Photographs of the left hind limb of a 14-week-old sexually intact female Boxer referred for evaluation of non–weight-bearing lameness of the left forelimb that became noticeable 5 days after vaccination against canine distemper virus, canine infectious hepatitis, leptospirosis, canine parainfluenza virus, and canine parvovirus. During a 3-day period after initial evaluation, progressive swelling of both hind limbs rendered the dog laterally recumbent and vocalizing. The dog was euthanized. A—Notice that the subcutaneous tissue is expanded by inflammatory exudates, including marked edema. B—Pockets of opaque tan-red fluid dissect between muscles and separate periosteum from the femur. The muscles have variable degrees of pallor and red to tan mottling. The subperiosteal surface of the femoral diaphysis is diffusely roughened.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Photographs of the left hind limb of a 14-week-old sexually intact female Boxer referred for evaluation of non–weight-bearing lameness of the left forelimb that became noticeable 5 days after vaccination against canine distemper virus, canine infectious hepatitis, leptospirosis, canine parainfluenza virus, and canine parvovirus. During a 3-day period after initial evaluation, progressive swelling of both hind limbs rendered the dog laterally recumbent and vocalizing. The dog was euthanized. A—Notice that the subcutaneous tissue is expanded by inflammatory exudates, including marked edema. B—Pockets of opaque tan-red fluid dissect between muscles and separate periosteum from the femur. The muscles have variable degrees of pallor and red to tan mottling. The subperiosteal surface of the femoral diaphysis is diffusely roughened.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Photographs of the left hind limb of a 14-week-old sexually intact female Boxer referred for evaluation of non–weight-bearing lameness of the left forelimb that became noticeable 5 days after vaccination against canine distemper virus, canine infectious hepatitis, leptospirosis, canine parainfluenza virus, and canine parvovirus. During a 3-day period after initial evaluation, progressive swelling of both hind limbs rendered the dog laterally recumbent and vocalizing. The dog was euthanized. A—Notice that the subcutaneous tissue is expanded by inflammatory exudates, including marked edema. B—Pockets of opaque tan-red fluid dissect between muscles and separate periosteum from the femur. The muscles have variable degrees of pallor and red to tan mottling. The subperiosteal surface of the femoral diaphysis is diffusely roughened.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
History
A 14-week-old sexually intact female Boxer was referred for evaluation of non–weight-bearing lameness of the left forelimb 5 days after vaccination against canine distemper virus, canine infectious hepatitis, leptospirosis, canine parainfluenza virus, and canine parvovirus.
Clinical and Gross Findings
A suspected fractured left humeral condyle was observed on radiographic views. The limb was placed in a sling, and carprofen was prescribed. Two days later, the dog was unable to use either hind limb. The left hind limb was swollen at the thigh region, and the right hind limb had a firm swelling over the lateral aspect of the tarsus. The swollen areas were painful on palpation. Butorphanol, prednisone, and IV fluid therapy were administered. Three days after the initial evaluation, the dog was laterally recumbent and vocalizing, and the right hind limb swelling had worsened. The owners elected euthanasia, and the dog was submitted for necropsy.
Subcutaneous tissue of all limbs and along the dorsal midline was variably expanded by edema. Opaque tan-red to translucent straw-colored fluid tracked along fascial planes, separating muscles of all limbs and the trunk. Muscles were easily separated from each other and from the adjacent bone. Affected muscle tissue contained multiple, variably sized irregular foci that were mottled tan-yellow with red rims and were interspersed with regions of varying pallor (Figure 1).
Along the entire left femoral diaphysis, multiple pockets of opaque tan-red fluid separated the periosteum from the bone and extended into the left hip joint. The cortical surface of the left femur was diffusely tan and rough. The greater trochanter snapped off at the physis with minimal digital pressure. The medial aspect of the proximal metaphysis and the articular cartilage over the medial aspect of the condyle of the left humerus were rough, pitted, and mottled tan to red. The proximal physis of the right humerus was soft and mottled tan to dark red. Thick yellow exudate filled the left elbow joint. The right talocrural joint was filled with tan-red opaque fluid.
Additional gross findings included an epidermal pustule (0.6 × 1 cm) located to the right of the vulva; two 2- to 3-mm abscesses in the parietal pleura; lymphadenomegaly of the popliteal, axillary, superficial cervical, and sternal lymph nodes; pulmonary congestion and edema; mild hydropericardium; and mild hydroperitoneum. Samples of the left hind limb skeletal muscle, lung, liver, and spleen tissues and swab samples from the left elbow joint and peritoneum were submitted for bacterial culture and identification.
