What is your diagnosis? Lymph node cytology from a dog

Severe meningoencephalitis secondary to calvarial invasion of Lagenidium giganteum forma caninum in a dog

Background:

The oomycete Lagenidiumgiganteum forma caninum is an uncommon cause of severe dermal and subcutaneous infections in dogs with possible vascular invasion and other fatal sequelae. Infection within the central nervous system of affected dogs has not been previously reported.

Case Description:

A 6-year-old spayed female mixed-breed dog was evaluated at a referral institution with a 2-month history of suspected fungal infection in the region of the right mandibular lymph node that was refractory to surgical resection and empiric medical therapy. Physical examination identified a 6-cm fluctuant subcutaneous mass caudoventral to the ramus of the right mandible and a second firm mass in the region of the right caudal maxilla. Lesional punch biopsies were submitted for fungal culture and polymerase chain reaction (PCR), which subsequently identified L. giganteum forma caninum infection. Initial treatment consisted of anti-inflammatory doses of prednisone and hyperbaric oxygen therapy. Four weeks following initial evaluation, the patient was presented with progressive neurological signs consistent with a forebrain lesion. Magnetic resonance imaging revealed soft-tissue, contrast-enhancing lesions ventral to the calvarium adjacent to the site of original surgical resection and throughout the brain. Humane euthanasia was elected, and postmortem examination was consistent with the extension of local disease from the right masseter muscle into the right ventral calvarium. Postmortem DNA sequencing confirmed the identity of the organism as L. giganteum forma caninum.

Conclusion:

This is the first reported case of intracranial lagenidiosis in the dog. PCR distinguished this species from other Lagenidium species and from oomycetes of other genera, such as Pythiuminsidiosum and Paralagenidium karlingii. Regional extension of cutaneous lagenidiosis should therefore be considered in cases with concurrent or spontaneous neurologic disease.

A biochemical screening approach to putatively differentiate mammalian pathogenic Oomycota species in the clinical laboratory

The report of four novel mammalian pathogenic species of the genus Lagenidium prompted us to study the use of biochemical assays to differentiate the Oomycota mammalian pathogens Pythium insidiosum and Lagenidium spp. We investigated the reaction of 23 Lagenidium and eight Pythium species in various biochemical assays. Because the morphological features of the Oomycota species are similar to those of species in the Entomophthoramycota and Mucormycota, five fungal species with coenocytic hyphae were also included. We found that mammalian and plant isolates of Pythium spp. all hydrolysed sucrose, but Lagenidium species and the fungal strains did not. In addition, both Pythium spp. and Lagenidium spp. were found to be maltose-positive, whereas fungal strains did not hydrolyse this sugar. The fungal species and thermo-sensitive Lagenidium giganteum and Lagenidium humanum were urease-negative, but the mammalian Lagenidium spp. and Pythium spp. hydrolysed urea within 24  h. These findings suggest these assays can be used for the presumptive differentiation of mammalian Oomycota species in the laboratory.