾病有關，例如異位性皮膚炎或尋常型魚鱗病，因此這些疾病也可能出現在患者的皮膚上。
冬季病情加重較為常見，可能是由於皮膚乾燥或厚衣物摩擦所致[ 16 ]。也有報告指出妊娠期病情會加重（圖4）[ 17 ]。毛周角化症通常會隨著年齡增長而改善，但也可能持續到成年[ 16 ]。
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 [
16]. Worsening during pregnancy has also been reported (
picture 4) [
17]. KP usually improves with age but may persist into adult life [
16].
臨床變異型 － 在某些患者中，毛囊周圍紅斑可能很明顯，尤其是在臉頰、前額和頸部（圖 5和圖 6A）。這種類型的毛周角化症稱為「毛週紅角化症」[ 18 ]。
「臉部和頸部毛囊紅斑黑變病」是另一種KP變異型，主要見於青少年和青年。其臨床表現為太陽穴和臉頰出現紅斑、色素沉澱和毛囊性丘疹，並可延伸至耳前區和頸側（圖6B）[ 19,20 ]。與單純性KP類似，毛囊性角化性丘疹常出現於手臂伸側。
Clinical variants — In some patients, perifollicular erythema may be prominent, particularly on the cheeks, forehead, and neck (
picture 5 and
picture 6A). This form of KP is called "keratosis pilaris rubra" [
18].
"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 6B) [
19,20]. Follicular keratotic papules, similar to simple KP, are often found on the extensor aspects of the arms.
相關疾病 － 毛周角化症常見於尋常型魚鱗病和異位性皮膚炎患者[ 21 ]。也有報告指出與第1型糖尿病[ 22 ]和肥胖[ 23,24 ]有關。Associated conditions — KP is commonly seen in patients with ichthyosis vulgaris and atopic dermatitis [
21]. It is also reported in association with type 1 diabetes mellitus [
22] and obesity [
23,24].
診斷
毛周角化症的診斷主要依據臨床表現，即在近端手臂和大腿伸側發現棘狀角化性丘疹，伴隨不同程度的紅斑（圖1A-C）。若涉及眉毛、發炎明顯、出現萎縮性疤痕且伴隨掉髮，則提示萎縮性毛周角化症的診斷。
通常無需進行活檢；如果進行活檢，則會顯示毛囊漏斗部擴張和角化過度形成的角蛋白栓。
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.
治療
隨著年齡增長，毛周角化症（KP）可能會自行改善，許多情況下無需治療。然而，對於存在大面積毛周角化症和/或嚴重紅斑，且有美容顧慮的患者，他們可能會要求治療以減輕皮膚粗糙和紅斑。改善通常是暫時的；對治療有效的患者應接受指導，以繼續治療並維持緩解。
所有患有毛周角化症的患者都可以透過採取皮膚護理措施來防止皮膚過度乾燥，包括使用溫和的肥皂或無皂清潔劑，以及避免熱水浴或淋浴。
●潤膚劑和角質溶解劑－潤膚劑和外用角質溶解劑是治療毛周角化症的第一線療法。含有乳酸、水楊酸或外用尿素的製劑有助於軟化和撫平角化丘疹，但不能減輕或緩解相關的紅斑[ 1,29 ]。在一項納入30例毛周角化症患者的研究中，將含有20%尿素的保濕霜塗抹於患處四周，可有效改善皮膚質地和外觀[ 30 ]。
●外用維他命A酸類藥物－對於使用潤膚劑和角質溶解劑無效的患者，可使用外用維他命A酸類藥物（例如，0.05%維他命A酸乳膏、 0.1%阿達帕林乳膏或0.05%他扎羅汀乳膏）。外用維他命A酸類藥物每日一次，療程為8至12週。在一項小型隨機試驗中，0.05%他扎羅汀乳膏在減輕上臂後側超過20個角化過度性丘疹患者的瘙癢、粗糙和發紅方面比安慰劑更有效[ 31 ]。在一項小型開放性研究中，0.01%他扎羅汀乳劑在4至8週內減輕或消除了角化過度性丘疹病變[ 32 ]。
●局部皮質類固醇－若發炎明顯，可短期使用低至中等效力的局部皮質類固醇（表1中的第4至6組）與其他局部用藥合併使用[ 33 ]。局部皮質類固醇每日塗抹於患處1至2次，療程1至2週。
●其他療法－其他療法包括全身性維他命A酸類藥物、雷射療法[ 34 ]或其他剝脫性手術。有些患者嘗試了雷射（例如，脈衝染料雷射、長脈衝755 nm翠綠寶石雷射、810 nm長脈衝二極體雷射、長脈衝1064 nm釹摻雜釔鋁石榴石[Nd:YAG]雷射）聯合微晶磨皮術，結果顯示毛囊紅斑和皮膚粗糙度暫時減輕[ 35-38 ]。
TREATMENTKP may improve spontaneously with age and, in many cases, does not require treatment. 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 continue therapy to maintain remission.
