Skin and soft tissue infections case file

Skin and soft tissue infections case file

Eugene C. Toy, MD, Barry C. Simon, MD, Terrence H. Liu, MD, MHP, Katrin Y. Takenaka, MD, Adam J. Rosh, MD, MS

Case 57

A 45-year-old man presents to the ED complaining of left shoulder pain. Past history includes numerous skin abscesses, hepatitis C and injection drug use. He injected black tar heroin into the left upper extremity 2 days ago. On examination the patient is in mild distress. There is a low-grade fever, the heart rate is 115 bpm and blood pressure is 120/60 mm Hg. The dorsum of the upper arm is erythematous, indurated and tender. There is no obvious area of fluctuance. Edema extends to the shoulder and pectoralis region of the trunk.

⯈ What is the most likely diagnosis?

⯈ What are the next diagnostic and treatment steps?

ANSWER TO CASE 57:

Skin and Soft Tissue Infections

Summary: This is an injection drug user with a fever and a skin and soft tissue infection (SSTI) of the upper extremity and shoulder.

• Most likely diagnosis: Soft tissue abscess from injection drug use. However, necrotizing soft tissue infection (NSTI) is a distinct possibility, and the differential diagnosis also includes cellulitis and septic shoulder joint.
• Next steps: Establish IV access. IV antibiotics are generally indicated when a SSTI produces a fever. Establish a definitive diagnosis as quickly as possible, beginning with a careful search for a pus pocket. If an abscess is found it must be drained. If not, NSTI remains a possibility and immediate surgical exploration is indicated. Search for signs of sepsis, and if present begin early goal directed therapy.

ANALYSIS

Objectives

1. Recognize the range of SSTIs, which can look remarkably similar on first inspection.
2. Become familiar with the usual pathogens responsible for SSTIs and the antimicrobial agents that are commonly used for empirical therapy.
3. Understand that NSTIs can be life threatening, rapidly progressive and difficult to diagnose.
4. Recognize the risk factors associated with necrotizing infections and with unusual pathogens.
5. Appreciate that uncomplicated abscesses often require only incision and drainage, and no antibiotics, for cure.

Considerations

SSTIs are among the most common problems seen in the ED, accounting for 3.4 million annual visits in the United States alone. There has been a recent rise in the incidence of these infections linked to the emergence of community-associated methicillin resistant Staphylococcus aureus. While simple abscesses predominate, there is a range of distinct SSTI types, which includes deep abscesses, nonpurulent cellulitis and NSTIs. NSTIs can be rapidly life-threatening and timely diagnosis is often difficult. SSTIs of all types are extremely common in injection drug users, and thus in emergency departments that serve an injection drug use population. Red flags can alert the astute clinician to a necrotizing infection as well as to unusual pathogens that require special antibiotics. To complicate matters, other diseases affecting the skin and underlying tissues can be confused with infection, particularly gout and other forms of arthritis and bursitis, allergic reactions to insect bites and deep vein thrombosis.

Diagnosis and management of SSTIs can be tricky. Different types of SSTIs, that require different approaches to management, can appear similar. While diagnostic tests such as bedside ultrasound, CT scan and blood lactate levels can be helpful, in most cases correct diagnosis relies solely on the bedside exam and judgment of the emergency physician. Many of these infections are primarily a surgical disease. Effective management often requires only the skillful administration of anesthetic and incision and drainage in the ED, but occasionally, immediate exploration and debridement in the operating room is required. Similarly, while judicious use of antibiotics is an important principal in the management of most simple SSTIs, serious SSTIs will occasionally cause sepsis syndrome, in which case immediate antibiotic administration and aggressive resuscitation is imperative.

Approach To:

Skin and Soft Tissue Infections

DEFINITIONS

SKIN AND SOFT TISSUE INFECTION (SSTI): An infection, usually bacterial, of the skin and/or underlying soft tissues.

NECROTIZING SKIN AND SOFT TISSUE INFECTION (NSTI): A rapidly spreading bacterial infection (monomicrobial or polymicrobial) of the soft tissue below the skin surface including fat, fascia (fasciitis), and muscle (myositis).

