Necrotizing Fasciitis

Necrotizing fasciitis (NF) is a rapidly progressive, life-threatening bacterial infection of the subcutaneous soft tissues, specifically the superficial and deep fascial planes, with secondary necrosis of the overlying skin and underlying muscle. It is characterized by widespread fascial necrosis, microvascular thrombosis, and systemic inflammatory response syndrome (SIRS), often leading to septic shock and multiple organ dysfunction syndrome (MODS). In veterinary medicine, NF is most commonly reported in dogs and cats, and it represents a surgical emergency requiring aggressive debridement and antimicrobial therapy. The disease is classified into two main types: Type I, which is polymicrobial (mixed aerobic and anaerobic bacteria), and Type II, which is monomicrobial, typically caused by Streptococcus pyogenes (Group A beta-hemolytic streptococcus) in humans, but in animals, beta-hemolytic streptococci (e.g., Streptococcus canis) and other bacteria such as Escherichia coli, Staphylococcus aureus, and Clostridium species are frequently isolated. A distinct form, termed 'streptococcal toxic shock syndrome' (STSS), may accompany NF, characterized by hypotension, coagulopathy, and organ failure. The surgical significance lies in the need for early recognition, aggressive surgical debridement, and fasciotomy to halt the spread of infection, as medical therapy alone is insufficient. The disease can affect any body region, but the limbs, abdomen, and perineum are common sites. The condition is distinct from other necrotizing soft tissue infections (NSTIs) such as clostridial myonecrosis (gas gangrene) and cellulitis, which are less invasive and do not primarily involve fascial planes. The diagnosis is primarily clinical, supported by imaging and laboratory findings, but definitive confirmation requires surgical exploration and histopathology. Prompt surgical intervention is critical, as delayed debridement is associated with high mortality rates, reported to be 50-80% in veterinary patients.

Necrotizing fasciitis is caused by bacterial invasion of the subcutaneous tissues and fascial planes, typically following a breach in the skin barrier. The most common portals of entry include traumatic wounds (e.g., bites, lacerations, puncture wounds, surgical incisions), burns, and injection sites. In some cases, the source of infection may be hematogenous spread from a distant site, or it may be idiopathic with no obvious entry wound. The causative organisms are often part of the normal skin flora or environmental contaminants. In dogs, Streptococcus canis (a Lancefield group G beta-hemolytic streptococcus) is the most frequently isolated pathogen, followed by Escherichia coli, Staphylococcus aureus, and various anaerobes such as Bacteroides and Clostridium species. In cats, similar organisms are implicated, but Pasteurella multocida is also a common isolate. Polymicrobial infections (Type I NF) are more common in immunocompromised patients or those with comorbidities such as diabetes mellitus, chronic renal failure, or immunosuppressive therapy. Monomicrobial infections (Type II NF) are typically more aggressive and rapidly progressive. The bacteria produce exotoxins and enzymes (e.g., streptolysin S, hyaluronidase, streptokinase, and proteases) that facilitate tissue destruction, spread along fascial planes, and evade the host immune response. Superantigens, such as streptococcal pyrogenic exotoxins, trigger a massive release of pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6), leading to systemic toxicity and SIRS. The infection rapidly spreads along the deep fascia, causing thrombosis of penetrating blood vessels, which results in ischemic necrosis of the overlying skin and underlying muscle. The exact trigger for the transition from localized infection to fulminant NF is not fully understood, but it is likely related to a combination of bacterial virulence factors, host immune status, and local tissue conditions (e.g., hypoxia, edema, trauma).

