Two case reports of eosinophilic fasciitis with onset after immune checkpoint inhibitor cessation.

Immune checkpoint inhibitors (ICIs) are known to cause a wide spectrum of immune-related adverse events (irAEs). Among these, eosinophilic fasciitis (EF) is a rare, fibrosing disorder causing inflammatory infiltration of subcutaneous fat and fascia. It is characterized clinically by edema and subsequent induration and tightening of the skin and subcutaneous tissues. Several case reports have documented EF secondary to ICIs in patients on active treatment. Herein, we present two cases of delayed EF following treatment cessation with avelumab for metastatic urothelial carcinoma (Case 1) and following adjuvant nivolumab completion for stage IIIC melanoma (Case 2). Both patients had typical exam findings including erythema/edema of the extremities and trunk and diffuse thickening of subcutaneous fat and fascia, leading to severe respiratory restriction in Case 1. Both patients were diagnosed with EF by full-thickness skin biopsy showing sclerosis and lymphocytic infiltration of the subcutaneous fat and/or fascia. Only one of the two patients presented with definite eosinophilia. Both cases were treated with glucocorticoids and had early recurrence of symptoms post steroid taper, necessitating subsequent protracted steroid and steroid sparing agent use. Overall, we demonstrate the importance of considering delayed irAEs, specifically autoimmune fibrotic skin diseases even when ICI therapy has been discontinued. We underscore the need for collaboration between oncology and rheumatology as the scope of ICI treatments for cancer continues to expand.