Pityriasis amiantacea

Pityriasis amiantacea is a distinct scalp disorder. It is characterized by adherent, thick, silver scales. Their asbestos-like color explains the amiantacea designation. The scales surround and bind down tufts of hair.

It is considered to be an inflammatory disease. It belongs to the spectrum of psoriasis and seborrheic dermatitis. It is probably an exaggerated inflammatory response to a primary disease of the scalp. Previous reports have suggested that pityriasis amiantacea could be a manifestation not only of psoriasis and seborrheic dermatitis, but also of lichen planus, lichen simplex chronicus, superficial fungal or pyogenic infection. In most cases fungus are not isolated from pityriasis amiantacea. In French this disorder has been called “fausse teigne amiantacée” (false tinea amiantacea).

There is a low female predilection. It is often observed in young adults, adolescents and children. Diagnosis of pityriasis amiantacea is clinical. Dermoscopy may be useful to rule out tinea capitis whose dermoscopic features include “comma” hairs, interrupted (Morse code-like) hairs, “elbow-shaped” hairs, “corkscrew” hairs, “zigzag” hairs and “question mark” hairs. But mycological cultures on conventional Sabouraud’s dextrose agar medium are necessary to definitively rule out tinea capitis. Dermoscopy demonstrates diffuse white or yellowish scaling in pityriasis amiantacea. The compact scales are thick, silver and adherent to tufts of hair.

It is generally a localized condition but widespread disease may be observed. It has been reported that pityriasis amiantacea may be associated with temporary alopecia.

Histopathology is not necessary. Scalp biopsy shows nonspecific features: diffuse hyperkeratosis and parakeratosis with follicular keratosis. A sheath of horn surround hair shaft. It has some values for distinguishing pityriasis amiantacea from other inflammatory hair disorders (psoriasis, seborrheic dermatitis, lichen simplex). A recent prospective study of 85 patients confirmed pathological diagnosis of scalp psoriasis in 35.3%, but demonstrated pathological eczematous characteristics of seborrheic and atopic dermatitis in 34.2%. In children association with seborrheic dermatitis is also reported. Some authors consider that pityriasis amiantacea is a manifestation of psoriasis. It may precede psoriasis. Cases of pityriasis amiantacea with temporary alopecia have been reported in association with paradoxical psoriasis in patient treated for Crohn’s disease with TNF alpha blockers. 

In the series of Abdel-Hamid et al. the authors detected Staphylococcus in 96.5% of the patients. In a control group of healthy patients Staphylococcus was detected in only 15%. In another series Staphylococcus aureus was also isolated in most patients with a quick improvement with topical corticosteroids in association with antibiotics. Staphylococcus aureus are probably more second colonization than primary pyogenic infection.

The treatment of pityriasis amiantacea is in most cases a topical anti-inflammatory and keratolytic treatment with topical corticosteroids and salicylic acid 5-10% ointment. Topical mineral oil is useful to remove the adherent scales. Clobetasol propionate shampoo is a powerful medication. Silver sulfadiazine cream and topical ketoconazole (2% shampoo) may be helpful. Antibiotics may be given in association in case of pyogenic infection with Staphylococcus aureus. In case of underlying disease such as psoriasis, systemic therapies may be prescribed.