Derm Dx: Thick, sticky scales that clump to hair

Pityriasis amiantacea describes the appearance of thick, sticky, asbestos-like scales on the scalp that adheres to tufts of scalp hair. The word pityriasis means "bran-like" and is found in the names of many skin conditions that present with scale.  Pityriasis...

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Pityriasis amiantacea describes the appearance of thick, sticky, asbestos-like scales on the scalp that adheres to tufts of scalp hair. The word pityriasis means “bran-like” and is found in the names of many skin conditions that present with scale. 

Pityriasis amiantacea is not a specific disease, but rather a reaction pattern that occurs in various other scalp diseases. The most common association is psoriasis, but other causes include seborrheic dermatitis, tinea capitis and atopic dermatitis. 

In pityriasis amiantacea the thick scale forms a crust that causes groups of hairs to become matted together. Occasionally, there may be purulence beneath the crust from which Staphylococcal aureus may be cultured. Alopecia may develop in these areas. 

Pityriasis rubra pilaris is a skin condition in which small, reddish papules coalesce into large plaques that can cover a significant portion of the body-surface area. There is an associated waxy, yellow-orange, palmar-plantar keratoderma. 

In pityriasis rosea, patients present with mildly scaly, round-to-oval patches located mainly on the trunk and proximal extremities that form a characteristic “Christmas tree” pattern. A single, larger “herald patch” frequently precedes the generalized eruption. The etiology of pityriasis rosea is unknown, but many authors believe it is a viral exanthem.

Pityriasis lichenoides is a spectrum of diseases. The acute variant is called pityriasis lichenoides et varioliformis acuta (PLEVA). PLEVA occurs with the sudden eruption of reddish macules, papules and papulovesicles that become crusted and may form small scars.

In the chronic form, pityriasis lichenoides chronica (PLC), patients develop subtle, scaly erythematous macules and papules that resolve with hypopigmentation.

Diagnosis & Treatment

Pityriasis amiantacea diagnosis is based on the clinical appearance of sticky scalp scale clumped onto clusters of hairs. Because the cause is most commonly psoriasis or seborrheic dermatitis, clinicians should look for other signs of these diseases. If tinea capitis is suspected, a potassium hydroxide preparation or a fungal culture may be performed. 

Pityriasis amiantacea treatment consists of daily shampooing with selenium sulfide, tar or steroid shampoo. Applying peanut oil or olive oil, which can be compounded with topical corticosteroids or salicylic acid, helps soften the scale and crust and allows for easier removal when shampooing. After shampooing steroid containing solution or oil should be applied.

In cases caused by psoriasis, systemic therapy may be required if topical measures fail. Similarly, cases involving tinea capitis should be treated with a course of oral antifungals, such as terbinafine. 

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.