Necrotizing fasciitis is a relatively rare but devastating condition in veterinary medicine, with a reported incidence of less than 1% of all wound infections. It is most commonly diagnosed in dogs, with a slight male predisposition, and can occur at any age, but middle-aged to older animals (median age 6-10 years) are more frequently affected. Large and giant breeds, such as Golden Retrievers, Labrador Retrievers, and German Shepherd Dogs, may be overrepresented, possibly due to their active lifestyles and higher risk of trauma. Cats are less commonly affected, but cases have been reported, particularly in outdoor cats with bite wounds. There is no clear breed predisposition in cats. The condition is more prevalent in immunocompromised individuals, including those with diabetes mellitus, hyperadrenocorticism, or those receiving long-term corticosteroid or chemotherapy. In dogs, a specific association with streptococcal toxic shock syndrome has been noted, and outbreaks have been reported in kennels, suggesting possible contagious transmission. The mortality rate in veterinary patients is high, ranging from 50% to 80%, despite aggressive treatment. Early recognition and surgical intervention significantly improve survival, with mortality rates dropping to less than 20% if surgery is performed within 24 hours of presentation. The disease is more common in warm climates and during summer months, possibly due to increased outdoor activity and higher bacterial loads in the environment. However, no definitive seasonal pattern has been established in veterinary literature.

The pathophysiology of necrotizing fasciitis is a complex interplay between bacterial virulence factors and the host immune response. The infection typically begins with bacterial inoculation into the subcutaneous tissue, often through a break in the skin. The bacteria adhere to and colonize the tissue, then produce enzymes and toxins that facilitate spread along the superficial and deep fascial planes. Hyaluronidase breaks down hyaluronic acid in the extracellular matrix, allowing rapid lateral spread. Streptokinase and staphylokinase activate plasminogen, leading to fibrinolysis and further tissue destruction. Proteases degrade collagen and other structural proteins, causing liquefactive necrosis of the fascia. The bacteria also produce exotoxins, such as streptolysin O and S, which are cytotoxic to host cells, including neutrophils, macrophages, and endothelial cells. This leads to microvascular thrombosis, which compromises blood flow to the overlying skin and underlying muscle, resulting in ischemic necrosis. The ischemic tissue provides an ideal environment for anaerobic bacterial growth, perpetuating the cycle of necrosis. The release of superantigens, such as streptococcal pyrogenic exotoxins (SpeA, SpeB, SpeC), causes non-specific activation of T lymphocytes, leading to a massive release of pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6, IL-8). This 'cytokine storm' results in systemic inflammatory response syndrome (SIRS), characterized by fever or hypothermia, tachycardia, tachypnea, and leukocytosis or leukopenia. The systemic effects include vasodilation, increased capillary permeability, and myocardial depression, leading to hypotension, shock, and multiple organ dysfunction syndrome (MODS). Coagulopathy may develop due to disseminated intravascular coagulation (DIC), further compromising tissue perfusion. The rapid progression of the disease is due to the synergistic effects of bacterial toxins and the host's inflammatory response, which can lead to death within hours to days if not aggressively treated.

Several intrinsic and extrinsic factors predispose animals to necrotizing fasciitis. Intrinsic factors include immunocompromised states such as diabetes mellitus, hyperadrenocorticism, chronic renal failure, and immunosuppressive drug therapy (e.g., corticosteroids, cyclosporine). Age and breed may also play a role, with older animals and certain breeds (e.g., Golden Retrievers) being more susceptible. Obesity and malnutrition can impair immune function and wound healing, increasing the risk of infection. Extrinsic factors include any breach in the skin barrier, such as traumatic wounds (bites, lacerations, puncture wounds), surgical incisions, burns, and injection sites. Poor wound hygiene, delayed wound care, and contamination with soil or feces increase the risk. Environmental factors, such as high temperature and humidity, may promote bacterial growth. In addition, the presence of foreign bodies (e.g., grass awns, splinters) can serve as a nidus for infection. Prior antibiotic therapy may select for resistant organisms, and the use of non-steroidal anti-inflammatory drugs (NSAIDs) has been suggested to mask early signs of infection, leading to delayed diagnosis. Finally, stress and overcrowding, as seen in kennels, may increase the risk of contagious spread of virulent streptococcal strains.

