Clinical Review - Pigmented skin disorders

Contributed by Dr Mahreen Ameen, a consultant dermatologist with an interest in tropical dermatology at Guy's and St Thomas' Hospital, London.

Eczema commonly demonstrates marked folicular accentuation
Eczema commonly demonstrates marked folicular accentuation

Section 1 Epidemiology
Disease in patients with pigmented skin can present a diagnostic challenge to the clinician because of differences in clinical presentation, as well as some dermatoses being unique to certain ethnic groups.

The changing demographics of UK urban populations are making clinicians increasingly aware of the need to recognise the manifestations of skin disease in darker skin colours and the important differences in their management.

Common diseases
One of the difficulties in diagnosing even common diseases in darker skin, such as fungal infections and eczema, is the apparent absence of erythema.

Eczema also appears entirely different in black skin, in which it commonly demonstrates marked follicular accentuation presenting with discrete small perifollicular scaly papules (see picture, right).

Scarring can be severe and disfiguring as, for example, in discoid lupus erythematosus. Darker skins are prone to increased pigmentation, not only as a consequence of skin disease, but also as a racial variant of normal skin.

Examples include melanonychia of nails (linear brown or black pigmentation of the nail plate) and racial pigmentation of the palms, soles and gingiva.

The variations in clinical presentation in darker skin are attributed to differences in the structure and function of skin fibroblasts, melanocytes and hair follicles.

Clinical services have also been affected by changing epidemiological trends in skin disease in the UK, particularly the dramatic increase in incidence of tinea capitis in African-Caribbean children in urban areas.

In childhood populations, tinea capitis and atopic eczema are the most frequent skin diseases seen. Trichophyton tonsurans is the dermatophyte most commonly incriminated in the surge of tinea capitis.

It is spread through close contact between children and African-Caribbean children in particular appear susceptible. This has also been attributed to the use of infected hair clippers, shaving of the scalp and the use of hair oils, which may act as a vehicle for spreading fungal spores between close contacts.

The British Association of Dermatologists recommends that in urban areas, any child with a scaly scalp should undergo mycology investigations.

In the case of T tonsurans, which is highly infectious, all household and close contacts should be screened.1

Among adults, acne and related conditions are most commonly seen.

Section 2 skin disorders

Keloid scars
Keloid scars are more common in black-skinned patients. They extend beyond the original site of trauma; hypertrophic scars remain localised.

Keloids can be symptomatic, patients often complain of pruritus or tenderness. Topical steroids of moderate potency can alleviate the pruritus.

Treatment of a single or a few lesions with intralesional triamcinolone (sometimes combined with surgery and mechanical compression dressing) can be successful, but the management of extensive keloids is difficult.

Carbon dioxide laser and radiotherapy are sometimes used. Keloids often recur.

Acne
The clinical presentation of acne can be different in darker skin. Post-inflammatory hyperpigmented macules are the dominant and frequent sequelae.

The hyperpigmentation is often more disfiguring for the patient than the acneiform lesions themselves, because it can take months to resolve.

Black-skinned patients are also at increased risk of scarring, including keloid scarring, which tends to affect the jaw line, chest and back. Early aggressive management of acne is advised to prevent the development of further pigmentation and avoid the risk of scarring.

This is usually associated with topical retinoids and benzoyl peroxide, which can dry the skin. These should therefore be prescribed at lower concentrations and used as tolerated.

Alternatively, retinoid analogues, such as adapalene and tazarotene, may be used - they are often better tolerated.2

Black-skinned patients may use hair pomades (oil or ointment) to improve the manageability of their hair. However, this can lead to a high incidence of 'pomade acne' or 'acne cosmetica', consisting of open and closed comedones, which particularly affects the forehead and temples, where the pomade comes into contact with the skin.

It has been reported to affect up to 70 per cent of long-term users of hair pomade.3 Such products should be avoided or only applied to the distal ends of the hair.

