Infections of the extremities
Infections of the extremities range from common minor problems to unusual life-threatening disorders. Most patients have no serious underlying medical problem, but the possibility of undiagnosed disorders such as diabetes, immunodeficiency and vascular insufficiency must be considered.
Cellulitis is a common infection of skin and subcutaneous tissues, most frequently caused by Streptococcus pyogenes and occasionally Staphylococcus species. Infection occurs after the skin is breached (e.g. insect bite, scratching, skin rash, minor trauma). Cellulitis may seem to occur spontaneously, although careful inspection reveals a break in the skin. Lower limb cellulitis is associated commonly with broken skin between the toes due to tinea pedis. Cellulitis may complicate preexisting limb oedema. After subcutaneous inoculation, streptococci release toxins which permit rapid spread of organisms. The acute inflammatory response results in the clinical features of warmth, pain and tenderness, erythema, and oedema. Severe cellulitis may progress to suppuration and skin necrosis.
Differential diagnosis includes other causes of limb swelling, deep venous thrombosis, rupture of a Baker's cyst, calf haematoma and erythematous skin conditions.
Cellulitis of an extremity is treated by elevation and immobilisation with a splint or plaster ‘back slab’, and antibiotics. Penicillin (2 million units every 6 hours) or flucloxacillin (1–2 g every 6 hours) is given intravenously for 3–5 days and then continued orally for a further 10 days. Blood levels of penicillin may be increased by oral probenecid, which reduces renal excretion of penicillin. Erythromycin or a thirdgeneration cephalosporin is used in patients with penicillin allergy. Any predisposing cause (e.g. tinea pedis) is treated vigorously. If cellulitis does not resolve rapidly, the antibiotic is increased or changed, a deep collection of pus is sort, and the diagnosis is reviewed.
Lymphangitis is associated with bacterial infections of extremities where the inflamed lymphatic vessels appear as several thin, red, tender lines on the slightly oedematous skin progressing towards the regional lymph nodes which are enlarged and tender (lymphadenitis). Lymphangitis usually is caused by streptococci and staphylococci. Chemical lymphangitis may result from irritative compounds used for lymphangiography.
Treatment is the same as for cellulitis, consisting of rest and elevation of the extremity and antibiotics. Rarely, suppurative regional lymph nodes require surgical drainage.
Folliculitis, furuncles and carbuncles
‘Folliculitis’ refers to infection with pus formation within a hair follicle and is limited to the dermis. It may be extensive if many follicles are infected over a wide area, such as the face.
A ‘furuncle’ is infection of a small number of hair follicles within a small confined area. A ‘carbuncle’ is an abscess involving a number of adjacent hair follicles where the infection has penetrated through the dermis and formed a multiloculated subcutaneous abscess between the fibrous septa which anchor the skin to the deep fascia. Furuncles and carbuncles occur most frequently on the back of the neck, lower scalp, and the torso. Abscesses on the upper part of the body are usually caused by staphylococci, while infections below the umbilicus are due largely to aerobic and anaerobic coliform organisms.
Local hygiene is usually sufficient to treat folliculitis, although antibiotics are required for extensive infections. Furuncles and carbuncles require incision and drainage. Fibrous tissue septa must be broken down so that all pockets of pus can be drained completely. Antibiotics are indicated for severe and spreading infections, and in immunocompromised patients.
Hidradenitis suppurativa refers to infection of apocrine sweat glands, and occurs in the axillae, around the external genitalia, and the inguinal and perianal regions (see Anal and perianal disorders). Apocrine sweat glands have tortuous secretory ducts within the skin and produce thick secretions, and infection occurs when ducts become blocked, most commonly during excessive glandular activity at adolescence. Staphylococci or Gramnegative bacilli and anaerobes are causative organisms.
Patients present with multiple small but painful abscesses and sinuses, often bilaterally. Repeated or long-standing infection results in considerable scarring, which hinders resolution. Antibiotic therapy alone is often inadequate, although long-term antibiotic therapy may be useful in suppressing acute infections. Abscesses require incision and drainage. Excision of the affected hair-bearing area and the subcutaneous fat usually is required, and results in good symptomatic relief.
Acute paronychia (Whitlow) is a subcuticular abscess of the nail fold. Infections, usually due to staphylococci, follow minor injury to the nail fold, and begin as cellulitis. Pus forms around the nail fold (Transverse section of acute paronychia with subungual extension.) and may extend around the whole periphery of the nail, causing pain and inflammation extending proximally from the nail fold towards the distal interphalangeal joint.
Treatment consists of flucloxacillin and, if pus is present, drainage under digital local anaesthetic block using lignocaine without adrenaline and a finger tourniquet. The nail fold is lifted away from the nail to expose the edge of the nail which is excised to allow the pus to drain.
Chronic paronychia is a fungal infection of the nail fold. The nail becomes loose and deformed, and ridged or pock-marked. The nail fold is grossly thickened, and the cuticle is absent. Treatment consists of removal of the nail and long-term oral treatment with antifungal medication (e.g. griseofulvin). A subungual amelanotic melanoma may be misdiagnosed as chronic paronychia.
Pulp space abscess
A pulp space abscess (Felon) is a subcutaneous abscess of the pulp overlying the terminal phalanx (Longitudinal section of the finger tip with a pulp space abscess.). It follows a minor penetrating injury (e.g. thorn or pin prick), and starts as cellulitis and develops as subcutaneous pus forms. The overlying skin changes from red to a mauve-blue colour, implying imminent necrosis. Sloughing of pulp tissue, lymphangitis, acute suppurative tenosynovitis, and osteomyelitis are potential complications.
