• View in gallery
    Figure 1

    Lateral (A) and craniocaudal (B) radiographic projections of the left femur of a 4.5-month-old 2.5-kg sexually intact male domestic shorthair cat with a 2-week history of weight-bearing lameness of the left hind limb.

  • View in gallery
    Figure 2

    Same images as in Figure 1. A focal expansile lesion with permeative lysis (arrowheads) is in the distal metaphysis of the left femur. A smooth, thickened, and circumferential periosteal reaction (arrows) is visible. In addition, there is evidence of cortical destruction and a wide transition zone between the lesion and the normal bone. The distal physis of the femur appears radiographically normal.

  • View in gallery
    Figure 3

    Sequential follow-up lateral (A) and craniocaudal (B and C) radiographic images of the left femur on day 45 (A and B) and day 149 (C) after the first visit (40 and 144 days after onset of treatment, respectively). On day 45 (A and B), the bone lesion remains expansile and extends more proximally with complete cortical destruction at the distal half of the femur. A less evident permeative lysis is observed, but some linear trabecular patterns are visible instead (arrowheads). The periosteal new bone is remodeled and becomes thinner (arrows). On day 149 (C), the lesion is less expansive and has remodeled to form a cortex and medulla.

  • 1.

    Gieling F, Peters S, Erichsen C, Richards RG, Zeiter S, Moriarty TF. Bacterial osteomyelitis in veterinary orthopaedics: pathophysiology, clinical presentation and advances in treatment across multiple species. Vet J. 2019;250:4454.

    • Search Google Scholar
    • Export Citation
  • 2.

    Dunn JK, Dennis R, Houlton JEF. Successful treatment of two cases of metaphyseal osteomyelitis in the dog. J Small Anim Pract. 1992;33:8589.

    • Search Google Scholar
    • Export Citation
  • 3.

    Sainato D, Cinti F, Renfrew H. Sterile osteomyelitis in the ulnar diaphysis of a young indoor cat. JFMS Open Rep. 2020;6:2055116919899754.

    • Search Google Scholar
    • Export Citation
  • 4.

    Helm J, Morris J. Musculoskeletal neoplasia: an important differential for lumps or lameness in the cat. J Feline Med Surg. 2012;14:4354.

    • Search Google Scholar
    • Export Citation
  • 5.

    Viskjer S, Rapp M. Scapular osteomyelitis in an immature domestic shorthair cat. JFMA Open Rep. 2016;2:2055116916668199.

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Ting-Yi ChenVeterinary Medical Teaching Hospital, College of Veterinary Medicine, National Chung Hsing University, Taichung, Taiwan

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Jian-Liang LinLittle Prince Animal Hospital, Taipei, Taiwan

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Kuan-Sheng ChenVeterinary Medical Teaching Hospital, College of Veterinary Medicine, National Chung Hsing University, Taichung, Taiwan
Department of Veterinary Medicine, College of Veterinary Medicine, National Chung Hsing University, Taichung, Taiwan

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Abstract

In collaboration with the American College of Veterinary Radiology

Abstract

In collaboration with the American College of Veterinary Radiology

History

A 4.5-month-old 2.5-kg sexually intact male domestic shorthair cat was presented because of a 2-week history of mild weight-bearing lameness of the left hind limb. On physical examination, swelling of the left distal femur was palpated; the swollen region was firm, and no sign of pain was induced. The cat was bright, alert, and responsive and had a rectal temperature within reference limits. No other abnormalities were observed in the cat. The Hct and serum biochemical results were unremarkable. Radiographic images of the left femur were obtained (Figure 1).

Figure 1
Figure 1
Figure 1

Lateral (A) and craniocaudal (B) radiographic projections of the left femur of a 4.5-month-old 2.5-kg sexually intact male domestic shorthair cat with a 2-week history of weight-bearing lameness of the left hind limb.

Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.21.05.0251

Formulate differential diagnoses, then continue reading.

Diagnostic Imaging Findings and Interpretation

Radiography revealed a focal expansile lesion centered in the distal metaphysis of the left femur, extending to the distal diaphysis, with a smooth brush-border periosteal reaction and a wide transition zone (Figure 2). The distal third cortex was completely destroyed, and multiple regions of permeative lysis were evident. The distal physis appeared radiographically normal. The radiographic findings were compatible with a monostotic aggressive bone lesion at the distal metaphysis of the left femur. The most likely differential diagnoses for this bone lesion included osteomyelitis (eg, bacterial or fungal) and, less likely because of the young age of the cat, primary or metastatic bone tumors.

Figure 2
Figure 2
Figure 2

Same images as in Figure 1. A focal expansile lesion with permeative lysis (arrowheads) is in the distal metaphysis of the left femur. A smooth, thickened, and circumferential periosteal reaction (arrows) is visible. In addition, there is evidence of cortical destruction and a wide transition zone between the lesion and the normal bone. The distal physis of the femur appears radiographically normal.

Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.21.05.0251

Treatment and Outcome

Cage rest was advised, but the swollen femur was more pronounced 5 days later on the second visit, and a subsequent surgical core biopsy of the distal metaphysis of the left femur was performed for histopathologic and microbiological analyses. While awaiting laboratory results, amoxicillin-clavulanate (13.75 mg/kg, PO, q 12 h for 7 days), itraconazole (5 mg/kg, PO, q 24 h for 7 days), and meloxicam (0.05 mg/kg, PO, q 24 h for 3 days) were prescribed. Histopathologic examination revealed no neoplastic lesions in any of the submitted specimens, and histochemical staining revealed small numbers of gram-positive short rod-shaped bacteria in some foamy macrophages, but the aerobic and anaerobic microbiological and fungal cultures yielded no growth. A diagnosis of suppurative to pyogranulomatous osteomyelitis was made histopathologically, and the same antimicrobial medication with amoxicillin-clavulanate and itraconazole was continued for 8 weeks. Sequential follow-up radiography of the left femur was performed on days 45 and 149 from the first visit (Figure 3). On day 45, the lesion extended more proximally with complete cortical destruction at the distal half of the femur; there was less permeative lysis, and some linear trabecular patterns were observed. The periosteal new bone became thinner, and the cat showed no sign of lameness or pain. On day 149, the expansile lesions were radiographically smaller; although the distal half of the cortex was completely destroyed, bone remodeling had formed a new cortex and medulla.

Figure 3
Figure 3
Figure 3
Figure 3

Sequential follow-up lateral (A) and craniocaudal (B and C) radiographic images of the left femur on day 45 (A and B) and day 149 (C) after the first visit (40 and 144 days after onset of treatment, respectively). On day 45 (A and B), the bone lesion remains expansile and extends more proximally with complete cortical destruction at the distal half of the femur. A less evident permeative lysis is observed, but some linear trabecular patterns are visible instead (arrowheads). The periosteal new bone is remodeled and becomes thinner (arrows). On day 149 (C), the lesion is less expansive and has remodeled to form a cortex and medulla.

Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.21.05.0251

Comments

Osteomyelitis is uncommon in cats and is clinically characterized by lameness, swelling, heat, pain, draining tracts, and localized erythema.1 The disease is often caused by infection with pyogenic organisms. It can develop from direct inoculation by penetrating wounds, postsurgical repair, or hematogenous dissemination.1 The latter condition is less common and typically affects juveniles. Hematogenous osteomyelitis often occurs in the metaphysis and epiphysis of multiple long bones due to the formation of vascular anastomoses that leads to a sluggish blood flow and predisposes to the seeding of bacteria.1,2 For the cat of the present report, infection from a previous small trauma wound was more likely than from the hematogenous route because of the monastic lesion and lack of systemic illness.

Radiographic features of osteomyelitis include soft tissue swelling, periosteal new bone proliferation, cortical bone destruction, or bone sequestration.1 Findings for the cat of the present report demonstrated not only periosteal proliferation and cortical bone destruction but also an expansile appearance, which has not been commonly described. From a literature review, similar imaging characteristics have been described in 2 young cats diagnosed with osteomyelitis.3,4 Each demonstrated monostotic aggressive expansile bone lesions at the scapula and ulnar diaphysis with osteomyelitis and sterile osteomyelitis, respectively.3,4

Osteosarcoma is another differential diagnosis, which is the most common skeletal neoplasia in cats.5 It has been reported in young cats (less than 1 year of age), although it is rare.5 The radiographic changes of osteosarcoma range from purely lytic to proliferative and often involve the metaphysis of the appendicular skeleton.5 Osteomyelitis cannot be distinguished from osteosarcoma based on radiographic findings alone. Therefore, bone lesion biopsy for histopathologic and microbiological examination is needed to obtain a definite diagnosis.

The most commonly isolated organisms from bacterial osteomyelitis are staphylococcal and streptococcal species.1 For the cat of the present report, antimicrobial treatment was commenced based on the histopathologic examinations despite the negative results for microbiological culture. There are reports of lack of growth in culture, but animals have responded well to antimicrobial treatment.3,4 The explanations for no growth on culture include sterile osteomyelitis,4 specimen handling, or limited culture conditions.1,3 Because gram-positive short rod-shaped bacteria were histopathologically identified in some macrophages, sterile osteomyelitis was unlikely. No antimicrobials were prescribed until bone biopsy was performed in this case, and the cat responded well after antimicrobial treatment; negative results of microbiological culture may be associated with specimen handling or culture technique.

Acknowledgments

The authors received no extrainstitutional funding associated with the present report, and the authors declare that there were no conflicts of interest.

References

  • 1.

    Gieling F, Peters S, Erichsen C, Richards RG, Zeiter S, Moriarty TF. Bacterial osteomyelitis in veterinary orthopaedics: pathophysiology, clinical presentation and advances in treatment across multiple species. Vet J. 2019;250:4454.

    • Search Google Scholar
    • Export Citation
  • 2.

    Dunn JK, Dennis R, Houlton JEF. Successful treatment of two cases of metaphyseal osteomyelitis in the dog. J Small Anim Pract. 1992;33:8589.

    • Search Google Scholar
    • Export Citation
  • 3.

    Sainato D, Cinti F, Renfrew H. Sterile osteomyelitis in the ulnar diaphysis of a young indoor cat. JFMS Open Rep. 2020;6:2055116919899754.

    • Search Google Scholar
    • Export Citation
  • 4.

    Helm J, Morris J. Musculoskeletal neoplasia: an important differential for lumps or lameness in the cat. J Feline Med Surg. 2012;14:4354.

    • Search Google Scholar
    • Export Citation
  • 5.

    Viskjer S, Rapp M. Scapular osteomyelitis in an immature domestic shorthair cat. JFMA Open Rep. 2016;2:2055116916668199.

Contributor Notes

Corresponding author: Dr. Chen (kschen@dragon.nchu.edu.tw)