Value of lymph node biopsy in the diagnosis of acquired toxoplasmosis.

Toxoplasmic lymphadenitis generally involves a solitary lymph node in the head and neck regions, without systemic symptoms. In order to determine the frequency of toxoplasmic lymphadenitis, we reviewed the histological sections of 731 consecutive patients with reactive lymph node hyperplasia. Amongst 731 patients, 112 had histological features supporting a diagnosis of toxoplasmic lymphadenitis (15.3 per cent). In 80 of these patients (71 per cent), either Indirect Haemaglutination test (IHA), in 37 cases, or the Enzyme-Linked Immunosorbent Assay (ELISA) for detecting toxoplasmic IgG or IgM antibodies, in 43 cases, were performed. In 76 out of 80 patients (95 per cent), histological features correlated well with serological studies. The IHA test was positive in 30 patients with a titre of 1/64 or higher. The IgG-ELISA test was positive in 11 whereas the IgM-ELISA test was positive in 28 patients. These results provide further evidence of the distinctive nature of the histological changes in toxoplasmic lymphadenitis, which should enable the clinician to make a confident diagnosis of acute acquired toxoplasmosis.