Rare Fungal Infection Mimics Bone Cancer in German Shepherd Dog
First confirmed canine case of Penicillium labradoris infection in Italy highlights the importance of considering fungal disease in aggressive bone lesions.
A newly provisionally accepted case report details the first confirmed canine infection caused by Penicillium labradoris in Italy, describing a complex diagnostic journey in a German Shepherd dog whose disease initially presented like an orthopedic or neoplastic condition.
The case underscores a critical clinical reminder: not all aggressive bone lesions are cancer — some are fungal.
The Case at a Glance
In November 2021, a 10-year-old spayed female German Shepherd dog was evaluated for urinary incontinence. During the physical exam, clinicians noted a firm, non-painful soft tissue enlargement of the right forelimb. Peripheral lymph nodes were normal, and initial lab work — including CBC, chemistry panel, and urinalysis — revealed no significant abnormalities.
Despite the relatively unremarkable systemic findings, advanced imaging told a very different story.
Imaging Raises Red Flags
Radiographs revealed a proliferative lesion of the right radius
CT imaging showed aggressive proliferative and lytic changes in the radial bone, accompanied by surrounding soft tissue edema
At this stage, differentials included:
Primary bone neoplasia
Osteomyelitis
Atypical infectious disease
Cytology and Histopathology Reveal the Clue
Fine-needle aspirates from the lesion showed:
Marked neutrophilic inflammation
Moderate macrophagic inflammation
Fungal hyphae visible on cytology
A bone biopsy confirmed:
Severe fibroplasia and fibrosis
Mixed inflammatory infiltrates
Fungal elements highlighted by Grocott-Gomori methenamine silver (GMS) and PAS staining
Molecular Diagnostics Confirm a Rare Pathogen
Fungal cultures from both bone biopsy and urine samples yielded growth consistent with Penicillium species. To reach a definitive diagnosis, molecular testing was performed using sequencing of:
Internal transcribed spacer (ITS) region
β-tubulin gene
Calmodulin gene
These analyses confirmed the pathogen as Penicillium labradorum (syn. P. labradoris), making this the first documented canine case in Italy.
Treatment and Outcome
The dog was treated with itraconazole (11 mg/kg). Despite antifungal therapy, the infection progressed, and the dog died approximately 190 days after diagnosis. A necropsy was not performed due to lack of owner consent.
Disseminated fungal infections in dogs are notoriously difficult to treat and often carry a guarded to poor prognosis, especially when diagnosis is delayed.
Clinical Takeaways for Veterinarians
Aggressive bone lesions are not always neoplastic
Fungal infections should remain on the differential list, especially in large-breed dogs
Cytology and histopathology can provide early diagnostic clues
Molecular diagnostics are critical for identifying rare fungal pathogens
Disseminated fungal disease often presents with minimal early systemic abnormalities
The Bottom Line
This case highlights the value of a multidisciplinary diagnostic approach — combining imaging, cytology, histopathology, culture, and molecular testing — in uncovering rare but clinically significant infections.
For clinicians, the message is clear: when bone lesions don’t fully fit the expected pattern, think beyond cancer and include fungal disease in your diagnostic plan.
