Laboratory Studies
In intestinal Sarcocystis infection, sporulated sporocysts in freshly voided stool can be found via a flotation technique. Sporocysts contain 4 sporozoites. Kato thick smear is a newly applied technique that is used to examine a larger fecal sample and that utilizes cellophane as a slip cover. [15] In one study, Kato thick smear was found to be highly sensitive, identifying 21 of 22 sarcocyst-infected stool samples, while direct smear identified only 1 of the 22 infected samples. [16]
CBC count usually reveals eosinophilia. [17] In cases of sarcosporidiosis with accompanying myositis, creatine kinase levels may be elevated.
Polymerase chain reaction (PCR) techniques can be used to exclude Toxoplasma gondii infection. [18]
Indirect immunofluorescent antibody test are genus-specific but not widely available.
A muscle biopsy may be useful in detecting myositis.
Toxoplasma and Sarcocystis organisms are periodic acid-Schiff (PAS)–positive; trypanosomes are PAS-negative.
Imaging Studies
Radiographs of the involved extremity may identify calcified cysts of Taenia solium (ie, cysticercosis)
CT scan or MRI of the extremities may demonstrate the cysts of sarcosporidiosis, which can grow to 5 cm in diameter.
Procedures
Excisional biopsy in the area of the painful muscle swelling can be performed for diagnostic purposes but is not needed therapeutically. [2, 17]
Histologic Findings
Intact sarcocysts observed in muscle are not associated with inflammation. The sarcocysts are septate and rather large (ie, 11 µm X 350 µm), and they can have a thick, radially striated wall. Seven distinct histopathologic types have been described. [19] The tissue form is PAS-positive. After the sarcocysts disintegrate, inflammatory cells can be observed, including lymphocytes and neutrophils and an intense eosinophilic infiltrate surrounding the muscle cyst. Localized vasculitis and fibrosis of the muscle is apparent. [20]
