USA: A unique case of pityriasis amiantacea developing in a 47-year–old woman after the initiation of topical minoxidil, was reported in JAAD Case Reports.
Pityriasis amiantacea (PA) is a rare inflammatory condition of the scalp, manifested as hyperkeratotic, thick, adherent scales that bind to hair follicles and can lead to hair matting and alopecia. It predominantly affects females (60%-70%) and has a variable age of onset, however, it is commonly observed during the teenage years. Its definite etiology and pathogenesis remain unknown. It is hypothesized to be an autoinflammatory reaction pattern to a multitude of scalp diseases, including seborrheic dermatitis, psoriasis, and lichen planus. Studies have shown the role of Genetic and environmental factors in PA. In addition, there have been reports of PA development following the initiation of certain drugs, such as tumor necrosis factor α inhibitors.

Minoxidil is a stimulator of hair growth. Its mechanism of action is not completely understood, but it is thought to promote the entry of follicles into the anagen phase, indirectly increasing the time for keratinocyte proliferation while also stimulating dermal papilla and epithelial cells. This prokeratinocyte effect could play a role in the emergence of PA after treatment. In vitro studies have shown that low doses of minoxidil have proliferative effects on normal human keratinocytes, supporting this hypothesis.
The case in question is of a 47-year–old woman who was presented with a 3-month history of irritation and yellow scaling on her bitemporal scalp. Explaining the sequence of events she informed that after initiating topical minoxidil 5% foam, irritation in the form of thick, dry, yellow, asbestos-like scales circumscribing the hair shafts as well as oozing plaques was developed, which subsequently crusted. Stopping minoxidil did not affect the lesions. Also, they did not respond to any topical treatments for scalp infection.
The patient had no previous history of seborrheic dermatitis or flaking in the past and had no personal or family history of psoriasis. Clinical examination of the lesions and history led to the diagnosis of Pityriasis amiantacea. The patient was given ketoconazole 2% shampoo and clobetasol solution. The patient rapidly improved under this regimen and reported complete resolution 1 month after initiation.
This is a unique case of Pityriasis amiantacea development after the initiation of topical minoxidil and also proposes a mechanism of development. This case highlights the multifactorial pathogenesis of PA and its capacity to appear as a sequela of multiple conditions, treatments, and environmental factors. Timely diagnosis and management will help prevent serious alopecic complications of the condition.
Reference:
Wu AG, Barilla S, Madan RK. Manifestation of pityriasis amiantacea following initiation of minoxidil. JAAD Case Rep. 2022 Apr 13;24:94-96. doi: 10.1016/j.jdcr.2022.04.002.