Abstract

Acanthamoeba is a free-living ameba, present ubiquitously in soil and water, known to most commonly cause granulomatous amebic encephalitis and amebic keratitis in immunocompromised patients. Cutaneous acanthamebiasis is a rare single-organ manifestation of acanthamoeba infection with only 16 cases recorded in the United States between 1956 - 2020. 

Here we present two cases of cutaneous acanthamebiasis. Case one is an 81 year old patient with a history of diffuse large B-cell lymphoma on Idelalisib presenting with widespread nodules on his extremities that developed and ulcerated over the course of 3 weeks. A nodule on the left arm exhibited a mixed deep dermal infiltrate with abundant neutrophils and histiocytes while a nodule on the right arm contained a granulomatous pattern with lymphoplasmacytic inflammation. Case two is a 23 year old hospitalized patient with systemic lupus erythematosus and pancytopenia who acutely developed erythematous indurated nodules on her extremities. A right thigh nodule biopsy showed extensive inflammation by a lymphohistiocytic infiltrate with admixed neutrophils and associated fat necrosis.  

Although all specimens demonstrated distinct inflammatory reactions, amebic trophozoites and cysts were identified in each specimen, highlighted by PAS special stain. Both cases were subsequently confirmed as Acanthamoeba species by polymerase chain reaction (PCR).

Cutaneous acanthamebiasis should be included in the differential diagnosis of cutaneous nodules in immunocompromised patients. Clinical presentation may vary and the histopathology of biopsies taken from these nodules may have differing inflammatory reactions; awareness of the clinical and pathological features of free-living amebas is essential for timely diagnosis.