PURULENT (CULTURABLE) CELLULITIS: Infection and/or inflammatory changes of the skin surrounding a purulent focus (usually an abscess).

NONPURULENT (NON-CULTURABLE) CELLULITIS: An infection of the skin and underlying dermis without an identifiable purulent focus.

ERYSIPELAS: Nonpurulent cellulitis restricted to the superficial skin layers with a sharply demarcated border.

CLINICAL APPROACH

Diagnosis

Clinical evaluation of SSTIs always begins with a search for a pus pocket, because both the differential diagnosis and clinical management depend on whether or not there is pus (Figure 57–1). Circular infections (as opposed to circumferential) on the buttock, groin and lower extremity almost always harbor pus near the center. First look for a visible spot of purulence or necrosis. Then palpate carefully for fluctuance, which can be subtle. Fluctuance may be absent if the abscess is deep, as often occurs in the pannus of the buttock or thigh, or if the abscess is early in its course. Very deep intramuscular abscesses can occur with injection drug use. Bedside ultrasound, using a high frequency linear transducer, can identify deep abscesses that are not appreciated on physical examination. On ultrasound, the abscess cavity typically appears

Figure 57–1. Approach to the diagnosis and management of skin and soft tissue infections. NSTI, necrotizing skin and soft tissue infection; ∗ primarily surgical diseases.

anechoic (black with no echo). CT scan is considered the gold standard for abscess diagnosis, and is used to identify those near the neck, groin and perineum.

Spontaneous, superficial skin abscesses are called furuncles and patients often assume these are spider bites. Skin abscesses are usually caused by S aureus–over half by MRSA–and less commonly β-hemolytic streptococcal species. Abscesses associated with injection drug use, and those occurring near the perineum may contain gram negative and anaerobic bacteria. Abscesses are typically surrounded by a variable amount of cellulitis (so-called purulent cellulitis), and large abscesses may cause fever.

If an abscess is not present; the main diagnostic considerations are cellulitis versus NSTI (Figure 57–1).

Nonpurulent cellulitis tends to occur on the lower extremities in a circumferential pattern, often in an area of preexisting edema. The etiology is usually β-hemolytic streptococcal species, such as S pyogenes. Cellulitis may be associated with lymphangitis and fever. Erysipelas is a superficial, sharply demarcated cellulitis caused by S pyogenes that often occurs in elderly patients on the face or lower extremities, and causes fever and leukocytosis.

Cellulitis in certain settings is always considered high risk, either because it is caused by esoteric or resistant pathogens, or because of the likelihood of severe disease requiring admission or an operation. Infected puncture wounds of any kind are high risk and likely to involve deep structures like bone, joint or tendon, and to respond poorly to conventional antibiotics alone. Tenosynovitis, an orthopedic emergency, can complicate puncture wounds on the palmar hand and fingers. Diabetic foot ulcers, when infected, tend to harbor multiple resistant pathogens, can lead to NSTI, and generally require specialized podiatric care. Infected mammalian bite wounds, covered elsewhere in this textbook, are high risk, often harbor Pasteurella species or Eikinella (human bites) and generally require admission. Unusual pathogens that cause SSTIs in the setting of water exposure include Vibrio vulnificus, which often causes a necrotizing infection and sepsis, Erysipelothrix, and Aeromonas.

NSTIs are among the most feared infections in medicine. These infections typically spread rapidly along subcutaneous and muscular facial planes and produce toxins and trigger an intense cytokine response that lead to septic shock. Classically, NSTIs occur in the setting of devitalized tissue, such as from a shrapnel wound, and the etiology is polymicrobial, with C perfringens among the pathogens. A spontaneous, monomicrobial form of NSTI also occurs, typically caused by S pyogenes, but occasionally by Clostridial species or MRSA. Rapid diagnosis requires that the clinician be familiar with the risk factors for NSTI and red flags on physical examination (see Table 57–1).

