Recognition of Bulbilli Facilitates the Diagnosis of Cladorrhinum bulbillosum.

PURPOSE: Necrotizing stromal keratitis caused by Cladorrhinum bulbillosum is challenging to diagnose. We report in vivo confocal microscopic and histological studies that can facilitate the diagnosis of this rare fungal infection.

METHODS

Confocal microscopy imaging and histopathological analysis of the patient's infected cornea were performed in addition to standard clinical and microbiologic methods. The diameters of chlamydoconidium (bulbilli) were measured using a calibrated micrometer.

RESULTS

C. bulbillosum was identified based on morphology observed in culture and molecular methods from a patient with a pigmented corneal infiltrate. Confocal microscopy revealed hyphal and cystic structures that have previously been mistaken for acanthamoeba. Histopathological analysis of the fungus in tissue sections showed clusters of oval structures (bulbilli) and characteristic reddish-brown septate hyphae with thin and segmented interseptal nuclei. Bulbilli measured 10 to 40 μm in diameter, whereas hyphae measured approximately 5 μm in cross section.

CONCLUSIONS

The presence of pigment in a feathery corneal infiltrate should raise the possibility of a diagnosis of Cladorrhinum sp. and prompt a search for bulbilli by confocal microscopy. In the analysis of smears or biopsies, the finding of chlamydospores greater than 10 μm in diameter associated with nuclei and pigmented hyphae should alert the pathologist that sequencing of the internal transcribed spacer sequence of ribosomal RNA may be needed to confirm the genus and species of the fungus.