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Kunwardeep Sohal, PGY 3
 A purulent infection of skeletal muscle that arises
from hematogenous spread, usually with abscess
formation
 Classically an infection of the tropics, although it has
been recognized in temperate climates with increasing
frequency (most ly in adults, with males affected more
than females)
 Most patients with tropical pyomyositis are otherwise
healthy without underlying comorbidities, while most
patients in temperate regions are
immunocompromised or have other serious
underlying conditions
 Immunodeficiency: HIV, Diabetes, Malignancy,
Cirrhosis, Renal Insufficiency, Organ Transplantation
and Immunosuppressive agents
 HIV particularly important; the predisposition to
pyomyositis is unclear, but factors may include immune
compromise, primary HIV myopathy, antiretroviral
therapy, and increased rates of staphylococcal carriage
 In a review of 98 cases in North America, about half of
pyomyositis patients with underlying medical
conditions were seropositive for HIV (Clin Infect Dis
1992)
 Trauma: about 25-50% of patients with pyomyositis
report a history of trauma. In addition, pyomyositis
has been described in temperate regions among
athletes performing vigorous exercise, suggesting the
potential role of minor muscle damage in the
pathogenesis of the disease
 Postulation? Possibly related to hematoma formation,
followed by infection or increased perfusion due to
trauma (making this area a favorable environment for
bacteria with additional iron being provided)
 Injection drug use, and concurrent infection
(toxocariasis-cat or dog roundworm, varicella
infection)
 Staphylococcus aureus is the most common cause of
pyomyositis; it causes up to 90 percent of tropical
cases and up to 75 percent of temperate cases (with
MRSA and community acquired strains becoming the
most dominant)
 Group A streptococci is the second most common
pathogen
 Usually polymicrobial in diabetic patients
 Hallmark: fever and pain/cramping in single muscle
group
 Occurs most often in lower extremities (sites include
the thigh, calf and gluteal muscles)
 Multifocal infection with involvement of more than
one muscle group may be observed in up to 20 percent
of cases
 Stage 1: crampy local muscle pain, swelling, and low-grade
fever
 mild leukocytosis
 induration of affected muscle may be present; no fluctuation;
deep abscess may not be discretely palpable, but the muscle
may have a "woody" texture on palpation
 2% of patients present at this stage
 Stage 2: usually 10-21 days after onset of symptoms
 characterized by fever, exquisite muscle tenderness, and
edema
 frank abscess may be clinically apparent
 marked leukocytosis
 90% present at this stage
 Stage 3: systemic toxicity, affected muscle is fluctuant
 Complications of S. aureus bacteremia such as septic
shock, endocarditis, septic emboli, pneumonia, and ARF
may be present
 Course and presentation is variable with most
presenting in Stage 2, however can be indolent, a delay
in diagnosis in such cases may result in involvement of
multiple muscle groups, requiring prolonged therapy
 **Occurs as a result of bacteremia, must r/o
endocarditis!
 Muscle strain
 Contusion
 Hematoma
 Cellulitis
 DVT
 Osteomyelitis
 Septic arthritis
 Neoplasm
 Clostridial myonecrosis vs necrotizing fasciitis vs
spontaneous gangrenous myositis vs diabetic muscle
infarction vs septic arthritis and other forms of myositis
 Radiology, cultures and lab data
 Radiology: Computed tomography (CT) is helpful for
detecting muscle swelling and well-delineated areas of
fluid attenuation and rim enhancement with contrast (VIR
directed drainage); MRI picks up subtle differences in
terms of extent in muscle
 Cultures: positive in up to 10 percent of tropical cases and
35 percent of temperate cases
 Lab data: leukocytosis with shift, elevated inflammatory
markers (ESR, CRP), eosinophilia should raise suspicion for
a concomitant parasitic infection
 **Counterintuitively, CK levels are often normal
 Although stage 1 pyomyositis can be treated with
antibiotics alone, most patients present with stage 2 or
3 disease and therefore require both antibiotics and
drainage for definitive management
 Drainage: CT-guided percutaneous drainage is the
modality of choice when feasible
 However, in the setting of deep infection or extensive
muscle involvement with significant necrosis, surgical
intervention may be required
 Diagnostic drainage can also be performed initially to
direct antibiotic therapy
 Abx: For immunocompetent individuals, initial empiric
parenteral antibiotic therapy should be directed against
staphylococci and streptococci
 Empiric therapy for MRSA should be initiated for patients
with a previous episode of proven MRSA infection, patients
with risk factors for MRSA, and patients with systemic
toxicity
 In addition, it should be considered in communities where
the prevalence of MRSA is greater than 30 percent
 For immunocompromised individuals, vancomycin may be
combined with a broad spectrum regimen that has activity
against gram-negatives and anaerobes
 Duration: 3-4 weeks of parenteral therapy is usually
sufficient, although patients with extensive, multifocal
or poorly drained infection may warrant longer courses
of therapy (obviously longer if endocarditis or osteo
present)