An important risk factor for community onset necrotizing fasciitis is injection drug use, particularly subcutaneous and intramuscular injection (“skin popping”) of black tar heroin. Other infection patterns that should raise a red flag are neglected diabetic foot ulcers and infections of the perineum, particularly in men. Classical skin signs such as necrosis, bullae or crepitance are often absent. The Clostridial infections associated with injection drug use may produce dramatic tissue edema and extreme leukocytosis. The combination of extreme leukocytosis and hyponatremia is suggestive of an NSTI. Diagnostic imaging can be helpful. Plane x-ray and CT scan may demonstrate gas along facial planes or within muscle, or an unsuspected abscess may be seen. When NSTI is suspected, however, the best diagnostic approach is prompt surgical exploration. The diagnosis is made when subcutaneous devitalized tissue, muscle necrosis and “dishwater pus” are found.

The bacteriology of the major forms of SSTI, are listed in Table 57–2, along with recommended antibiotics.

Abbreviations: SSTI = skin and soft tissue infection; MRSA = methicillin-resistant Staphylococcus aureus; NSTI = necrotizing

skin and soft tissue infection.

Management

Abscesses require drainage. Management begins with providing complete analgesia for the procedure. Options include local anesthetic, regional nerve block, and procedural sedation. In most cases drainage is best accomplished by incision with a scalpel and exploration of the cavity with a clamp, although needle aspiration is a good option for small abscesses on the face. Delaying drainage for a follow up visit is rarely the right plan. Small abscesses do not require packing. Large abscesses should be packed and the packing can be changed at 24-hour, either upon emergency department follow-up or by the patient themselves. Most simple abscesses do not require any antibiotics after incision and drainage. Small and uncomplicated abscesses rarely cause fever. If fever is present in these patient alternative sources should be considered. Antibiotics should be reserved for complicated abscesses, defined as >5cm, having a large area of surrounding cellulitis, or occurring in an immunosuppressed host. Admission for IV antibiotics should be considered for large abscesses accompanied by fever. Staphylococcal coverage, including MRSA, is required. Recommended agents include trimethoprim-sulfamethoxazole for oral therapy and vancomycin for IV therapy.

Nonpurulent cellulitis requires antibiotics for cure. Most cases can be treated with oral antibiotics and elevation of the affected part. Good Streptococcal coverage is required, usually with a first generation cephalosporin. (Therapy for purulent cellulitis must cover Staphylococcus as well; see above.) Admission for IV antibiotics is usually required if there is fever, lymphangitis or poorly controlled diabetes.

The biggest challenge with NSTIs is timely diagnosis. Once the suspicion for necrotizing infection reaches a reasonable threshold, the emergency physician should immediately consult a surgeon and request operative exploration for both definitive diagnosis and treatment. Immediate broad-spectrum antibiotic therapy is also important, and must cover streptococcal species, anaerobes and MRSA. Good choices are vancomycin plus clindamycin or pipercillin-tazobactam. If signs of sepsis are present (hypotension or lactate >4 mg/dL), central access and early goal directed therapy should be initiated.

COMPREHENSION QUESTIONS

57.1 A 40-year-old woman complains of a spider bite on her leg. What is the most likely diagnosis and etiologic organism?

A. Spider bite from a dermonecrotic spider species

B. Impetigo from Group A Streptococcus

C. Abscess from a polymicrobial mix of species including Streptococcus milleri

D. Furuncle from methicillin-resistant S aureus

57.2 A 35-year-old HIV-positive injection drug user presents complaining of a hip abscess where he injects heroin. The temperature is 38.1°C and there is a 10 × 10 cm circular area of erythema and induration on the lateral buttock without fluctuance. Which is the correct management?

A. Prescribe oral cephalexin for cellulitis and instruct the patient to return in 24 hours to assess whether an abscess has developed.

B. Attempt needle aspiration at the center of the infection, and if negative, cover with oral antibiotics.

C. Search for an abscess with bedside ultrasound and establish an IV in anticipation of a drainage procedure and admission for IV antibiotics.