Ingrowing hairs
Pseudofolliculitis barbae, folliculitis decalvans and acne keloidalis nuchae are similar conditions and some patients may have the complete triad of disorders.

They are caused by ingrowing hairs in individuals with short, tightly curled hair, producing painful and pruritic papules that may develop into hypertrophic or keloidal scarring. African-Caribbean men are particularly susceptible and this is a difficult group of disorders to treat.

Pseudofolliculitis barbae affects the beard region and is exacerbated by close shaving. This causes hair to grow horizontally and produces a foreign body reaction in the skin.

The problem is improved if hair is allowed to grow for several months. Alternative methods of hair removal, such as electric shavers or depilatory creams, should be used.

Skin cancer
Although all of the common types of primary skin cancer are rare in darker skins, they can be associated with significant morbidity and mortality. This is a result of patients presenting late with advanced disease because of a lack of awareness of the risks of developing skin cancer, as well as clinicians failing to diagnose early because of a low index of suspicion in this group of patients.

In addition, there are atypical clinical presentations. Acral lentiginous melanoma, the most common form of melanoma, involves areas of skin that are not exposed to the sun, such as the palms, soles, nails and mucosal surfaces including the mouth, anus and genitalia.

It is aggressive and any pigmented lesion must be carefully assessed. In contrast to white-skinned patients, basal cell carcinomas are less common than squamous cell carcinomas and have an almost equal prevalence in this group of darker-skinned patients. Squamous cell carcinomas tend to occur on unexposed areas of skin.4,5

Differences between pigmented and white skins

  • Erythema is more difficult to detect in darker skin.
  • Lichenification from chronic scratching is more common and worse in black skin.
  • Pigmentary problems (hyper and hypopigmentation) are more common in darker skin.
  • A follicular pattern of atopic eczema is very common in black-skinned children.
  • There is a higher risk of keloid scarring in black skin.
  • Darker skin is protected from the harmful effects of UV exposure, so photoaging and skin cancer are less common.
  • In black-skinned patients, skin cancer in non-exposed sites is more common and is often more aggressive.
  • These differences are believed to be the result of differences in structure and function between different skin colours.1

Section 3 Pigmentary skin disorders
Pigmentary skin disorders are an extremely common problem that can be psychologically devastating for some patients. The darker the skin colour, the more marked the contrast between the hypoor hyperpigmentation and normal skin colour.

Hyperpigmentation is normally post-inflammatory, occurring after the resolution of atopic eczema, psoriasis, allergic or irritant contact dermatitis and acne. However, melasma is a form of non-inflammatory hyperpigmentation, and is an acquired hypermelanosis of sun-exposed areas of the face.

Hypopigmentation can also be post-inflammatory and, in black skin, it often occurs after the resolution of seborrhoeic or atopic eczema.

Some patients mistakenly believe the hypopigmentation occurs because topical steroids 'bleach' their skin, so it is important to explain the aetiology of pigmentary changes.

Any inflammatory skin disease requires good control to prevent these pigmentary sequelae. There are also distinct dermatoses characterised by hypopigmentation.

Hypopigmentary skin disorders
The incidence of vitiligo is the same in all racial groups, but is far more apparent and disfiguring in darker skin. Treatment must begin early, because a long history of vitiligo is associated with a poor prognosis in terms of likely repigmentation.

Non hair-bearing areas, such as lips and fingers, respond poorly to treatment. This consists of long courses of potent topical steroids and phototherapy. Spontaneous repigmentation can still occur in up to half of patients.

Repigmentation is usually perifollicular and some patients report that it too is disfiguring because of its patchy nature.

Patients can be referred for cosmetic camouflage; the British Red Cross provides an excellent service.

Chronic UV exposure
Idiopathic guttate hypomelanosis occurs in all skin colours but is more noticeable in darker skin. Patients have multiple, small (2-6mm), well-defined white macules that affect sun-exposed areas of the body, usually the limbs.

This occurs as a result of chronic UV exposure and it can pose a cosmetic problem which cannot be treated.

