Breed: Labrador Retriever
Spleen. Abdominal ultrasound showed numerous enlarged lymph nodes and
hypoechoic nodules in spleen. Dog in critical condition. Blood work: Moderate microcytic non-regenerative anemia, mild lymphopenia, slightly decreased albumin. Also submitted: Abdominal lymph node aspirates, pleural effusion with cultures, fever of unknown origin RealPCR panel, Coccidioides serology, and rapid growing Mycobacterium culture.
Slides are of moderate focal cellularity and consist of poorly preserved inflammatory cells in a pale blue tissue fluid background with streaming nuclear chromatin from ruptured cells and mild blood. Recognizable inflammatory cells consist of neutrophils with rare lymphocytes. Rare fungal hyphae are noted within clumps of inflammatory cells. Hyphae are pigmented, septate, and branching with parallel appearing walls. No splenic stroma, definitive lymphoid tissue, or overtly neoplastic cells are seen.
Spleen: Marked neutrophilic inflammation with fungal hyphae
Neutrophilic inflammation in the spleen suggests splenitis, necrosis, abscessation, EMH or inflammation secondary to neoplastic infiltrate. Low numbers of pigmented septate occasionally branching fungal hyphae are observed which is concerning for disseminated fungal infection. Fungal culture or PCR will be needed for definitive identification.
Abdominal lymph node aspirates revealed mixed inflammation, but no fungal organisms. The pleural effusion was classified as an exudate with no infectious agents seen and culture results were negative. The FUO RealPCR panel, Cocicioides serology, and rapid growing Mycobacterium culture were all negative.
Microscopic Interpretation of Biopsy:
Spleen: Disseminated granulomatous inflammation with abundant necrosis
GMS stain: Positive for fungal hyphae
The splenic tissue received contains evidence consistent with disseminated granulomatous inflammation, highly suspicious for fungal disease. There are rare spherical outlines, suspicious for yeasts, however, definitive identification on H&E stains is not possible.
GMS stain was applied to the tissues and revealed myriad fungal hyphae within the splenic tissue. Hyphae have parallel walls, septate, acute angle branching, and measure 2 um diameter thick. There are some forms of bulbous dilations measuring 5 um diameter. Based on morphology, a differential is Aspergillus spp.; however, fungal PCR or cultures would be required for definitive identification of this organism.
When fungal infections are caused by dimorphic fungi (Histoplasma capsulatum, Sporothrix schenkii, Blastomyces dermatitidis, Cryptococcus spp., and Coccidioides spp.) diagnosis can generally be made on cytology and/or histopathology. With filamentous fungi, morphologic characteristics including the presence or absence of septa, branching, pseudohyphal structures, and pigment help with classification; however, to obtain a definitive diagnosis, fungal culture or PCR is required.
The morphology of the fungal hyphae in this case suggest disseminated aspergillosis which is generally seen in German shepherd dogs in California, but has been reported elsewhere and with other breeds. Various species of Aspergillus have been implicated and patients become infected via inhalation with subsequent hematogenous spread. The prognosis for sick dogs is generally poor.
Day MJ. Canine disseminated aspergillosis. In: Greene CE ed. Infectious Diseases of the Dog and Cat 4th ed. St. Louis; Elsevier, 2012:662-6.