All patients with KP may benefit from skin care measures to prevent excessive skin dryness, including using mild soaps or soap-free cleansers and avoiding hot baths or showers.
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 [
1,29]. In a series of 30 patients with KP, a moisturizer cream containing 20% urea applied to the involved skin for four 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 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 [
33]. Topical corticosteroids are applied to the involved areas once or twice daily for one to two weeks.
●Other therapies – Other therapies include systemic retinoids, laser therapy [
34], 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
還蠻多醫師都有寫此病的中文衛教文章. 下面全文轉貼
毛孔角化症(keratosis pilaris) 北市聯醫 皮膚科 許智恭醫師炎熱的夏季來臨，大家紛紛換穿短袖的衣服，涼爽透氣的短褲。此時有 相當可觀的人卻長期受到一種常見的皮膚問題困擾，雖然不常造成搔癢疼痛的不適症狀，可是因為呈現不怎麼整潔雅觀的樣貌，想努力洗刷這些不太美觀的皮膚疹子 卻總是令人失望。這種發生在側臉部與頸部、手臂外側、腿部外側，呈現許多密集的毛孔突起粗糙小顆粒，顏色有灰、黑、紅等不同色澤的病變，有些人俗稱雞皮疙 瘩，正式的醫學名稱是「毛孔角化症」keratosis pilaris。
「毛孔角化症」是種常見的皮膚問題，無論在皮膚診療室或是日常生活中都很容易看到這類情形，特別是年輕人。研究統計顯示約有半數的人在十歲以前開始發 生，到了十幾歲的青年期有高達50%~80%的人表現出毛孔角化症的病徵，男女比例相當，有家族遺傳史的佔30%~50%左右，隨著年紀增長，大概有ㄧ半 的人會逐漸好轉，可是角化症存在的時間長達20年以上。如果病情加劇或是因出汗或摩擦刺激而產生紅腫發癢的情形，仍需要接受治療。冬季常見深色突起的毛孔 顆粒更加明顯，夏季雖然角化有緩和傾向，但是紅癢的症狀反而增多，同時因為穿著短袖衣服容易看到變化部位，尋求治療的意願反而提高。
大部分的患者身體健康，有少部分人併有魚鱗癬、乾皮症等角質異常病症，其他有異位性皮膚炎、過敏性鼻炎、氣喘的異位性體質，惟可能只是共存的病症，無 直接因果關聯。毛孔角化症好發於臉頰側面、手臂外側、大腿前外側，嚴重的在頸部、背上、臀部、小腿都可看見。外觀上在毛孔開口處可見黑而硬的角化顆粒，凸 出於皮表面，周圍有時可見輕微的發紅現象，尤其是在臉頰側面，特稱「紅色毛孔角化症」。檢查阻塞的毛孔內偶而可見黑色的細毛陷在裡面。這種變化與青春痘的 粉刺有些相似但是原因與特徵均不同，可請教醫師分辨出來。
治療上要強調刻意強力清潔或用刷子、粗布摩擦表面會導致發炎紅腫，進而演變成發炎後色素沉積，但卻是ㄧ般人最常想到的作法，應記取前人的失敗經驗，避 免ㄧ再重複犯錯。外用角質軟化劑、外用A酸(retinoid)藥膏、發炎抑制劑、果酸煥膚治療、脈衝式染料雷射(PDL)、釹雅克雷射(Nd:YAG laser)眾多藥品與醫療科技選擇須在專業皮膚科醫師的協助下才能得到理想的療效，這正是美容醫學有所發揮，達成提升生活品質，促進身心健康印象的目 標。
