The clinical type of comedo could, and perhaps should, influence the treatment prescribed.
Biopsy sections of normal-looking skin in an acne-prone individual with comedonal acne will frequently (28%) show histological features of microcomedones. Biopsies of papules taken at up to 72 h of development will reveal a microcomedone in 52% of subjects, a whitehead in 22% and a blackhead in 10% , confirming even further the practical need to apply topical therapies to apparently non-involved skin.
Dermatologists recognise the typical pattern of comedones seen in clinical practice, and so this requires no further explanation.
In all patients, it is essential to stretch the skin, using a good light, at a shallow angle, otherwise even ordinary comedones will not be recognised. Stretching of the skin will demonstrate, in about 20% of patients, comedones which would otherwise not be seen, and thus prevent the prescription of inappropriate topical therapy. Our treatment protocols for ordinary, missed and microcomedones are similar. The topical treatment must be applied not just to the lesions, but also to the adjacent subclinically 'normal' skin. Physical methods of therapy such as blackhead removers are worthy of consideration in a small number of patients with obvious blackheads. Topical retinoids are the most effective topical therapy [16-18, 23-25].
Patients with these comedones represent a difficult subgroup who present with predominantly very small, almost confluent closed comedones giving the feel of 'sandpaper' which may become inflamed. They are particularly seen on the forehead and are difficult to treat. On the whole, they show little or varied response to oral antibiotics and topical retinoids, and the optimum treatment is oral isotretinoin at a preferred dosage of 0.5 mg/kg/ day.
These are also easily missed (fig. 4), and therefore there is a need to stretch the skin. They infrequently present as a focus of continued inflammation. They are
surprisingly quite large and may reach a size of up to 1 cm. Treatment is difficult, and the optimum therapy is probably focal cautery using a technique described later in this review for the treatment of macrocomedones, which allows the drainage of retained corneocytes. Such a technique is successful in about 50% of submarine comedones.
This term refers to blackheads and whiteheads which are > 1 mm in size. Whiteheads are the most common. They need to be treated for two reasons. They are a cosmetic problem and may flare into inflamed lesions (fig. 5), especially in patients treated with oral isotretinoin. In such patients, they are the major reason for a severe flare of the acne and surprisingly are easily missed unless adequate lighting and examination techniques, i.e. stretching the skin, are used. The optimum therapy is gentle cautery [26-28]. This is performed under topical local anaesthesia using an anaesthetic cream such as EMLA® which is applied for 60-75 min under an occlusive dressing such as Tegaderm®. The area is then lightly touched with a small hot-wire cautery probe, the tip being grey in colour rather than vividly red and red-hot. The purpose is not to burn the skin significantly but to produce low-grade, localised thermal damage. This therapy is far superior to topical retinoids: at 2 weeks of treatment using light cautery there is typically virtually 100% clearance compared with topical retinoids which produce a reduction in the order of < 10% . Not all patients respond perfectly. A test area is always treated initially, and thereafter the remaining lesions are treated in further sessions. Five percent develop recurrent lesions requiring multiple treatments with gentle cautery. Scarring and pigmentary changes are uncommon. If the patient has macrocomedones and is on oral isotretinoin and the acne flares, it is necessary to stop the oral isotretinoin, consider giving oral steroids and treat the macrocomedones. Macrocomedones are also a cause of a slow and poor response to oral isotretinoin therapy .
These may be due to corticosteroids [29, 30] or anabolic steroids [31, 32] and 'blue comedones' can occur, albeit very infrequently, due to minocycline-induced pigmentation. Treatment of drug-induced comedones is by removal of the cause and by treating with either topical retinoids or gentle cautery.
This is a clinical event seen particularly in Afro-Carib-beans who apply hair preparations to defrizz their hair. Many whiteheads (fig. 6) are frequently seen, and these may evolve into inflammatory lesions. Treatment in-
eludes stopping the hair preparations, topical retinoids and possibly oral antibiotics.
This is also characterised by many comedones [33-36]. Indeed, comedonal acne is a hallmark of this disease (fig. 7), and inflammatory lesions are less frequent. Inflamed lesions may be treated with oral or topical benzoyl peroxide or antibiotics. Gentle cautery is very successful; there is usually a poor response to topical and oral reti-noids .
These are rare and may present before puberty but more often at and around puberty [37, 38]. The lesions may be typical confluent comedones (fig. 8) or white-heads, usually occurring asymmetrically. They may be localised or, in some unfortunate individuals, extremely extensive. Treatment is difficult. Response to oral and topical retinoids is unsatisfactory. Physical methods are also unsatisfactory, but gentle cautery, excision of locally affected areas and carbon dioxide laser therapy can be tried; however, as yet there seems to be no satisfactory solution for the majority of patients.
Patients with conglobate comedones are predominantly males with extensive truncal acne characterised by severe nodular inflammation and scarring. A hallmark of the disease is grouped comedones [40, 41], particularly on the posterior neck and upper trunk. The comedones may be blackheads, whiteheads or both. This is a really difficult subgroup to treat. There are no satisfactory data to demonstrate which is the preferred way of treating such comedones.
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