Pityriasis amiantacea

What is pityriasis amiantacea?

Pityriasis amiantacea is a condition in which there is excessive scaling of the scalp. Thick silvery or yellowish scales encircle the hair shafts and may bind down tufts of hair.

The scales may resemble asbestos, giving rise to the term amiantacea – the French word for asbestos is 'amiante'.

What is the cause of pityriasis amiantacea?

Pityriasis amiantacea is a reaction pattern rather than a specific diagnosis. Common conditions that may present with pityriasis amiantacea include:

• Scalp psoriasis
• Seborrhoeic dermatitis
• Atopic dermatitis
• Tinea capitis.

Head lice and lichen simplex should also be considered.

When no underlying cause is found, the condition is often called idiopathic pityriasis amiantacea.

Clinical features

Pityriasis amiantacea more often affects females than males. It is generally seen in children and young adults.

It is characterised by thick scales wrapping around and binding down tufts of hair. The scaling may be localised or generalised depending on the underlying condition and its duration.

It may be complicated by secondary staphylococccal infection (impetiginisation), when the skin becomes sticky, oozy and crusted. Temporary or permanent hair loss (alopecia) may also occur.

If the underlying skin condition is not clear, the entire skin should be examined to uncover the cause of pityriasis amiantacea. This enables targeted therapy against the specific disease and prevents long term complications such as permanently bald areas.

What investigations should be done?

Skin and hair samples for mycology and bacterial culture may be useful.

Skin biopsy is rarely necessary.

Treatment

Treatment depends on the specific underlying disease.

• Mineral or vegetable oils especially olive oil may help to loosen the adherent scales.
• Washable leave-on creams or wash-off shampoos containing salicylic acid, coal tar and sulphur may be of help in reducing the scaling and inflammation, e.g. coconut compound ointment.
• Intermittent courses of topical steroids are useful for psoriasis and various types of dermatitis, often as lotions or gels.
• Antifungal shampoo (e.g. ketoconazole or ciclopirox) is often prescribed and may be helpful for underlying seborrhoeic dermatitis.
• Oral antifungal agents are necessary for confirmed tinea capitis infection.
• Oral antibiotics may be prescribed for bacterial infection.

Idiopathic pityriasis amiantacea often clears completely with treatment and does not recur. Tinea capitis may be cured by appropriate antifungal treatments. However, pityriasis amiantacea or less severe scalp scaling tends to persist or reappear when it is due to a chronic skin condition such as psoriasis or seborrhoeic dermatitis.