Pathogenesis

Lesions of acne vulgaris develop in sebaceous follicles, which consist of large, multilobular sebaceous glands that drain their products into the follicular canals. The initial lesion of acne is a microcomedone, which progresses to a comedone. A comedone is a dilated epithelium-lined follicular sac filled with lamellated keratinous material, lipid, and bacteria. An open comedone, known as a blackhead, has a patulous pilosebaceous orifice that permits visualization of the plug. An open comedone becomes inflammatory less commonly than does a closed comedone or whitehead, which has only a pinpoint opening. An inflammatory papule or nodule develops from a comedone that has ruptured and extruded its follicular contents into the subadjacent dermis, inducing a neutrophilic inflammatory response. If the inflammatory reaction is close to the surface, a papule or pustule develops. If the inflammatory infiltrate develops deeper in the dermis, a nodule forms. Suppuration and an occasional giant cell reaction to the keratin and hair are the cause of nodulocystic lesions. These are not true cysts but liquefied masses of inflammatory debris.

The primary pathogenetic alterations in acne are (1) abnormal keratinization of the follicular epithelium, resulting in impaction of keratinized cells within the follicular lumen; (2) increased sebaceous gland production of sebum; (3) proliferation of Propionibacterium acnes within the follicle; and (4) inflammation. Comedonal acne (Fig. 661-1), particularly of the central face, is frequently the first sign of pubertal maturation. At puberty, the sebaceus gland enlarges and sebum production increases in response to the increased activities of androgens of primarily adrenal origin. Most patients with acne do not have endocrine abnormalities. Hyperresponsiveness of the sebocyte to androgens is likely involved in determining the severity of acne in a given individual. Sebocytes and follicular keratinocytes contain 5α-reductase and 3β- and 17β-hydroxyl-steroid dehydrogenase, which are capable of metabolizing androgens. A significant number of women with acne (25-50%), particularly those with relatively mild papulopustular acne, note that their acne flares about 1 wk before menstruation.

Figure 661-1 Primarily comedonal acne in a 7 yr old girl.

Freshly formed sebum consists of a mixture of triglycerides, wax esters, squalene, and sterol esters. Normal follicular bacteria produce lipases that hydrolyze sebum triglycerides to free fatty acids. Those of medium-chain length (C8-C14) may be provocative factors in initiating an inflammatory reaction. Sebum also provides a favorable substrate for proliferation of bacteria. P. acnes appears to be largely responsible for the formation of free fatty acids. Skin surface P. acnes counts do not correlate with the severity of acne. There is a correlation between reduction of P. acnes count and improvement in acne vulgaris. It is probable that bacterial proteases, hyaluronidases, and hydrolytic enzymes produce biologically active extracellular materials that increase the permeability of the follicular epithelium. Chemotactic factors released by the intrafollicular bacteria attract neutrophils and monocytes. Lysosomal enzymes from the neutrophils, released in the process of phagocytizing the bacteria, further disrupt the integrity of the follicular wall and intensify the inflammatory reaction.

Clinical Manifestations

Acne vulgaris is characterized by 4 basic types of lesions: open and closed comedones, papules, pustules (Fig. 661-2), and nodulocystic lesions (Fig. 661-3 and Table 661-1). One or more types of lesions may predominate. In its mildest form, which is often seen early in adolescence, lesions are limited to comedones on the central area of the face. Lesions may also involve the chest, upper back, and deltoid areas. A predominance of lesions on the forehead, particularly closed comedones, is often attributable to prolonged use of greasy hair preparations (pomade acne) (Fig. 661-4). Marked involvement on the trunk is most often seen in males. Lesions often heal with temporary postinflammatory erythema and hyperpigmentation. Pitted, atrophic, or hypertrophic scars may be interspersed, depending on the severity, depth, and chronicity of the process. Diagnosis of acne is rarely difficult, although flat warts, folliculitis, and other types of acne may be confused with acne vulgaris.

Figure 661-2 Inflammatory papules and pustules.

Figure 661-3 Severe nodulocystic acne.

Table 661-1 CLASSIFICATION OF ACNE

From James WD: Clinical practice: acne, N Engl J Med 352:1463–1472, 2005.

Figure 661-4 Pomade acne along the hairline.

Treatment

No evidence shows that early treatment, with the exception of isotretinoin, alters the course of acne. Acne can be controlled and severe scarring prevented by judicious maintenance therapy that is continued until the disease process has abated spontaneously. Therapy must be individualized and aimed at preventing microcomedone formation through reduction of follicular hyperkeratosis, sebum production, the P. acnes population in follicular orifices, and free fatty acid production. Initial control takes at least 6-8 wk, depending on the severity of the acne (Table 661-2 and Fig 661-5). It is also important to address the potentially severe emotional impact of acne on adolescents.

Figure 661-5 Acne treatment algorithm, BPO, benzoyl peroxide.

(From Thiboutot D, Gollnick H; Global Alliance to Improve Acne, et al: New insights into the management of acne: an update from the global alliance to improve outcomes in acne, J Am Acad Dermatol 60:S1–S50, 2009.)

The pediatrician must be aware of the frequently poor correlation between acne severity and psychosocial impact, particularly in adolescents. As adolescents become preoccupied with their appearance, offering treatment even to the youngster whose acne is mild may enhance self-image.