Photomicrograph of a section of skeletal muscle obtained from the left hind limb of the dog in Figure 1. The perimysium and epimysium are expanded by edema with fibrin and low numbers of leukocytes. H&E stain; bar = 250 μm.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Photomicrograph of a section of skeletal muscle obtained from the left hind limb of the dog in Figure 1. The perimysium and epimysium are expanded by edema with fibrin and low numbers of leukocytes. H&E stain; bar = 250 μm.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Photomicrograph of a section of skeletal muscle obtained from the left hind limb of the dog in Figure 1. The perimysium and epimysium are expanded by edema with fibrin and low numbers of leukocytes. H&E stain; bar = 250 μm.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Photomicrograph of a section of skeletal muscle obtained from the left hind limb of the dog in Figure 1. In this section, the perimysium and epimysium are expanded by edema, hemorrhage, fibrin, and necrotic cellular debris, admixed with macrophages, neutrophils, and colonies of cocci (star). Some muscle cells are necrotic and infiltrated by macrophages and neutrophils (arrow). H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Photomicrograph of a section of skeletal muscle obtained from the left hind limb of the dog in Figure 1. In this section, the perimysium and epimysium are expanded by edema, hemorrhage, fibrin, and necrotic cellular debris, admixed with macrophages, neutrophils, and colonies of cocci (star). Some muscle cells are necrotic and infiltrated by macrophages and neutrophils (arrow). H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Photomicrograph of a section of skeletal muscle obtained from the left hind limb of the dog in Figure 1. In this section, the perimysium and epimysium are expanded by edema, hemorrhage, fibrin, and necrotic cellular debris, admixed with macrophages, neutrophils, and colonies of cocci (star). Some muscle cells are necrotic and infiltrated by macrophages and neutrophils (arrow). H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1389
Histopathologic and Microbiological Findings
Sections of skeletal muscle, skin, right humerus, and left femur were examined microscopically (Figures 2 and 3). In sections of skeletal muscle and skin, perimysium and epimysium were variably expanded by edema, hemorrhage, fibrin, and necrotic cellular debris, admixed with randomly scattered neutrophils, macrophages, and colonies of cocci in chains. The inflammatory exudate extended into adjacent subcutaneous tissue and in some sections into the deep dermis. Some blood vessels had mural fibrinoid necrosis and were occluded by fibrin thrombi with or without bacterial colonies. Blood vessels in affected regions were variably surrounded by neutrophils, macrophages, and fewer lymphocytes. The myocytes adjacent to the inflammatory exudates were multifocally necrotic.
The medullary cavities of the right humerus and left femur contained variable amounts of necrotic debris, hemorrhage, fibrin, and large numbers of colonies of cocci. The adjacent cortical bone, trabecular bone, and physeal cartilage had necrosis or loss of osteocytes and chondrocytes. The periosteum of the right humerus was focally separated from the proximal metaphysis by a mixture of hemorrhage, immature collagen, fibroblasts, neutrophils, macrophages, and colonies of cocci. Such inflammatory exudates along with osteoclasts breached the cortical bone and infiltrated the adjacent medullary space.
Bacterial culture of samples of left hind limb skeletal muscle, lungs, liver, and spleen tissues yielded pure growths of Streptococcus canis. Similarly, S canis was isolated from the swab samples obtained from the left elbow joint and peritoneum.
Morphologic Diagnosis and Case Summary
Morphologic diagnosis: acute, regionally extensive necrotizing fasciitis, with myonecrosis, cellulitis, and intralesional cocci in the skeletal muscle and skin and acute, regionally extensive necrotizing osteomyelitis with intralesional cocci of the right humerus and left femur.
Case summary: necrotizing fasciitis, osteomyelitis, and streptococcal septicemia in a dog.