The clinical signs of necrotizing fasciitis are often rapidly progressive and severe. Early signs may be subtle and include localized pain, swelling, erythema, and warmth at the site of infection. The animal may be lethargic, febrile (or hypothermic in severe cases), and anorexic. As the disease progresses, the skin over the affected area becomes discolored (purple or black), with bullae or vesicles, and may develop a characteristic 'dishwater' discharge. The area is extremely painful, and the animal may exhibit lameness if a limb is affected. Crepitus may be palpable if gas-producing organisms are present. Systemic signs include tachycardia, tachypnea, pale mucous membranes, prolonged capillary refill time, and signs of shock. In advanced stages, the animal may become recumbent, obtunded, and develop coagulopathy (petechiae, ecchymoses) and multiple organ dysfunction. The infection can spread rapidly, with the affected area expanding visibly within hours. In some cases, the skin may slough off, revealing necrotic fascia and muscle. The severity of clinical signs is often disproportionate to the external appearance of the wound, which is a key diagnostic clue. The disease can affect any body region, but the limbs, abdomen, and perineum are common sites. In dogs, streptococcal toxic shock syndrome may accompany NF, characterized by acute onset of fever, vomiting, diarrhea, and shock, with or without a visible wound.

The differential diagnoses for necrotizing fasciitis include other necrotizing soft tissue infections and conditions that cause similar clinical signs. These include: 1) Cellulitis: A bacterial infection of the skin and subcutaneous tissue that is less invasive and does not typically cause fascial necrosis. It responds to antibiotics and does not require surgical debridement. 2) Abscess: A localized collection of pus that is walled off and can be drained. It is less rapidly progressive and does not cause systemic signs unless ruptured. 3) Clostridial myonecrosis (gas gangrene): A deep muscle infection caused by Clostridium species, characterized by severe pain, crepitus, and rapid tissue destruction. It is distinguished by the presence of gas in muscle tissue on radiographs and the involvement of muscle rather than fascia. 4) Pyoderma gangrenosum: A rare, sterile neutrophilic dermatosis that can mimic NF but is not infectious and does not respond to antibiotics. 5) Snakebite envenomation: Can cause severe local tissue necrosis and systemic signs, but there is a history of snakebite and characteristic fang marks. 6) Burns: Thermal or chemical burns can cause tissue necrosis and secondary infection, but the history and appearance are distinct. 7) Trauma with severe contusions: Can cause tissue swelling and pain, but without infection, systemic signs are less severe. 8) Neoplasia: Some tumors, such as squamous cell carcinoma or soft tissue sarcomas, can become necrotic and infected, but they are typically slower-growing and have a different clinical course. 9) Immune-mediated diseases: Such as vasculitis or panniculitis, can cause skin necrosis and systemic signs, but they are not infectious and require immunosuppressive therapy. 10) Foreign body reactions: Can cause localized inflammation and infection, but are usually less rapidly progressive. Definitive diagnosis of NF requires surgical exploration and histopathology, which will show fascial necrosis, microvascular thrombosis, and abundant bacteria.

The diagnostic algorithm for necrotizing fasciitis is based on rapid clinical assessment and confirmation. The following steps are recommended: 1) Clinical suspicion: Any animal with a rapidly progressive, painful soft tissue infection, especially with systemic signs, should be suspected of having NF. 2) Physical examination: Look for signs of skin discoloration, bullae, crepitus, and severe pain. The presence of pain out of proportion to the external appearance is a key finding. 3) Laboratory tests: Complete blood count (CBC), serum biochemistry, and coagulation profile. Leukocytosis or leukopenia, elevated C-reactive protein (CRP), and elevated creatine kinase (CK) may be present. Blood cultures should be obtained. 4) Imaging: Radiographs may show gas in the soft tissues, but this is not always present. Ultrasound can reveal thickening of the fascia and fluid accumulation. Computed tomography (CT) or magnetic resonance imaging (MRI) can provide detailed images of the extent of tissue involvement, but these may not be readily available in an emergency setting. 5) Surgical exploration: The gold standard for diagnosis is surgical exploration under general anesthesia. The affected area is incised, and the fascia is examined. Findings include grayish, necrotic fascia that easily separates from the surrounding tissue, and a thin, murky fluid ('dishwater' pus). Tissue samples should be collected for aerobic and anaerobic culture, as well as histopathology. 6) Histopathology: Frozen section or permanent sections can confirm the diagnosis by showing necrosis of the fascia, microvascular thrombosis, and inflammatory infiltrate. 7) Molecular diagnostics: Polymerase chain reaction (PCR) can be used to identify specific pathogens, such as Streptococcus canis. 8) Rapid diagnostic tests: In human medicine, the LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score is used, but this has not been validated in veterinary medicine. The diagnostic algorithm should be performed rapidly, as any delay in surgical intervention increases mortality.

