Primary acanthamoeba cutis in a patient with chronic lymphocytic leukemia on acalabrutinib. Anna Sarah Erem, Alejando A. Gru

Summary: Infections with Acanthamoeba spp. are commonly associated with granulomatous amebic encephalitis and amebic keratitis. Primary cutaneous amoebic infections are exceedingly rare, pose unique diagnostic and treatment challenges, and should be included as histological and clinical differential in immunocompromised patients. We present a case of primary Acanthamoeba cutis with no evidence of disseminated disease. A 76-year-old male with a history of chronic lymphocytic leukemia on acalabrutinib and a recent history of freshwater activities, presented with multiple nonhealing, tender, erythematous nodules with central ulcerations and black eschars on the upper extremities and thorax ranging from 1.5 to 3.5 cm. The clinical diagnoses differentials were broad: from infectious etiology, including opportunistic fungal infections, to leukemia cutis. Histology of two punch biopsies demonstrated mixed inflammatory infiltrate with histiocytic reaction and microabscesses extending throughout the epithelial layer into the deep dermis. Occasional large cells with numerous cytoplasmic vacuolations and round nuclei were highlighted on H&E. The Gomori methenamine silver (GMS) delineated double-walled cytoplasm in several large cells. The immunohistochemical stains highlighted the associated histiocytic reaction. Special stains, mucicarmine and CD45 were negative ruling out common infectious etiology, cryptococcal infection and leukemia cutis, respectively. The patient’s wound and blood cultures remained negative. The morphological and ancillary studies were most consistent with a primary cutaneous Acanthamoeba spp. infection. FLA real-time PCR was positive for Acanthamoeba species on both biopsies. The formalin-fixed, paraffin-embedded tissue blocks were sent to the Centers for Disease Control and Prevention for confirmatory diagnosis. Treatment included ketoconazole 2% topical. We would like to highlight the importance of rare etiology considerations in immunocompromised patients on new kinase inhibitors. Successful treatment outcome of Acanthamoeba cutis is multifactorial and is related to the extent of disease progression and timely diagnosis. The interdisciplinary communication and careful morphological correlates may aid in prompt recognition of this rare cutaneous etiology.