Comments
For the dog of the present report, the gross, histopathologic, and microbiological findings supported a diagnosis of necrotizing fasciitis, osteomyelitis, and streptococcal septicemia. Necrotizing fasciitis in dogs is most commonly caused by β-hemolytic Lancefield group G streptococci, typically S canis.1,2 Streptococcus canis is a commensal organism of dogs and is capable of causing opportunistic infections.2,3 Streptococcus canis produces exotoxins and proteolytic enzymes that facilitate spread along fascial planes and invasion of subcutaneous tissue by the organism.2,4 Some dogs with streptococcal necrotizing fasciitis develop streptococcal toxic shock syndrome, which is characterized by hypotension, multiorgan failure, and the isolation of streptococci from normally sterile sites.2 Although S canis is the most common cause of necrotizing fasciitis in dogs, Staphylococcus pseudintermedius and Escherichia coli have been reported to cause similar lesions.5,6
Necrotizing fasciitis is a rapidly progressing and potentially fatal bacterial infection of subcutaneous tissue and fascial planes.1,7 A patient's history can be nonspecific and may include reports of injury a few days before the appearance of clinical signs.1,3,4,7,8 In the case described in the present report, cutaneous wounds were not observed at necropsy. The dog had been vaccinated 5 days prior to the onset of lameness; however, whether the injection site was the source of infection cannot be determined. Dogs with necrotizing fasciitis are often lethargic with fever and localized soft tissue inflammation.1,2,7 One of the hallmark signs is evidence of extreme pain disproportionate to the gross appearance of the affected region.2,4,8 Most cases involve the limb, but the neck and ventral aspect of the thorax can also be affected.1,2,4
Necrotizing fasciitis causes extensive necrosis of fascia, subcutis, and vasculature.7 Infection spreads rapidly and tracks along fascia and subcutaneous tissue.4,8 Spread of infection beneath the skin can be difficult to detect during physical examination because the epidermis may appear grossly normal despite deep tissue necrosis.7,8 Occlusion of blood vessels by thrombosis can lead to necrosis of overlying skin and underlying muscle.4,7,8 Humans with necrotizing fasciitis may develop cutaneous bullae, but these develop infrequently in affected dogs.4,8
Immature dogs with necrotizing fasciitis may develop subperiosteal abscesses.3 These abscesses may develop secondary to extension of osteomyelitis and subsequent breach of the periosteum, leading to necrotizing fasciitis or vice versa.3 The lesions around and involving the left femur of the dog of the present report were similar to previously reported subperiosteal abscesses in puppies with necrotizing fasciitis.3
The rapid progression of infection necessitates rapid and aggressive treatment before the results of bacterial culture and antimicrobial susceptibility testing and histologic evaluation are available.4,7 Necrotizing fasciitis can result in shock, disseminated intravascular coagulation, organ dysfunction, and death.3,8 Complete surgical debridement of affected tissues is required, and limb amputation may be needed.4 Medical intervention as the sole treatment for necrotizing fasciitis is ineffective because of the inadequate delivery of antimicrobials to the poorly perfused or necrotic tissue.4 As a result, necrotic tissue continues to be a nidus of infection.4
During surgery, the classic finding in cases of necrotizing fasciitis is easy separation of fascia from adjacent tissue by blunt dissection.4,7 This characteristic was observed during necropsy in the case described in this report. During surgery, tissue or swab samples should be collected from various affected areas, including the leading edge of infection, for histologic evaluation, bacterial culture and antimicrobial susceptibility testing, Gram staining, and cytologic evaluation, given that the center of the lesion may contain secondary invading organisms.7
In addition to surgical debridement, treatment of affected dogs with broad-spectrum antimicrobials (eg, penicillin or aminopenicillin, aminoglycoside, and clindamycin) is recommended while waiting for results of bacterial culture and antimicrobial susceptibility testing.1,4,8 The cause of necrotizing fasciitis in most dogs is infection with S canis; however, broad-spectrum antimicrobial coverage is recommended in case infection is caused by agents other than streptococci or because secondary bacterial infections are present. Treatment with fluoroquinolones is not advised because these drugs may enhance the pathogenicity of S canis by bacteriophage induction.2,4,8
Necrotizing fasciitis in cats has also been infrequently reported9,10; however, in most cases, the disease is similar to that described in dogs. In addition to S canis, Prevotella bivia, Acinetobacter baumannii, and Streptococcus pneumoniae have been isolated from samples obtained from cats with necrotizing fasciitis.9–11 Enterococcus faecium, Staphylococcus epidermidis, and E coli were isolated from a cat with Fournier's gangrene, which is a type of necrotizing fasciitis of the genital, perianal, and perineal regions.12 As in dogs, most reports of necrotizing fasciitis in cats have been sporadic; however, there is a report13 describing an outbreak of necrotizing fasciitis caused by S canis in shelter cats.
Necrotizing fasciitis should be considered when an ill animal has signs of soft tissue pain more severe than those expected on the basis of the gross appearance of the painful region. This condition should be a differential diagnosis for cellulitis because rapid treatment is required. The extent of such infection may not be fully revealed until surgical exploration is undertaken.
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