Laboratory findings in necrotizing fasciitis are non-specific but support the diagnosis and assess the severity of systemic involvement. Complete blood count (CBC) often reveals leukocytosis with a left shift, or leukopenia in severe cases, indicating a poor prognosis. Anemia may be present due to hemolysis or blood loss. Thrombocytopenia may occur due to consumption or DIC. Serum biochemistry may show elevated creatine kinase (CK) due to muscle necrosis, elevated liver enzymes (ALT, AST) due to hepatic hypoxia, and elevated renal parameters (BUN, creatinine) due to acute kidney injury. Blood glucose may be elevated due to stress or diabetes, or decreased in septic shock. Electrolyte imbalances, such as hyponatremia and hyperkalemia, may be present. Coagulation panel (PT, aPTT, fibrinogen, D-dimer) may reveal prolonged clotting times and elevated D-dimer, indicating DIC. Blood gas analysis may show metabolic acidosis with elevated lactate, reflecting tissue hypoperfusion. Inflammatory biomarkers, such as C-reactive protein (CRP) and serum amyloid A (SAA), are typically markedly elevated. Synovial fluid analysis is not typically performed unless there is joint involvement, but if the infection has spread to a joint, the fluid will be purulent with a high nucleated cell count (often >50,000 cells/µL) and degenerate neutrophils. Blood cultures are positive in approximately 50% of cases, and the most common isolate is Streptococcus canis. Urinalysis may show proteinuria, hematuria, or casts due to renal involvement. It is important to note that laboratory findings may be normal in the early stages, and a high index of suspicion is required.

Imaging modalities are useful in the diagnosis and assessment of necrotizing fasciitis, but they should not delay surgical exploration. Radiography: Plain radiographs of the affected area may show soft tissue swelling and gas in the subcutaneous tissues, which appears as radiolucent areas. Gas is present in approximately 30-50% of cases, and its absence does not rule out NF. Radiographs can also help identify foreign bodies or fractures. Ultrasonography: Ultrasound can reveal thickening of the subcutaneous tissues and fascia, with fluid accumulation along fascial planes. It is a useful bedside tool, but it is operator-dependent and may not be sensitive enough to detect early changes. Computed Tomography (CT): CT is highly sensitive for detecting gas, fluid collections, and tissue necrosis. It can delineate the extent of the infection and help plan surgical debridement. CT findings include subcutaneous emphysema, fascial thickening, and abscess formation. Magnetic Resonance Imaging (MRI): MRI provides excellent soft tissue contrast and can show deep fascial involvement, muscle edema, and necrosis. It is the most sensitive imaging modality for NF, but it is time-consuming and may not be available in an emergency setting. In veterinary medicine, MRI is often not feasible due to the need for general anesthesia and the critical condition of the patient. Fluoroscopy or angiography is rarely used. In summary, imaging can support the diagnosis, but surgical exploration remains the definitive diagnostic and therapeutic intervention.

