Multifocal discospondylitis and osteomyelitis due to Salmonella species in a cat.

Case summary: A 1-year-old male castrated Savannah cat presented with chronic recurrent lethargy, stiffness, right pelvic limb lameness and spinal hyperaesthesia. Eight months before referral, the cat was treated with prednisolone, remdesivir and a 1-week course of amoxicillin/clavulanic acid and marbofloxacin for suspected feline infectious peritonitis. Multiple recurrences were reported after initial presentation, and were treated with 1-week courses of amoxicillin/clavulanic acid. Neurological examination did not reveal further findings. Haematology showed neutrophilia/monocytosis. Spinal, limb and thoracic radiographs revealed irregular endplates and narrowing of T12-T13 and L7-S1 intervertebral disc spaces, metaphyseal lesions of multiple long bones with heterogeneous medullary bone and reduced corticomedullary distinction, and two areas of increased opacity in the left lung lobes. Feline leukaemia virus, feline immunodeficiency virus, toxoplasma serology and urine culture were negative. Blood culture was positive for Salmonella species. Amoxicillin/clavulanic acid (20 mg/kg q12h) was started with clinical improvement, but no resolution of haematological/imaging changes. Relapse occurred 7 months into treatment. Blood culture showed Phocaeicola massiliensis, a suspected contaminant. Metronidazole (11 mg/kg q12h) was added based on sensitivity, with clinical improvement but relapse after discontinuation 4 months later. Neutrophilia and monocytosis were again identified, alongside hyperproteinaemia and globulinaemia. Recheck radiographs showed a worsening of the osteomyelitis but an improvement of the discospondylitis. Salmonella species were cultured again from blood and bone biopsies. Marbofloxacin (4.5 mg/kg q24h) was initiated. At the 6-month follow-up, complete resolution of clinical and laboratory findings was documented alongside radiographic improvement of the previous lesions. Treatment was discontinued with no relapses over the 10-month follow-up.

Relevance and novel information: To our knowledge, this is the first reported case of feline discospondylitis and osteomyelitis caused by Salmonella species. Marbofloxacin, but not amoxicillin/clavulanic acid, led to resolution of the infection.