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Emergency and Acute Medicine – Skin and Soft Tissue Abscess
Overview and Definition
A skin or soft tissue abscess is a localized collection of pus that is encapsulated by inflamed tissue. Abscesses may develop anywhere on the body and vary widely in size, depth, and microbiology depending on location and patient risk factors. Variants include furuncles, which originate from infected hair follicles and commonly affect the back, axillae, and lower extremities, and carbuncles, which are larger, deeper, and more extensive infections.
Special anatomic locations have distinct considerations. Mammalian bites are typically polymicrobial. Breast abscesses may occur during lactation (puerperal) or due to duct ectasia, with differing microbial patterns. Hidradenitis suppurativa involves chronic abscess formation in apocrine gland–bearing areas such as the groin and scalp. Pilonidal abscesses arise from epithelial disruption in the gluteal cleft, while Bartholin abscesses result from duct obstruction. Perirectal abscesses originate from anal crypts and frequently require operative management. Other important entities include pyomyositis, abscesses related to IV drug use, paronychia, and felons of the distal finger pulp.
Etiology and Risk Factors
Abscess formation usually follows a break in the skin, obstruction of sebaceous or sweat glands, or inflammation of hair follicles. Most abscesses are bacterial, with microbiology reflecting local skin flora. Staphylococcus aureus is the most common pathogen, and community-acquired MRSA is frequently implicated.
Some abscesses may be sterile, particularly in individuals who inject chemical irritants intravenously. Risk factors include immunosuppression, soft tissue trauma, mammalian or human bites, tissue ischemia, IV drug use, and inflammatory bowel disease, particularly in perirectal infections.
Clinical Presentation
Local findings typically include erythema, warmth, swelling, tenderness, and fluctuance. Surrounding cellulitis is common, and regional lymphadenopathy or lymphangitis may occur. Systemic symptoms are often absent in uncomplicated cases. However, patients with extensive infection, necrotizing soft tissue involvement, or bacteremia may present with fever, rigors, hypotension, or altered mental status, indicating sepsis.
History and Physical Examination
History should address prior abscesses, which raise suspicion for MRSA, as well as immunosuppression, medication use (such as chronic steroids or chemotherapy), IV drug use, and recent animal or human bites.
Physical examination focuses on defining the location, size, and depth of infection and identifying associated cellulitis, subcutaneous air, or involvement of deep structures. Abscesses involving high-risk areas—such as the face, neck, hands, feet, perirectal region, or genitalia—require heightened caution and often specialty consultation.
Essential Workup
Diagnosis is primarily clinical. Gram stain and routine cultures are not necessary for simple abscesses in otherwise healthy individuals. Wound cultures may be useful when systemic antibiotics are planned, in recurrent infections to document MRSA, in immunocompromised hosts, in abscesses involving the face or hand, or when initial therapy fails.
Diagnostic Testing
Routine laboratory testing is generally unnecessary. Blood glucose measurement may be helpful when undiagnosed diabetes or diabetic ketoacidosis is suspected. In febrile or systemically ill patients, or those with recent IV drug use, blood cultures, lactate, renal function tests, and creatine kinase (if myositis is suspected) are appropriate.
Bedside ultrasound is valuable for differentiating cellulitis from abscess. CT or MRI may be needed to assess deep tissue involvement, while plain radiographs can detect gas in tissue planes.
Differential Diagnosis
Conditions that may mimic abscess include cellulitis, necrotizing fasciitis, hematoma, cysts, and aneurysm, particularly in IV drug users.
Initial Stabilization
Patients with signs of sepsis require prompt IV access, oxygen, crystalloid resuscitation, blood cultures, lactate measurement, and early broad-spectrum antibiotics with MRSA coverage. Rapid source control through drainage is essential.
Definitive Management
Incision and drainage is the cornerstone of abscess treatment. The incision must be sufficiently deep to allow complete evacuation, and elliptical incisions help prevent premature closure. Loculations should be gently broken up, and the cavity irrigated thoroughly.
Loose packing is recommended for abscesses larger than 5 cm, in patients with significant comorbidities, or when abscesses involve high-risk locations. For small, uncomplicated abscesses, routine packing is not always necessary.
Routine antibiotics are not required after drainage of uncomplicated abscesses. Antibiotic therapy is indicated in cases of systemic illness, significant cellulitis, facial abscesses with risk of cavernous sinus drainage, mammalian bites, immunocompromised patients, and perirectal abscesses, which generally require operative management.
The loop drainage technique offers a less invasive alternative that facilitates ongoing drainage, simplifies wound care, and often avoids repeat emergency department visits.
Pediatric Considerations
Incision and drainage are painful procedures in children and frequently require procedural sedation and adequate analgesia.
Antibiotic Therapy
Antibiotic selection should be guided by local resistance patterns. Oral agents are used for moderate associated cellulitis, while intravenous antibiotics are reserved for systemic illness or extensive infection. MRSA-active agents are commonly required, and broader coverage is necessary for bites or facial infections.
Disposition and Follow-Up
Admission is indicated for patients with sepsis, immunocompromised status with significant cellulitis, perirectal involvement, or abscesses requiring operative debridement.
Most patients with uncomplicated abscesses can be discharged after incision and drainage with close outpatient follow-up.
Follow-Up Care
Patients should return in 24–48 hours for wound reassessment and packing removal if used. Warm soaks are recommended for several days after packing removal to promote continued drainage.
Clinical Pearls and Pitfalls
Recurrent abscesses should prompt consideration of community-acquired MRSA. Adequate pain control is essential during drainage procedures. Always assess for deeper infections such as tenosynovitis or deep fascial space involvement, particularly in hand infections.
