Case #369 – April 2014

A 24-year-old male with a history of granulomatous immunodeficiency had biopsy specimens taken of skin lesions on his right forearm (Figure A). Specimens were submitted to Pathology for routine histological work-up. Slides were examined by the attending pathologist and images were captured and sent to the DPDx Team for diagnostic assistance. Figures B–E show what was observed by the attending pathologist from the superficial and mid-dermis. Figure B is from a biopsy specimen stained with Gomori methenamine silver (GMS). Figures C and D are from hematoxylin-and-eosin (H&E) stained sections. Figure E is from a section stained with periodic acid-Schiff (PAS). What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

Figure E

This was a case of free-living amebic infection caused by Acanthamoeba sp. Morphologic features shown included:

the presence cysts that will stain positive for PAS (Figure E) and GMS (Figure B). As such, cysts of Acanthamoeba (and Balamuthia) but be distinguished from fungal elements.
the presence of cysts (Figures B–E) with a wrinkled outer cyst wall (exocyst) and a spherical inner cyst wall (endocyst).
the presence of trophozoites (Figure D) with large, centrally-located karyosomes and no peripheral chromatin.