6. Treatment resistant ulcerating dermatomyositis in metastatic melanoma treated with checkpoint inhibitor therapy

INTRODUCTION: Paraneoplastic dermatomyositis is a well-recognised clinical entity, and should prompt investigation for an underlying malignancy. Immunosuppressive treatment can be effective in control of both skin and muscle disease. The effect of checkpoint inhibitors for control of solid tumours on autoimmune paraneoplastic phenomena is yet to be fully understood. CASE DESCRIPTION: A 49-year-old female with a background of melanoma on the left thigh 2014 (Breslow thickness 1.9mm, treated with wide local excision only) presented with classical features of dermatomyositis; facial erythema, V-sign, Gottron’s papules, muscle weakness and elevated creatine kinase (CK) at 711 IU/L. An MRI of the upper arms was consistent with myositis. Myositis ENA panel was negative. She was initially treated with high dose oral prednisolone and weekly methotrexate. At presentation, there was no clinical or radiographic evidence of recurrent melanoma, but unfortunately after 7 months she developed a lump in the left groin which proved to be metastatic melanoma (stage IV M1a). She was treated with 3 months palliative pembrolizumab, but this was discontinued due to lack of clinical response, when an interval CT scan showed increasing volume of disease (progressive left pelvic, retroperitoneal and left supra-clavicular fossa lymphadenopathy). Her skin disease remained painful despite 20mg PO prednisolone and 25mg of subcutaneous methotrexate weekly, so she was treated with intravenous immunoglobulin (IVIG) 2g/kg planned to be given over 5 days. On day 3, she was found to be pyrexial at 38.2 degrees celcius prior to commencement of the infusion. Treatment was delayed by 2 days. On day 6 she was again apyrexial and the IVIG treatment was completed with IV paracetamol and 100mg IV hydrocortisone given alongside. Following the IVIG, she has developed areas of painful localised ulceration over the dorsi of her feet, limbs and forehead. Her skin disease remains active with facial swelling and erythema, florid Gottron’s papules and periungual erythema. The ulcerated areas are discrete from the areas of known metastasis, and are considered to be secondary to severe dermal inflammation which is being treated with betnovate ointment, with a plan to introduce hydroxychloroquine if there is no clinical improvement. DISCUSSION: The use of checkpoint inhibitors to treat solid tumours is increasing. The autoimmune side effects of this group are well documented, and pembrolizumab is known to trigger dermatitis as a treatment related adverse event. However, the implications for checkpoint inhibitor use in an existing paraneoplastic autoimmune phenomenon is not yet understood. KEY LEARNING POINTS: Thorough investigation for underlying malignancy is paramount in new dermatomyositis. Patients treated with checkpoint inhibitors should be monitored closely for disease activity. CONFLICTS OF INTEREST: The authors have declared no conflicts of interest.