Despoina Douralidou, Laura Muñiz-Moris, Miguel Solano, Lorenzo Mari

Background

Discospondylitis and osteomyelitis are inflammatory infections of the intervertebral discs, vertebral endplates, and bone, typically resulting from hematogenous spread. While these conditions are uncommon in cats, previously identified pathogens include Escherichia coli, Staphylococcus spp., Mycobacterium spp., Streptococcus spp., Microsporum canis, and Bartonella henselae. Salmonella infection has been reported in feline systemic and urinary disease but not in spinal or skeletal infections. This case documents what appears to be the first feline instance of multifocal discospondylitis and osteomyelitis caused by Salmonella species.

Methods

A 1-year-old Savannah cat with chronic lethargy, lameness, and spinal hyperaesthesia underwent neurological and orthopedic examinations, hematology, biochemistry, infectious disease testing, radiography, ultrasound, and serial blood cultures. Diagnostic imaging identified discospondylitis and multifocal osteomyelitis. Blood cultures were performed at multiple timepoints to identify causative organisms. Later in the disease course, bone biopsies were obtained for histopathology and culture. Antibiotic treatments were adjusted based on sensitivity testing and clinical response. Serial radiographs and hematologic monitoring were used to assess treatment efficacy.

Results

Initial blood culture identified Salmonella species sensitive to amoxicillin/clavulanate, and prolonged treatment led to clinical but not radiographic improvement. After relapse, a second culture grew Phocaeicola massiliensis, suspected to be a contaminant. Despite adding metronidazole, neutrophilia and radiographic evidence of osteomyelitis persisted. Following recurrence after discontinuing antibiotics, radiographs showed progression of osteomyelitis while discospondylitis partially improved. Repeat blood and bone cultures again isolated Salmonella species. Initiation of marbofloxacin resulted in complete clinical, hematological, and radiographic resolution within six months, with no relapse at ten-month follow-up.

Limitations

As a single case report, conclusions on antibiotic selection and treatment duration cannot be generalized. The study lacked advanced imaging such as MRI for monitoring. Biomarkers such as alpha-1-acid glycoprotein and globulins fluctuated and did not reliably track disease progression, and serum amyloid A was not measured. The potential emergence of in vivo resistance to amoxicillin/clavulanate could not be confirmed, as no change in sensitivity profile was documented.

Conclusions

This case represents the first documented feline discospondylitis and osteomyelitis due to Salmonella species. Despite in-vitro sensitivity to both amoxicillin/clavulanate and marbofloxacin, only marbofloxacin achieved full clinical, hematologic, and radiographic resolution. The report highlights the need for regular radiographic and hematological monitoring rather than relying solely on clinical improvement. Further research is required to determine optimal antibiotic regimens, duration, imaging follow-up schedules, and appropriate biomarkers for managing these conditions in cats.

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