Overview and Definition
A skin or soft tissue abscess is a localized collection of pus that is encapsulated by inflamed tissue. Abscesses may develop anywhere on the body and vary widely in size, depth, and microbiology depending on location and patient risk factors. Variants include furuncles, which originate from infected hair follicles and commonly affect the back, axillae, and lower extremities, and carbuncles, which are larger, deeper, and more extensive infections.
Special anatomic locations have distinct considerations. Mammalian bites are typically polymicrobial. Breast abscesses may occur during lactation (puerperal) or due to duct ectasia, with differing microbial patterns. Hidradenitis suppurativa involves chronic abscess formation in apocrine gland–bearing areas such as the groin and scalp. Pilonidal abscesses arise from epithelial disruption in the gluteal cleft, while Bartholin abscesses result from duct obstruction. Perirectal abscesses originate from anal crypts and frequently require operative management. Other important entities include pyomyositis, abscesses related to IV drug use, paronychia, and felons of the distal finger pulp.
Etiology and Risk Factors
Abscess formation usually follows a break in the skin, obstruction of sebaceous or sweat glands, or inflammation of hair follicles. Most abscesses are bacterial, with microbiology reflecting local skin flora. Staphylococcus aureus is the most common pathogen, and community-acquired MRSA is frequently implicated.
Some abscesses may be sterile, particularly in individuals who inject chemical irritants intravenously. Risk factors include immunosuppression, soft tissue trauma, mammalian or human bites, tissue ischemia, IV drug use, and inflammatory bowel disease, particularly in perirectal infections.
Clinical Presentation
Local findings typically include erythema, warmth, swelling, tenderness, and fluctuance. Surrounding cellulitis is common, and regional lymphadenopathy or lymphangitis may occur. Systemic symptoms are often absent in uncomplicated cases. However, patients with extensive infection, necrotizing soft tissue involvement, or bacteremia may present with fever, rigors, hypotension, or altered mental status, indicating sepsis.
History and Physical Examination
History should address prior abscesses, which raise suspicion for MRSA, as well as immunosuppression, medication use (such as chronic steroids or chemotherapy), IV drug use, and recent animal or human bites.
Physical examination focuses on defining the location, size, and depth of infection and identifying associated cellulitis, subcutaneous air, or involvement of deep structures. Abscesses involving high-risk areas—such as the face, neck, hands, feet, perirectal region, or genitalia—require heightened caution and often specialty consultation.
Essential Workup
Diagnosis is primarily clinical. Gram stain and routine cultures are not necessary for simple abscesses in otherwise healthy individuals. Wound cultures may be useful when systemic antibiotics are planned, in recurrent infections to document MRSA, in immunocompromised hosts, in abscesses involving the face or hand, or when initial therapy fails.
Diagnostic Testing
Routine laboratory testing is generally unnecessary. Blood glucose measurement may be helpful when undiagnosed diabetes or diabetic ketoacidosis is suspected. In febrile or systemically ill patients, or those with recent IV drug use, blood cultures, lactate, renal function tests, and creatine kinase (if myositis is suspected) are appropriate.
Bedside ultrasound is valuable for differentiating cellulitis from abscess. CT or MRI may be needed to assess deep tissue involvement, while plain radiographs can detect gas in tissue planes.
Differential Diagnosis
Conditions that may mimic abscess include cellulitis, necrotizing fasciitis, hematoma, cysts, and aneurysm, particularly in IV drug users.
Initial Stabilization
Patients with signs of sepsis require prompt IV access, oxygen, crystalloid resuscitation, blood cultures, lactate measurement, and early broad-spectrum antibiotics with MRSA coverage. Rapid source control through drainage is essential.
Definitive Management
Incision and drainage is the cornerstone of abscess treatment. The incision must be sufficiently deep to allow complete evacuation, and elliptical incisions help prevent premature closure. Loculations should be gently broken up, and the cavity irrigated thoroughly.
Loose packing is recommended for abscesses larger than 5 cm, in patients with significant comorbidities, or when abscesses involve high-risk locations. For small, uncomplicated abscesses, routine packing is not always necessary.
Routine antibiotics are not required after drainage of uncomplicated abscesses. Antibiotic therapy is indicated in cases of systemic illness, significant cellulitis, facial abscesses with risk of cavernous sinus drainage, mammalian bites, immunocompromised patients, and perirectal abscesses, which generally require operative management.
The loop drainage technique offers a less invasive alternative that facilitates ongoing drainage, simplifies wound care, and often avoids repeat emergency department visits.
Pediatric Considerations
Incision and drainage are painful procedures in children and frequently require procedural sedation and adequate analgesia.
Antibiotic Therapy
Antibiotic selection should be guided by local resistance patterns. Oral agents are used for moderate associated cellulitis, while intravenous antibiotics are reserved for systemic illness or extensive infection. MRSA-active agents are commonly required, and broader coverage is necessary for bites or facial infections.
Disposition and Follow-Up
Admission is indicated for patients with sepsis, immunocompromised status with significant cellulitis, perirectal involvement, or abscesses requiring operative debridement.
Most patients with uncomplicated abscesses can be discharged after incision and drainage with close outpatient follow-up.
Follow-Up Care
Patients should return in 24–48 hours for wound reassessment and packing removal if used. Warm soaks are recommended for several days after packing removal to promote continued drainage.
Clinical Pearls and Pitfalls
Recurrent abscesses should prompt consideration of community-acquired MRSA. Adequate pain control is essential during drainage procedures. Always assess for deeper infections such as tenosynovitis or deep fascial space involvement, particularly in hand infections.
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