In the OR, the surgeon made a 3.0-cm incision, conducted an exploration, and identified a cavity that contained a small amount of purulence. He determined the lesion to be a resolving abscess. The wound was washed out, and the area was closed with a Penrose drain.
The patient was continued on the piperacillin/tazobactam. His blood culture was positive for gram-positive rods, and a low-grade fever persisted. An infectious disease specialist was consulted, and levofloxacin was added to the patient’s regimen.
After 24 hours of treatment, findings on urinalysis improved: blood, small; protein, trace; nitrites, negative; leukocytes, small; WBCs, 15 to 20/high-power field; and no bacteria. Over the next three days, the patient’s condition continued to improve. His hand drain was removed, and the pain and swelling subsided. He became afebrile, and his WBC count fell to 24,700/mcL. He was discharged to home with prescriptions for cephalexin and levofloxacin. Follow-up for postoperative care was arranged with the hand surgeon.
Discussion
Pyomyositis is defined as abscess formation deep within large striated muscles.1 Although this condition is uncommon, it is believed that an occult bacteremia can seed an area of damaged muscle (compared with healthy muscle, which ordinarily resists infection), allowing an abscess to form.1,2
Epidemiology
In a 2002 review involving 676 patients with primary pyomyositis, Bickels et al3 reported the condition in ages ranging from two months to 82 years (mean, 28.1 years). In a majority of cases, only a single muscle was involved; 112 patients (16.6%) were identified with multiple-site involvement. Only seven cases (0.1%) involved the hand.
In 452 cases (66.9%), a bacterial agent was identified. Among these, 350 (77%) had a positive culture for Staphylococcus aureus. Other isolates included Streptococcus pyogenes, Escherichia coli, Salmonella enteritidus, and Mycobacterium tuberculosis.1,3 It should be noted that community-acquired methicillin-resistant S aureus (CA-MRSA) is being implicated with increasing frequency in cases of pyomyositis.4-6
Because pyomyositis is not a reportable disease and has not been studied in large clinical trials, its incidence is uncertain, and proposed risk factors have not all been confirmed2 (see Table2,7).
Pathophysiology
While the etiology of primary pyomyositis is unclear, it is believed to be caused by a combination of bacteremia (chronic or transient) and damaged muscle. In a 1960 study published in the Lancet, Smith and Vickers8 performed autopsies on 327 patients who had died of culture-positive septicemia. Only two patients were found to have a muscle abscess. At that time, the investigators concluded that both muscle injury and bacteremia would need to be present in order for an abscess to form. In animal studies, bacteremia (eg, S aureus) does not appear to lead to pyomyositis except in cases of muscle abnormality or trauma (eg, electric shock, pinching injury).9,10
When a history of trauma can be identified in patients with pyomyositis, the condition typically develops near the affected muscle, and the infection appears within days to weeks.3 In cases in which an antecedent infection is identified and hematogenous spread of the bacteria to the skeletal muscle occurs, this is termed secondary pyomyositis.11
Disease Progression
Pyomyositis generally progresses in three stages, beginning with inflammation and advancing to a focal abscess, then to a septic state.3 The first stage develops between seven and 21 days after the initial incident, is typically subacute, involves mild pain and swelling with a “woody” texture, and is occasionally associated with fevers.2
Diagnosis of pyomyositis is usually made during the second stage, 10 to 21 days after the initial incident; by that time, the pain has increased, and the fever is more pronounced. Third-stage infection usually involves fluctuance and sepsis.2
Although MRI is considered most useful in the diagnosis of pyomyositis, CT and ultrasound allow for percutaneous needle aspiration and drainage.3
Treatment
The correct treatment for pyomyositis depends upon the stage at which the disease is identified. During the first stage (before formation of an abscess), antibiotic treatment alone may be sufficient.1 Once an abscess has formed, an incision and drainage will be required, in conjunction with or followed by appropriate antibiotic therapy.
When pyomyositis is properly treated during the first or second stage, a full recovery is likely.2,3 By the third stage, surgical debridement is required. Additionally, osteomyelitis may develop in the adjacent bones, followed by muscle scarring, residual weakness, and functional impairment.2,3 Reported pyomyositis-associated mortality ranges between less than 1% and 4%.2,12
The Case Patient
The case presented here was of particular interest for two reasons. First, the patient had a traumatic injury that initially caused him no concern but worsened progressively over 14 days. Although this is not the typical presentation of a traumatic injury, the ED staff could very easily have performed a radiograph, made a diagnosis of traumatic hand injury, and discharged the patient.