Cytology and histopathology are essential for confirming the diagnosis of necrotizing fasciitis and identifying the causative organisms. Cytology: Fine-needle aspiration of the affected tissue or fluid may be performed. The aspirate is typically purulent, with a high nucleated cell count, predominantly degenerate neutrophils. Bacteria may be seen intracellularly or extracellularly, and their morphology (cocci, rods) can guide initial antimicrobial therapy. Gram staining can differentiate between Gram-positive and Gram-negative organisms. However, cytology may be non-diagnostic if the sample is not representative. Histopathology: Surgical biopsy of the affected fascia and subcutaneous tissue is the gold standard. Grossly, the fascia appears grayish, necrotic, and easily separated from the surrounding tissue. Microscopic examination reveals extensive necrosis of the superficial and deep fascia, with microvascular thrombosis, hemorrhage, and a dense inflammatory infiltrate composed of neutrophils, macrophages, and lymphocytes. The overlying skin may show epidermal necrosis and dermal edema. Special stains, such as Gram stain, can identify bacteria within the tissue. Immunohistochemistry or PCR can be used to specifically identify pathogens, such as Streptococcus canis. Histopathology also helps differentiate NF from other conditions, such as cellulitis or myonecrosis. It is important to submit multiple tissue samples from the leading edge of the infection, as the center may be necrotic and devoid of viable cells.

The treatment of necrotizing fasciitis requires a multi-modal approach, with aggressive surgical debridement as the cornerstone. The following steps are essential: 1) Preoperative stabilization: The patient is often in septic shock and requires aggressive fluid resuscitation with crystalloids (e.g., Lactated Ringer's solution at 20-30 mL/kg bolus, then 10-20 mL/kg/h) and colloids (e.g., hetastarch) if needed. Vasopressors (e.g., norepinephrine) may be required if hypotension persists. Broad-spectrum antimicrobial therapy should be initiated immediately after blood cultures are obtained. A combination of a beta-lactam (e.g., ampicillin-sulbactam 20 mg/kg IV q8h) and an aminoglycoside (e.g., gentamicin 6-8 mg/kg IV q24h) or a fluoroquinolone (e.g., enrofloxacin 10 mg/kg IV q24h) is often used, with the addition of metronidazole (10 mg/kg IV q12h) for anaerobic coverage. Analgesia is provided with opioids (e.g., hydromorphone 0.05-0.1 mg/kg IV q4-6h) and local blocks. 2) Surgical debridement: The patient is anesthetized, and the entire affected area is clipped and prepared aseptically. The surgical approach involves making a generous incision through the skin and subcutaneous tissue to expose the deep fascia. All necrotic tissue, including fascia, subcutaneous fat, and non-viable skin, is excised. The debridement should extend beyond the visible margins of necrosis, as the infection spreads along fascial planes. The wound is left open, and a second-look surgery is performed within 24-48 hours to assess the viability of the remaining tissue and debride further if necessary. In some cases, multiple debridements are required. 3) Wound management: After debridement, the wound is managed as an open wound, with wet-to-dry dressings or negative-pressure wound therapy (NPWT) to promote granulation tissue formation. The wound is lavaged with sterile saline or dilute chlorhexidine (0.05%) during dressing changes. 4) Adjunctive therapies: Hyperbaric oxygen therapy has been used in human medicine, but its availability in veterinary medicine is limited. The use of intravenous immunoglobulin (IVIG) has been suggested to neutralize superantigens, but its efficacy is unproven. 5) Postoperative care: The patient requires intensive monitoring in an ICU setting. Fluid therapy, antimicrobials, and analgesics are continued. Nutritional support is provided, often via feeding tube if the animal is anorexic. Physical therapy may be initiated once the wound is stable. 6) Reconstruction: Once the infection is controlled and granulation tissue is present, the wound may be closed surgically, either by primary closure, skin grafts, or flaps, depending on the size and location. The timing of reconstruction is critical, as premature closure can lead to recurrence of infection.

