PMC9845947_01
Clinical manifestations and histopathological features. (A) Erythematous patches and tense bullae on the patient's trunk and extremities (CTCAE grade 3). (B) Numerous large tense bullae on the hand. (C) Histopathologic examination of a skin lesion on the right hand revealed a subepidermal blister cavity (H&E, 100x). (D) Eosinophils infiltrated the upper and mid-dermis (400x). Immunostaining revealed (E) a predominantly CD4+ (400x) lymphocytic infiltrate, with (F) a few CD8+ cells (400x) and the occasional CD20+ cell.
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Multiple vesicles and tense bullae, some with adjacent erosions and crusting, developed on his trunk and extremities following discontinuation (~22 days) of pembrolizumab ( Figures 1A, B ). A biopsy examination of the bulla revealed a subepidermal blister cavity with associated dermal lymphocytic and eosinophil infiltration ( Figures 1C, D ). In addition, immunohistochemical studies of tissue sections predominantly showed CD4+ cells, a few CD8+ cells, and the occasional CD20+ lymphocytic infiltrate ( Figures 1E, F ).
(A, C) A baseline computed tomography scan taken before treatment with ICI therapy, demonstrating the left lung mass. (B, D) A computed tomography scan taken at the time of BP development (6 weeks after pembrolizumab discontinuation), showing a partial response.
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At 5 weeks of follow-up, the left lung mass showed partial response (PR) and became an irregularly cave on a computed tomographic scan ( Figure 2 ).
The eosinophil count (reference range, 0.02-0.05x109/L) in the peripheral blood was concomitantly increased with the activity of the vesicles but plummeted after IVIG administration.
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Eosinophil count in the peripheral blood was concomitantly increased with the activity of the vesicles ( Figure 3 ).
Case timeline. PR, partial response.
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The case timeline is shown in  Figure 4 .