What is Acne?

Acne is a chronic inflammatory condition of pilosebaceous units and manifests itself as comedones, papules, pustules and eventually scarring.

Epidemiology
Acne vulgaris is a common disease affecting around 40% of 16-18-year-olds. Minor degrees are an almost universal finding throughout puberty in both sexes. All races may be affected, although there is a lower incidence in Asians and blacks.

Pathology
The etiology of acne involves abnormal keratinization, hormonal activity, bacterial growth and immune hypersensitivity. The disease is limited to the pilosebaceous units of the head and upper trunk. The primary lesion arises from a change in the keratinization of the hair follicle and results in a micro-comedone due to impaction and distension of the follicle with improperly desquamated keratinocytes and sebum.
At puberty, androgens stimulate sebaceous glands to produce larger amounts of sebum, and pre-existing comedones become filled with lipids and enlarge. Propionibacterium acnes, a usually harmless commensal bacterium in the pilosebaceous units, contains bacterial lipases that convert lipid into fatty acids. Together with sebum, it causes an inflammatory response in the pilosebaceous unit resulting in the hyperkeratinization and plugging of the follicle.
The enlarging follicular lumen that contains keratin and lipid debris is known as a whitehead (closed comedone). A follicle with a port of entry at the skin with oxidized sebum forming a black tip is known as a blackhead (open comedone). The distended follicle may rupture releasing its contents into the dermis. This provokes a foreign body response resulting in papules, pustules or nodules. Scarring can follow this intense inflammation.

Clinical features
The lesions of acne vulgaris almost always occur on the face. The upper back and chest are involved in approximately 70%. The main skin lesions are comedones, both open and closed. Papules, pustules and nodules may also be present . Nodulocystic acne is a variant consisting of large tender nodules and cysts, which eventually form deep scars. It is important to recognize and treat this form of acne early in life before extensive scarring has occurred. The severity of disease can be assessed using a pictorial grading approach which looks at the extent of inflammation, range and size of inflamed lesions, and associated erythema.
A number of factors, including endocrine disorders and drugs, can exacerbate acne vulgaris.

Initial investigations
Acne is a clinical diagnosis.

Further investigations
Investigations may be required to rule out underlying causes such as hyperandrogenism and polycystic ovary syndrome.
Testosterone, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and dehydroepiandrosterone sulphate (DHEA-S) levels
In the overwhelming majority of acne patients, hormone levels are normal and, unless clinically indicated, do not need to be checked. Raised free testosterone and DHEA-S levels indicate hyperandrogenism. In polycystic ovary syndrome, the ratio of LH to FSH is increased and the levels of testosterone, oestradiol and androstenedione are raised.

Medical management
Treatment should be commenced early to prevent scarring. The choice of treatment depends on whether the acne is predominantly comedonal or inflammatory, and its severity.

Patient education
The psychological impact of acne should be assessed in each patient and therapy modified accordingly. Patients should be warned that an improvement might not be seen for at least a couple of months.

Topical preparations
Benzoyl peroxide is effective in mild to moderate acne and can be used for both comedones and inflamed lesions. Adverse effects include local skin irritation, particularly when treatment is initiated. Azelaic acid has both antimicrobial and anticomedonal properties. It is less likely to cause local irritation and may be an alternative to benzoyl peroxide.

Topical antibacterials
For mild-moderate inflammatory acne, topical antibacterials such as erythromycin and clindamycin can be used together with benzoyl peroxide. This treatment should be continued for at least 6 months before its benefits can be fully assessed. Antibacterial resistance of P. acnes has increased over the last 20 years. Failure to respond to topical treatment after 8 weeks should prompt a change of treatment.

Topical retinoids
Tretinoin and isotretinoin are effective in comedonal and inflammatory acne. Patients should be warned that some redness and peeling might occur but will settle with time. Improvement occurs over a period of months but may take longer for non-inflamed comedones.

Oral antibiotics
Systemic antibacterial treatment should be considered for all cases of moderate-severe inflammatory acne, and in cases of mild-moderate inflammatory acne where topical treatments used over a period of 3-6 months have been ineffective. Anticomedonal treatment such as benzoyl peroxide or topical retinoids can be used in conjunction with oral antibiotics. Oxytetracycline or tetracycline 500 mg twice a day is usually used. If there is no response after the first 3 months another oral antibiotic should be given. Maximum benefit usually occurs after 4-6 months. Doxycycline and minocycline both at 100 mg daily are alternative antibiotics. Erythromycin can also be used; however, there are now widespread resistant propionibacterium strains and so the response is often poor.

Hormone treatment
Co-cyprindiol (cyproterone acetate with ethinylestradiol) contains an antiandrogen that decreases sebum secretion. It is useful in women who need treatment for acne and also wish to receive oral contraception.

Oral retinoids
Isotretinoin is a synthetic retinoid that inhibits sebaceous gland function and keratinization, and also has some anti-inflammatory activity. It is extremely effective treatment for severe acne (including nodulocystic acne) and disease which has not responded to an adequate course of a systemic antibacterial. Isotretinoin, 0.5-1 mg/kg, is given for about 16 weeks. Although it has revolutionized the management of acne, it is a toxic drug that is prescribed only by, or under the supervision of, a consultant dermatologist. The drug is teratogenic and must not be given to women of child-bearing age unless they practise effective contraception. Pre-treatment tests should include a lipid profile, liver function tests, full blood count and, in the case of women, a negative pregnancy test. These tests should be repeated at 1 month and then every 3 months until the treatment is completed. Concerns have been raised that oral isotretinoin may occasionally cause depression, psychotic symptoms and rarely suicide attempts. However, retrospective studies have failed to demonstrate a relationship. Nevertheless, particular care needs to be taken in patients with a history of depression.
After successful control of disease, maintenance treatment with topical agents is essential with reintroduction of oral antibiotics if acne recurs.

Prognosis
Most cases of acne clear spontaneously by the early twenties but around 5% of cases may persist into the third decade. With the appropriate treatment 90% of patients show a 50% improvement in 3 months and an 80% improvement within 6 months, but continuous treatment may be necessary for many years.