Infectious Agents
Case 3

Clinical Features
Light Microsocopy
Electron Microscopy
Discussion

Case 1
Case 2
Case 3
Case 4

Electron Microscopy of Infectious Agents

Case 3: Toxoplama Encephalitis

Discussion

There is no question that this patient had a worsening clinical course that required accurate and rapid diagnostic intervention, and that electron microscopy provided the crucial clue that focused subsequent tests toward the appropriate diagnosis. The EM findings of a protozoan in the affected tissue early in the diagnostic process allowed selection of an effective therapy in a timely fashion. The EM findings became more important because all cultures from the brain tissue were negative, the post transplant CSF contained no detectable toxoplasma-specific antibodies, and studies by immunofluorescent microscopy of paraffin sections of brain tissue were non-diagnostic. Only the immunoperoxidase stains for T. gondii performed weeks later were positive for the organism.

Direct electron microscopic visualization of characteristic structures in this case allowed for distinction between other members of the Coccicia Order, and conclusively identified the infecting organism as Toxoplasma gondii based on the presence of more than 4 rhoptries in the cells. The other Coccidia possess only 1 or 2 pairs of rhoptries (2).

The expedited processing schedule for EM provided sections for study within five hours of biopsy, with excellent preservation of morphological details so that the important ultrastructural features were clearly recognizable. Rapid processing schedules (3) should be available in every diagnostic electron microscopy laboratory in addition to the standard schedules so that results can be rendered when there is a clinical need for expedited processing.

References

1. Cerezo, L., Alvarez, M., and Price, G.: Electron microscopic diagnosis of cerebral toxoplasmosis. J. Neurosurg 63:470-472, 1985.
2. Tang, T.T., Harb, J.M., Dunne, W. M., et al.: Cerebral toxoplasmosis in an immunocompromised host. Am. J. Clin. Pathol. 85:104-110, 1986.
3. Harb, J.M.: Preparation of diagnostic specimens for transmission electron microscopy. Proceedings of the 42nd meeting of the Electron Microscopy Society of America. Ed. G.W. Bailey, San Francisco, San Francisco Press, pp 62-65, 1984.

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Case 2

Case 3

Case 4