Background:
Pityriasis rubra pilaris (PRP) is a rare inflammatory dermatosis characterised by follicular hyperkeratosis, salmon-orange erythema, islands of sparing and palmoplantar keratoderma. Although an association between PRP and underlying malignancy has been described, its association with melanoma is rare. We present a case of PRP occurring in the setting of metastatic melanoma and breast cancer, highlighting the potential paraneoplastic association and therapeutic challenges posed.
Case:
A 79-year-old man was referred with a new superficial spreading melanoma on his back, identified during assessment of a widespread erythrodermic exfoliative eruption. The eruption had begun on the scalp and progressed cephalocaudally. Clinically, there was diffuse salmon-pink-orange erythroderma with characteristic islands of sparing involving the trunk, extremities and head, and palmoplantar keratoderma. These features were consistent with PRP. Biopsy of the rash demonstrated chronic psoriasiform dermatitis.
The melanoma was at least 1.9 mm in Breslow thickness, without ulceration or perineural invasion. It was found to be negative for a BRAF mutation. During initial clinical examination, right nipple inversion was also noted overlying a breast mass. Investigations confirmed stage IIA estrogen receptor positive breast cancer. This was treated with mastectomy and adjuvant endocrine therapy. Subsequent surveillance imaging identified left axillary nodal and dermal melanoma metastases.
Treatment for PRP included potent topical corticosteroids with methotrexate, later transitioning to acitretin 25mg daily. Given concern that immunotherapy could exacerbate his PRP, management of the stage IIIC melanoma was initially surgical only. However, due to progression to unresectable disease, treatment with immunotherapy is now indicated. With minimal improvement with acitretin, treatment of his PRP was changed to off-label risankizumab, an IL-23 inhibitor, aiming to achieve adequate control of his PRP before commencement of immunotherapy.
Discussion:
This case highlights the rare occurrence of PRP in the setting of concurrent malignancies raising the possibility of a paraneoplastic association with melanoma, although the presence of synchronous breast malignancy represents an important confounder. This case also illustrates the clinical challenge of managing significant inflammatory skin disease in a patient requiring immunotherapy.
Conclusion:
Recognition of this uncommon presentation is important, particularly when subsequent melanoma treatment with immunotherapy may impact the inflammatory dermatosis.