beyond the area of vascular gangrene to involve viable muscle.Proteusspp.,Bacteroidesspp.,
and anaerobic streptococci are among the bacteria found in such lesions (11,62).
PYOMYOSITIS
Pyomyositis is an infection of the skeletal muscle predominantly caused byS. aureusand
Streptococcusspp. (63,64). Other rare organisms include Enterobacteriaceae and anaerobic
bacteria. Case reports ofAspergillus fumigatus,Cr. neoformans,M. tuberculosis, andM. avium-
intracellularehave been reported (65,66). It was originally recognized in patients who acquired
the disease in the tropics. Predisposing condition includes diabetes mellitus, cirrhosis,
immunosuppressive illness, and HIV, and has been reported in IV drug abusers. Presumed
pathogenesis involves a prior bacteremia, commonly transient. Bacterial infection of the
muscle usually occurs after a penetrating wound, vascular insufficiency, or a contiguous
spread. Common muscle involvement includes deltoid, psoas, biceps, gastrocnemius, gluteal,
and quadriceps, though any muscle group can be involved. Patients will typically present with
fever, pain, tenderness, and swelling of the involved muscle. Bacteremia is present in 5% to
35% of cases. The diagnosis is best established by computed tomography scan or MRI.
Treatment consists of drainage (percutaneous or open incision). Initial antibiotics today
should consist of IV administration of vancomycin, linezolid, or daptomycin since MRSA
should be suspected. Early modification of initial antimicrobial therapy is based on Gram stain
and culture results.
DIABETIC FOOT INFECTION
Defined as any inframalleolar infection in a person with diabetes mellitus. These include
paronychia, cellulitis, myositis, abscesses, NF, septic arthritis, tendonitis, and osteomyelitis.
The most common lesion requiring hospitalization is the infected diabetic foot ulcer (Fig. 7).
Neuropathy plays a central role, with disturbances of sensory, motor, and autonomic functions
leading to ulcerations due to trauma or excessive pressure on a deformed foot. This wound
may progress to become actively infected, and by contiguous extension the infection can
involve deeper tissues. This sequence can be rapid, especially in an ischemic limb. Various
immunological disturbances, especially involving the polymorphonuclear leukocytes, may
affect some diabetic patients.S. aureusand theb-hemolytic streptococci (groups A, C, G,
especially group B) are the most commonly isolated pathogens. Chronic wounds develop a
more complex colonizing flora including enterococci; Enterobacteriaceae; obligate anaerobes,
P. aeruginosa; and other nonfermentative gram-negative rods (67–69). Hospitalization, surgical
procedures, and prolonged antibiotics predispose patients to colonization and infection with
MRSA or vancomycin-resistantEnterococcus(VRE). Community-acquired cases of MRSA are
becoming more common. Finally, there have been at least two reported cases of vancomycin-
resistantS. aureus(VRSA) involved a diabetic patient with a foot infection (70).
Therapy
Initial therapy is empirical and should be based on severity of infection and available
microbiological data, such as recent culture results or current smear findings from adequately
obtained specimens. The microbiology can be identified by culture only if specimens are
collected and processed properly. Deep tissue specimens, obtained aseptically at surgery,
contain the true pathogens more often than do samples obtained from superficial lesions. A
curettage or tissue scraping with a scalpel from the base of a debrided ulcer provides more
accurate results. An antibiotic regimen should always include an agent active against
staphylococci and streptococci. Previously treated or severe cases may need extended coverage
that also includes commonly isolated gram-negative bacilli andEnterococcusspp. Necrotic,
gangrenous, deep, or foul smelling wounds usually require antianaerobic therapy. For
moderate to severe infection ampicillin/sulbactam or piperacillin/tazobactam can be used. For
life-threatening infections imipenem/cilastin may be a consideration. A high prevalence of
MRSA may require use of vancomycin or other appropriate agents against these organisms.
The duration of treatment for life-threatening infection may be two weeks or longer. Many
infections require surgical procedures that range from drainage and excision of infected and
necrotic tissues to revascularization or amputation (for treatment refer to Table 3).
308 Sharma and Saravolatz