Case: AP313
Contributor's Comment: The lymph node shows the typical morphologic features of Toxoplasmic lymphadenitis. However, the features, while highly characteristic, are not entirely specific, and thus the final etiologic diagnosis rests on serologic findings.

Two participants suggest the use of immunohistochemistry for Toxoplasma gondii to support the diagnosis. This is neither necessary nor indicated. Toxoplasmic lymphadenitis is basically a lymph node reaction to Toxoplasma infection, and does not represent direct infection of the lymph node by Toxoplasma gondii. Therefore Toxoplasma organisms are almost never found.

Some participants also suggest using PCR for Toxoplasma gondii on the lymph node to support the diagnosis. This is still a very controversial issue. One study from Stanford has shown this to have a very low sensitivity (only 1 of 9 cases positive). Other studies from Taiwan and China, using semi-nested PCR, have reported higher sensitivity (such as 83% in one Taiwan study), but then other lymph node conditions (including lymphoma) can also show positivity (27%). Therefore currently such PCR test lacks specificity.(JKCC)