Light microscopic diagnosis of microsporidiosis in patients with AIDS

In the past, the diagnosis of chronic intestinal microsporidiosis, an important cause of diarrhea in patients with AIDS, relied upon transmission electron microscopy (TEM). In this study, the sensitivity and specificity of the light microscopic (LM) diagnosis of microsporidiosis was determined.

Thirty-four consecutive jejunal biopsies from AIDS patients were evaluated at St. Luke's-Roosevelt and George Washington University Hospital Centers by several light microscopic stains, including hematoxylin and eosin, Gram stain, Giemsa stain, chromotrope 2R modified-trichrome stain, and Giemsa stain of mucosal touch preparations (TP). The results were compared to TEM, as the gold standard, and to estimates of parasite burden from plastic section light microscopy and TP.

Microsporidiosis was diagnosed by TEM in 15 cases. The diagnosis also was reached by light microscopy in most cases. The sensitivities and negative predictive values of the different techniques ranged from 57% to 88%, while the specificities and positive predictive values ranged from 94% to 100%. All stains gave concordant results in 23 of 34 cases. The parasite burden was lower by TEM (p < 0.05) and TP in cases with discordant (false-negative) results than in those with concordant results, suggesting that a false-negative diagnosis is related to a low parasite burden.

It should be possible to render the diagnosis of intestinal microsporidiosis by LM in most cases. TEM may be needed for the minority of cases with low parasite burden.