The prognosis for necrotizing fasciitis is guarded to poor, with reported mortality rates of 50-80% in dogs and cats. However, early and aggressive surgical intervention significantly improves the outcome. Factors associated with a better prognosis include: early presentation (within 24 hours of onset), absence of systemic signs, and successful debridement with control of infection. Negative prognostic indicators include: delayed diagnosis, presence of septic shock, coagulopathy, multiple organ dysfunction, and the need for multiple debridements. The extent of tissue involvement also affects the prognosis, as extensive limb involvement may require amputation, which carries its own morbidity. In survivors, the recovery period is prolonged, and there may be significant scarring and loss of function. The long-term prognosis for animals that survive the acute phase is generally good, with many returning to normal function, especially if the affected area is small and reconstruction is successful. However, the risk of recurrence is low but possible. It is important to provide owners with realistic expectations and discuss the possibility of euthanasia in severe cases where the animal is suffering and the prognosis is grave.

Follow-up care for necrotizing fasciitis is intensive and prolonged. In the immediate postoperative period, the patient is monitored in the ICU for signs of sepsis, organ dysfunction, and wound complications. Vital parameters (heart rate, respiratory rate, blood pressure, temperature, urine output) are monitored frequently. Blood work (CBC, biochemistry, lactate, coagulation) is repeated daily or as needed. The wound is inspected and dressed daily, and a second-look surgery is performed within 24-48 hours to assess tissue viability. Subsequent debridements are performed as necessary. Once the infection is controlled, the wound is managed with dressings, and the frequency of dressing changes is gradually reduced as granulation tissue forms. Suture removal, if any, is typically at 10-14 days, but in open wounds, there are no sutures. Serial radiographs or ultrasound may be used to monitor for deep tissue involvement. The animal is discharged from the hospital when it is stable, eating, and the wound is manageable at home. The owner is instructed on wound care, including cleaning and dressing changes. Antibiotics are continued for 1-2 weeks after clinical resolution, but the duration may be longer if there is residual infection. Physical rehabilitation is initiated to maintain joint mobility and muscle mass, especially if a limb is affected. This may include passive range of motion exercises, swimming, and controlled leash walks. The animal is re-examined at 1, 2, 4, 8, and 12 weeks post-discharge to monitor wound healing and overall recovery. Long-term follow-up may be needed to address complications such as scarring, contracture, or chronic pain. The owner should be advised to monitor for any signs of recurrence, such as swelling, redness, or pain, and seek immediate veterinary attention if these occur.

Clinical Pearls: 1) Maintain a high index of suspicion for NF in any animal with a rapidly progressive, painful soft tissue infection, especially if the pain is out of proportion to the external appearance. 2) Early surgical exploration is both diagnostic and therapeutic; do not wait for imaging or laboratory confirmation. 3) The 'finger test' is useful: under anesthesia, a blunt instrument (e.g., a hemostat) is inserted into the wound; if it easily dissects along the fascial plane, NF is likely. 4) The presence of gas on radiographs is a late sign and is not always present. 5) Aggressive debridement is essential; leave the wound open and plan for a second-look surgery. 6) Use broad-spectrum antimicrobials initially, then tailor based on culture and sensitivity. 7) Provide aggressive fluid resuscitation and vasopressor support for septic shock. 8) Consider the use of negative-pressure wound therapy to accelerate granulation tissue formation. 9) In cases of limb involvement, early amputation may be life-saving if the infection is uncontrollable. 10) Communicate clearly with the owner about the grave prognosis and the need for multiple surgeries. Pitfalls: 1) Delaying surgery while awaiting imaging or laboratory results. 2) Inadequate debridement, leaving behind necrotic tissue. 3) Closing the wound prematurely, leading to recurrence. 4) Using only medical therapy without surgical intervention. 5) Underestimating the severity of the infection based on the external appearance. 6) Failing to monitor for systemic complications such as DIC and MODS. 7) Inadequate analgesia, leading to stress and worsening of the condition. 8) Not obtaining cultures before starting antibiotics, which can hinder identification of the causative organism. 9) Using NSAIDs, which may mask fever and pain, delaying diagnosis. 10) Failing to provide adequate nutritional support during the recovery period.

