Pityriasis Amiantacea Following Bone Marrow Transplant

Clinical Findings
Clinically, lesions of PA present as matted hairs.¹ Thick scales encompass multiple hair shafts, binding down tufts of hair.^1,6,11 Patients are asymptomatic, though the lesions may be accompanied by pruritus. The hairs enclosed by the scales in some cases may be easily pulled out.⁶ Notably, alopecia often accompanies PA; it often is reversible, but in some cases, it is permanent and can lead to scarring.^9,12

Histopathology
Submission of hair specimens to histopathology usually is not performed since the diagnosis often is established based on the clinical presentation.⁵ However, submitted specimens have demonstrated spongiosis and parakeratosis along with reduction in the size of the sebaceous glands.^1,9 Additionally, follicular keratosis that surrounds the hair shafts with a sheath of horn is present.⁹ Acanthosis and migration of lymphocytes into the epidermis also have been found.¹ Often, Staphylococcus aureus isolates are detected.^9,13

Differential Diagnosis
The clinical differential diagnosis of PA includes hair casts,¹¹ pediculosis,¹⁴ and tinea capitis.¹² In PA, thick scales surround hair shafts and thus bind down tufts of hair.⁹ In patients with pediculosis, nits are attached to the hair shaft at an angle and do not entirely envelop the hair shaft.¹⁴ In addition, PA may be complicated by impetiginization; bacteria often are found in the keratin surrounding the hair shaft and represent either normal flora or secondary infection.^1,15 It has been speculated that microbial biofilms from S aureus and Staphylococcus epidermidis promote agglomeration of hair shafts and adherent scale.¹⁶ Bona fide dermatophyte infection of the scalp also may be concurrently present.¹²

Treatment
Our treatment included occlusion with mineral oil to loosen the scales from the scalp in tandem with shampoos traditionally used in patients with seborrheic dermatitis or psoriasis. Timely treatment is important to prevent scarring alopecia.^13,17 Pityriasis amiantacea may be treatment resistant, and there are no specific therapeutic guidelines; rather, therapy should be targeted at the suspected underlying condition.¹⁷ Treatment generally includes keratolytic agents, such as salicylic acid.¹⁸ These agents allow enhanced penetration of other topical agents.¹⁹ Topical antifungal shampoos such as ketoconazole and ciclopirox are recommended,¹⁸ though other topical agents, such as coal tar and zinc pyrithione, also may benefit patients.¹³ Topical corticosteroids may be used if the condition is linked with psoriasis.¹³ Systemic antibiotics are added if S aureus superinfection is suspected.⁹

A single report described successful management of a patient with severe refractory PA who was treated with the tumor necrosis factor (TNF) α inhibitor infliximab.¹³ A 47-year-old woman presented with thick adherent scale on the scalp. She was treated with coal tar for 18 months but showed no improvement; the patient was subsequently prescribed salicylic acid 10%, clobetasol solution, and coal tar shampoo. After 3 months, when no improvement was observed, the patient was offered infliximab but declined. For 6 years the patient was treated with salicylic acid 20%, clobetasol (foam, lotion, shampoo, and solution), and coal tar shampoo without improvement. She then consented to infliximab therapy; after 3 infusions at weeks 0, 2, and 6, she demonstrated notable improvement. The patient was maintained on infliximab every 8 weeks.¹³

Pathogenesis
The pathogenesis of PA has yet to be definitively established, and the condition is usually idiopathic. In addition to bacterial or fungal etiologies,^3,4 PA has been linked to medications (Table 1)^16,20,21 and systemic conditions (Table 2).^{1,3,5,7-10,12,22-25}

A PubMed search of articles indexed for MEDLINE using the search terms amiantacea, bone, drug, hair marrow, malignancy, melphalan, pityriasis, tinea, and transplant yielded 4 patients—2 men and 2 women (including our patient)—with possible drug-induced PA (Table 1)^16,20,21; however, the onset after 2 years of medication (TNF-α inhibitors) or resolution while still receiving the agent (vemurafenib) makes the drug-induced linkage weak. The patients ranged in age from 21 to 67 years, with the median age being 37.5 years. Medications included melphalan, TNF-α inhibitors (adalimumab, infliximab),^16,21 and vemurafenib²⁰; it is interesting that infliximab was the medication associated with eliciting PA in 1 patient yet was an effective therapy in another patient with treatment-resistant PA. The onset of PA occurred between 1 month (melphalan) and 24 months (TNF-α inhibitors) after drug initiation. The patients’ associated diseases included Crohn disease,^16,21 metastatic melanoma,²⁰ and multiple myeloma.

Other conditions have been described in patients with PA (Table 2). Indeed, PA may be a manifestation of an underlying inflammatory skin disease.⁹ In addition to dermatologic conditions, procedures or malignancy may be associated with the disease, as demonstrated in our patient. Most commonly, PA is seen in association with psoriasis and seborrheic dermatitis; atopic dermatitis, bacterial infection, fungal infection, lichen planus, and neurodermatitis also have been associated with PA.^{1,3,5,7-10,12,18,22-25}

Conclusion

Pityriasis amiantacea is a benign condition affecting the scalp hair. Albeit uncommon, it may appear in patients treated with medications such as melphalan, TNF-α inhibitors, and vemurafenib. In addition, it has been described in individuals with dermatologic conditions, systemic procedures, or underlying malignancy. Our patient developed PA following a bone marrow transplant after receiving conditioning with melphalan.