D. Consult a surgeon immediately for suspected necrotizing skin and soft tissue infection.

57.3 An otherwise healthy young man presents with a 5 cm abscess on the lateral buttock. He is afebrile. The correct management includes all of the following except:

A. Pack the abscess and have the patient remove the packing himself within 24 hours and soak or bathe twice per day.

B. Treat with an oral first generation cephalosporin.

C. Incise with a scalpel and explore and open the cavity with a clamp.

D. Provide analgesia with oral ibuprofen and a ring of local anesthetic around the abscess.

57.4 Which of the following is true about necrotizing soft tissue infections?

A. Blood pressure in the normal range and normal renal function are strong evidence against this diagnosis.

B. In suspected cases, admission to a medical service for IV antibiotics with surgical consultation as needed is reasonable management.

C. Skin bullae or necrosis or subcutaneous crepitus or tissue gas on x-ray are usually found.

D. Poorly controlled diabetes is the most common risk factor in community onset infection.

E. Vancomycin to cover MRSA is recommended component of empirical antibiotics.

ANSWERS

57.1 A. Necrotic spider bites are unusual, whereas spontaneous furuncles (superficial skin abscesses) are extremely common in emergency practice. Patients with furuncles often complain of a “spider bite”. MRSA accounts for 50% to 60% of all SSTIs in US emergency departments and may be even more common in spontaneous furuncles. While most of these simple infections are cured by incision and drainage alone, if antibiotics are deemed necessary, MRSA coverage is a must, with either trimethoprim-sulfamethoxazole, doxycycline or clindamycin.

57.2 C. This case is a classical presentation for a deep buttock or thigh abscess related to heroin injection. A septic hip or necrotizing infection should also be considered, although consultation for suspected NSTI is premature at this point. Nonpurulent cellulitis is very unlikely and simply treating with antibiotics is incorrect management. These abscesses can be very large and may cause a low-grade fever. When there is no obvious fluctuance, imaging with should be pursued with ultrasound, or occasionally CT, to confirm the diagnosis and guide drainage. Needle aspiration is reserved for small facial abscesses, and has no proven diagnostic role. Given the fever, this patient will likely require IV antibiotics and admission, as well procedural sedation via IV.

57.3 B. In a healthy host, an abscess 5 cm or less with only minimal to moderate surrounding cellulitis does not require antibiotics. This is supported by multiple studies. Long acting local anesthetic, such as bupivicaine, should be deposited in a ring around the abscess several minutes before incision and drainage. Packing is advised for abscesses that are more than a cm or so below the skin surface, as is commonly encountered in the buttocks, but it can be removed by the patient, with or without repacking. Soaking and scrubbing with soapy water is also recommended.

57.4 E. Necrotizing soft tissue infections are uncommon but potentially devastating and the diagnosis is rarely obvious at first presentation. Shock or organ dysfunction is initially evident in only 0% to 40% of cases. Classical skin signs are important red flags to recognize, but are frequently absent, and gas on plane x-ray is seen in 30% of cases, at most. Risk factors include diabetic foot ulcer, infections of the scrotum and perineum in men and injection drug use–which, in urban centers, is the leading cause of community onset necrotizing infections. Importantly, group A streptococcal NSTIs can occur spontaneously. NSTIs caused by community-associated MRSA have been reported.

REFERENCES

Chen JL, Fullerton KE, Flynn NM. Necrotizing fasciitis associated with injection drug use. Clin Infect Dis. 2001;33(1):6-15. 

Jeng A, Beheshti M, Li J, et al. The role of beta-hemolytic streptococci in causing diffuse, nonculturable cellulitis: a prospective investigation. Medicine (Baltimore). 2010;89(4):217-226. 

Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S aureus infections among patients in the emergency department. N Engl J Med. 2006 17;355(7):666-674. 

Napolitano LM. Severe soft tissue infections. Infect Dis Clin North Am. 2009;23(3):571-591. 

Talan DA. Lack of antibiotic efficacy for simple abscesses: have matters come to a head? Ann Emerg Med. 2010;55(5):412-414.

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