Treatment requires antibiotics and drainage of pus. When the abscess is small, an incision is made along the side of the pulp and deepened into the pulp space, breaking down the fibrous septa between the distal phalanx and the skin to ensure complete drainage. When the abscess is pointing to the centre of the pulp, the incision is made over it.
Pyomyositis is a purulent infection of skeletal muscle. The infection may complicate a penetrating injury (e.g. needle puncture), blunt trauma close to an infective skin lesion, or a spontaneous bleed into muscle (e.g. in an anticoagulated patient). Severe local pain, fever and inability to move the extremity are characteristic. Pyomyositis requires intensive antibiotic treatment, and aspiration or surgical drainage of pus.
‘Synergistic gangrene’ refers to a group of soft tissue infections (not necessarily restricted to the extremities) characterised by tissue necrosis and caused by several species of microorganisms acting synergistically. Previous nomenclature (necrotising fasciitis, necrotising erysipelas, Meleney's gangrene, Fournier's gangrene, non-clostridial gangrenous cellulitis) was confusing and attempted to associate a characteristic clinical syndrome with a bacteriological diagnosis.
Synergistic gangrene is caused by micro-aerophilic streptococci acting synergistically with aerobic staphylococci, with or without Gram-negative bacilli. It usually occurs in debilitated patients with other disorders (e.g. diabetes, malnutrition, alcoholism, liver disease, renal failure, malignant disease, immune compromise).
Synergistic gangrene presents initially as cellulitis with severe pain which is out of keeping with the minor local clinical signs but consistent with the seriousness of the condition. Infection spreads rapidly along fascial and subcutaneous planes without a severe inflammatory reaction. Bacterial toxins cause tissue and skin necrosis. Crepitus occurs when gas-forming organisms are present. Signs of systemic sepsis and toxaemia occur quickly.
‘Fournier's gangrene’ is the name given to synergistic gangrene involving the perineum and scrotum. It may be extensive and involve the abdominal wall and buttocks, and is a rare complication of anorectal and perineal surgery, trauma or minor infection.
Synergistic gangrene must be treated urgently by debridement of necrotic tissue, antibiotics and general supportive therapy (Treatment of synergistic gangrene).
Clostridial infections are unusual but serious. They include clostridial myonecrosis and cellulitis, and are not limited to the extremities. ‘Gas gangrene’ is a confusing term often used to describe infective gangrene with subcutaneous gas production by organisms that are assumed to be clostridial, but in fact most gas-producing infections are not clostridial. Strictly speaking, ‘gas gangrene’ refers to clostridial myonecrosis and cellulitis with gas formation.
Clostridia are anaerobic, spore-forming Grampositive bacilli found in soil, manure, marine sediment, decaying plants and animals, and the colon. When a wound is contaminated with clostridia, the likelihood of infection depends on:
- inoculum size
- virulence of the clostridial strain
- conditions within the wound being conducive to clostridial multiplication and tissue invasion (e.g. open fractures, deep wounds, haematoma, ischaemic or devitalised muscle and tissue, foreign bodies especially soil).
Clostridia produce potent exotoxins (haemolysin, collagenase, hyaluronidase, lecithinase and proteolytic enzymes) which cause tissue destruction and facilitate bacterial spread.
Clostridial infections are prevented by adequate initial treatment of contaminated wounds, antibiotics and passive immunisation (Prevention and treatment of clostridial infections). Treatment of established infection is by urgent surgical debridement of the wound, high-dose antibiotics, and supportive therapy with or without hyperbaric oxygen (Prevention and treatment of clostridial infections). Mortality is high (25–40%) and associated with delayed diagnosis and treatment, severity of septic shock, poor medical condition prior to infection, and failure to control infection at the first operation.
Clostridial myonecrosis is a rare, acute infection of muscle. In civilian hospital practice, it occurs in inadequately debrided traumatic wounds and in amputation stumps in diabetics and vasculopaths.
After inoculation, clostridia multiply and release exotoxins which disrupt tissues and increase capillary permeability, and produce profound systemic toxaemia. Infected muscle is initially inflamed, oedematous and friable, and rapidly becomes necrotic. Overlying skin has a marbled mauve appearance and later turns black. Gas may be present in the tissues. The wound discharges a thin, non-purulent fluid with a characteristic sickly sweet smell. The limb is severely painful, and septic shock, haemolysis and jaundice develop rapidly. The incubation period is 1–3 days, but once infection is established, the wound appearance and systemic toxaemia develop over a few hours.
The diagnosis of clostridial myonecrosis must not be delayed because mortality increases dramatically when treatment is not instituted urgently. Diagnosis is made on the clinical setting and appearance of the extremity, and confirmed by urgent microscopy of a wound swab, which reveals numerous Gram-positive bacilli and few leucocytes.
Clostridial cellulitis is an infection of subcutaneous or extraperitoneal tissues. It spreads rapidly along tissue planes, causes small vessel thrombosis and tissue necrosis, but does not involve underlying muscle. Subcutaneous gas may form. Wounds have a foul-smelling serosanguinous discharge. Pain, tissue swelling and systemic toxaemia are of moderate severity.
Williams JD, Taylor EW, eds. Infections in Surgical Practice. London: Arnold; 2003.
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