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Case #519 – July, 2020
In Singapore, a 54-year-old man with an extensive travel history to Vietnam, Thailand, and France presented to a clinic with prolonged fever, urticarial rash, and muscle aches. Results of his blood work showed eosinophilia and elevated creatinine kinase. A muscle biopsy was performed and stained with hematoxylin and eosin (H&E) for histopathological examination. Figures A and B show what the pathologist observed at 400x and 1000x respectively. What is your diagnosis? Based on what features?
This case and images were kindly provided by Dr. Rao Pooja Rao, at Tan Tock Seng Hospital, Singapore.
Figure A
Figure B
This was a case of muscular sarcocystosis caused by Sarcocystis sp. Sarcocystosis has worldwide distribution but is more common in areas where livestock is raised. Morphologic diagnostic features of Sarcocystis sp. shown in the figures include:
- A sarcocyst embedded in skeletal muscle.
- Thick sarcocyst wall (Figure A – blue arrow).
- Many bradyzoites within the sarcocyst. The bradyzoites are the infective stage for the definitive hosts. (Figure A – black arrow; Close up Figure B – black arrow).
In contrast with intestinal sarcocystosis caused by species where humans are the definitive host (S. hominis and S. suihominis), infections of people with non-human species can result in muscle cysts with symptoms such as myalgia, muscle weakness and transitory edema, that can be accompanied by eosinophilia.
 Figure A |
 Figure B |
More on sarcocystosis
Images presented in the dpdx case studies are from specimens submitted for diagnosis or archiving. On rare occasions, clinical histories given may be partly fictitious.
DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www.cdc.gov/parasites/.