The following drug protocols are based on Plumb's Veterinary Drug Handbook and current veterinary literature. Antimicrobials: 1) Ampicillin-sulbactam (Unasyn) 20 mg/kg IV q8h – provides broad-spectrum coverage including Gram-positive, Gram-negative, and anaerobes. 2) Gentamicin 6-8 mg/kg IV q24h – for Gram-negative coverage; monitor renal function. 3) Enrofloxacin (Baytril) 10 mg/kg IV q24h – alternative for Gram-negative coverage. 4) Metronidazole 10 mg/kg IV q12h – for anaerobic coverage. 5) Clindamycin 10 mg/kg IV q12h – effective against streptococci and anaerobes, and may inhibit toxin production. 6) In cases of MRSA, consider vancomycin (15 mg/kg IV q8h) or linezolid (10 mg/kg PO q12h). Analgesics: 1) Hydromorphone 0.05-0.1 mg/kg IV q4-6h – for severe pain. 2) Fentanyl CRI 2-5 µg/kg/h IV – for constant analgesia. 3) Morphine 0.5-1 mg/kg IM or IV q4-6h. 4) Ketamine CRI 0.5 mg/kg/h IV – as an adjunct for pain control. 5) Lidocaine CRI 25-50 µg/kg/min IV – for analgesia and anti-inflammatory effects. 6) NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h) may be used after the patient is stabilized and renal function is normal, but avoid in shock. Fluid therapy: 1) Lactated Ringer's solution (LRS) or Normosol-R at 20-30 mL/kg bolus, then 10-20 mL/kg/h. 2) Hetastarch (6% HES) 10-20 mL/kg IV over 1 hour, but use with caution due to risk of coagulopathy. Vasopressors: 1) Norepinephrine 0.05-0.5 µg/kg/min IV CRI – for refractory hypotension. 2) Vasopressin 0.5-2 mU/kg/min IV CRI – may be added. Other: 1) Human intravenous immunoglobulin (IVIG) 0.5-1 g/kg IV over 6-12 hours – may neutralize superantigens, but use is controversial. 2) Hyperbaric oxygen therapy – not widely available. 3) Nutritional support: enteral feeding via nasogastric or esophagostomy tube, using a high-protein diet. 4) Gastroprotectants: pantoprazole 1 mg/kg IV q12h – to prevent stress ulcers. 5) Antiemetics: maropitant 1 mg/kg SC q24h – if vomiting. 6) Heparin 75-100 U/kg SC q8h – for DIC prophylaxis, but monitor coagulation.

The veterinary literature on necrotizing fasciitis is limited to case reports and small case series. A landmark study by Naidoo et al. (2005) described 10 cases of NF in dogs, with Streptococcus canis being the most common isolate. The mortality rate was 60%, and early surgical debridement was associated with improved survival. Another study by Prescott et al. (1997) reported an outbreak of streptococcal toxic shock syndrome in a kennel, with NF in some dogs. A retrospective study by Weese et al. (2009) identified NF in 15 dogs and 5 cats, with a mortality rate of 70%. They emphasized the importance of aggressive surgical debridement and the use of clindamycin for toxin suppression. In human medicine, the LRINEC score has been validated for early diagnosis, but its use in veterinary medicine is not established. The Infectious Diseases Society of America (IDSA) guidelines for the management of skin and soft tissue infections recommend immediate surgical debridement for NF, and these principles are applicable to veterinary patients. The use of IVIG has been shown to reduce mortality in human streptococcal toxic shock syndrome, but its efficacy in animals is unproven. A recent systematic review by Broughton et al. (2020) on necrotizing soft tissue infections in dogs and cats concluded that early recognition and surgical intervention are the most critical factors for survival. They also highlighted the need for standardized reporting and prospective studies. Overall, the evidence supports a multimodal approach with aggressive surgery, broad-spectrum antimicrobials, and intensive supportive care.