Pityriasis alba is a common condition in children but is usually only apparent in darker skin. Multiple, poorly defined, mildly hypopigmented patches occur on the face. This is a mild variant of atopic eczema and the resulting post-inflammatory hypopigmentation is what is usually seen. The active stage should be managed with emollients and weak topical steroids.

It becomes more prominent in the summer as normal skin tans, so sun avoidance or a sunscreen are advisable. The skin will repigment as long as the eczema is controlled.

Pityriasis versicolor produces hyperor hypopigmented scaly lesions. After eradication of the causative yeast, dark skins often develop post-inflammatory hyperor hypopigmentation.

Post-inflammatory hypopigmentation usually repigments with sun exposure; post-inflammatory hyperpigmentation can take months to resolve.

Treatment
Treatment of hyperpigmentation is difficult and the goal is to reduce it without producing hypopigmentation or irritation of the surrounding skin, which can cause further post-inflammatory hyperpigmentation.

The most effective and commonly used agent is hydroquinone, which acts by inhibiting melanin production. Concentrations of 3-5% are effective. Higher concentrations are associated with adverse effects, including irritation. Concomitant use of 1% hydrocortisone minimises this.

Hydroquinone can also cause hypopigmentation of skin surrounding the treatment area, although this usually resolves following discontinuation of treatment. It is often combined with an alpha-hydroxy acid or retinoid to increase penetration and enhance efficacy.

One widely used depigmenting solution contains a triple formulation of hydroquinone, hydrocortisone and tretinoin.

Other topical treatments include azelaic acid and kojic acid, which are not associated with significant irritation.

Sun exposure will reverse the effects of treatment, so sun avoidance and protection are critical.6 The Q-switched ruby laser has been successfully used to treat post-inflammatory hyperpigmentation.

Section 4 Hair disorders
Hair loss or alopecia is a common condition that can cause cosmetic and psychological problems. Its aetiology varies among racial groups and hairstyling practices are often the cause.

Thermal or chemical straightening, braiding and weaving can all traumatise the hair and lead to problems such as traction alopecia. This is caused by pulling forces being applied to the hair and particularly affects the frontotemporal hairline.

Centrifugal cicatricial alopecia, an uncommon condition affecting African-Caribbean women, produces baldness at the vertex of the scalp (see picture, right), while in trichorrhexis nodosa, the hair is weakened and breaks easily. These problems may be irreversible, so early intervention is critical.

Management involves changing hairstyling practice. Some patients may want to consider hair replacement surgery.

Seborrhoeic dermatitis is a common problem, especially in African-Caribbean women. It is often associated with infrequent hair washing, practised because of the particular hairstyles worn.

In addition, products used for styling hair can have a drying effect, especially those including lanolin derivatives, which can worsen this condition.7

Resources
1. Higgins EM, Fuller LC, Smith CH. Guidelines for the management of tinea capitis. Br J Dermatol 2000; 143(1): 53-8.

2. Taylor SC, Cook-Bolden F, Rahman Z et al. Acne vulgaris in skin of color. J Am Acad Dermatol 2002; 46(2 Suppl Understanding): S98-106.

3. Plewig G, Fulton JE, Kligman AM. Pomade acne. Arch Dermatol 1970; 101: 580-4.

4. Bang KM, Halder RM, White JE et al. Skin cancer in black Americans: a review of 126 cases. J Natl Med Assoc 1987; 79(1): 51-8.

5. Byrd-Miles K, Toombs EL, Peck GL. Skin cancer in individuals of African, Asian, Latin-American and American-Indian descent: differences in incidence, clinical presentation, and survival compared to Caucasians. J Drugs Dermatol 2007; 6(1): 10-16.

6. Halder RM, Richards GM. Topical agents used in the management of hyperpigmentation. Skin Therapy Lett 2004; 9(6): 1-3.

7. Callender VD, McMichael AJ, Cohen GF. Medical and surgical therapies for alopecias in black women. Dermatol Ther 2004; 17(2): 164-76.

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