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Pyomyositis in a 5-Year-Old Child
Sam Romeo, MD;
Sam Sunshine, MD
Arch Fam Med. 2000;9:653-656.
ABSTRACT
We present a case of pyomyositis in an otherwise healthy 5-year-old child that underscores the potential for serious, life-threatening complications. Pyomyositis of the gluteal, psoas, and iliacus muscles was associated with osteomyelitis, septic arthritis, a large inferior vena cava thrombus, septic pulmonary emboli, and eventual pneumonia. Primary pyomyositis is a purulent infection of striated muscle thought to be caused by seeding from a transient bacteremia. The focal infection typically forms an abscess that generally responds to intravenous antibiotics and occasionally requires adjunctive computed tomography–guided aspiration and drainage. This localized infectious process rarely produces further sequelae unless treatment is delayed. Pyomyositis is rare in healthy individuals and requires a high clinical suspicion in patients who present with fever, leukocytosis, and localized pain.
INTRODUCTION
Pyomyositis is an uncommon infectious process that involves striated muscles. The etiology of pyomyositis is frequently classified as primary or secondary. The exact nature of primary pyomyositis remains unclear but is believed to be the result of hematogenous spread of an occult source. Secondary pyomyositis is usually a consequence of direct extension from an infectious process, most notably Crohn disease, infectious colitis, appendicitis, and neoplasm. Secondary pyomyositis, although not further discussed herein, may also result from penetrating trauma, even without a foreign body left behind. Treatment of primary pyomyositis involves intravenous antibiotics with the use of percutaneous computed tomography (CT)–guided aspiration or open surgical drainage as needed for abscess drainage. The complication rate of pyomyositis is rare, unless the treatment is delayed or inadequate, with overall published mortality rates of primary pyomyositis ranging from 2% to 10%.1-3 As presented herein, even with early intervention, antibiotic therapy, and drainage, pyomyositis can still result in life-threatening complications such as septic pulmonary emboli and pneumonia, presumably seeded from a large inferior vena cava thrombus neighboring the infected muscles. Furthermore, although often considered in the differential diagnosis of primary pyomyositis, little has been described about the concurrent involvement of a septic joint and osteomyelitis.
REPORT OF A CASE
A 5-year-old African American boy presented with a chief complaint of right hip pain for 4 days prior to admission. He fell off his bicycle, and the following day reported right hip pain. The patient's mother noticed a progressively worsening limp, which prompted the office visit. He also experienced concomitant fevers that started 1 day after his fall, which had been treated with ibuprofen.
On physical examination, the patient appeared well nourished but in moderate pain. His temperature was 39.5°C; pulse, 107/min; respiratory rate, 24/min; and blood pressure, 91/55 mm Hg. His right hip was held in a flexed position. Both his hip and knee were tender to palpation without significant increase in warmth to either area. He demonstrated an antalgic gait and reported severe pain with motion of his ipsilateral hip and knee.
Significant diagnostic data were as follows: white blood cell count, 20.8x109/L; 0.34 neutrophils, 0.32 bands, and 0.30 lymphocytes; and erythrocyte sedimentation rate, 120 mm/h. A CT scan of the pelvis was obtained to further evaluate a suspected septic right hip joint following inconclusive plain radiographs of the hip and knee. The CT images through the pelvis demonstrated the following: (1) a large discrete abscess in the iliacus muscle with a fluid collection within the right iliac fossa and swelling of the ipsilateral psoas muscle (Figure 1); (2) a second discrete large septated fluid collection within the right gluteus medius muscle (Figure 2); (3) a large thrombus within the inferior vena cava and both common iliac arteries (Figure 3); and (4) no presence of fluid within the hip.
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Figure 1. Iliacus muscle abscess.
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Figure 2. Gluteus medius abscess.
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Figure 3. Thrombosed inferior vena cava.
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The purulent fluid collections within the iliacus and gluteus medius muscles were drained under CT guidance, and a single drainage catheter was placed into each infectious site and connected to a Jackson-Pratt bulb for suction. On the day of presentation, a CT-guided hip aspiration of the right hip joint was carefully performed without passing the needle through an infected site to rule out a septic hip (Figure 4). There was no spontaneous efflux of fluid with aspiration of the hip and no evidence of pus in the joint, so the joint was flushed with isotonic sodium chloride solution and the aspirate was sent for Gram staining and cultures. Owing to the above findings, an orthopedic consult was made, which determined that the hip did not need to be surgically opened and drained as would have been necessary if the joint was found to have a large effusion or purulent aspirate. Intravenous heparin sodium and triple antibiotic therapy with nafcillin sodium, gentamicin sulfate, and metronidazole hydrochloride was initiated. Cultures of the aspirated abscesses, right hip, and sputum yielded Staphylococcus aureus. Gram stain results of the hip showed 2+ white blood cells and 4+ Gram-positive cocci in pairs and clusters. During the subsequent 2 weeks, follow-up CT scans of the chest, abdomen, and pelvis demonstrated resolving abscesses and progressive diminution of the inferior vena cava thrombus. The patient, however, developed pneumonia in the right lower lobe and was found to have septic emboli, presumably from the inferior vena cava thrombus (Figure 5). A ventilation-perfusion ( - ) scan confirmed perfusion defects. Intermittent fevers continued for 13 consecutive days despite appropriate antibiotic coverage based on culture sensitivities. Because of the patient's poor initial response, the antibiotic regimen was switched to vancomycin, tobramycin, and metronidazole hydrochloride. The patient defervesced 3 days later and remained afebrile for the last 5 days of hospitalization. The final CT scan demonstrated erosion of the right ileum; the presence of osteomyelitis was confirmed with a gallium scan. Nearly 3 weeks after admission, the patient was ambulating without pain and was discharged on a regimen of intravenous nafcillin for an additional 3 weeks. Oral warfarin sodium therapy was started after the patient was found to have a thrombosed inferior vena cava and continued until a negative - lung scan was demonstrated, nearly 8 months later.
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Figure 4. Computed tomography–guided aspiration of the right hip.
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Figure 5. Cannon ball lesions. Cavitary septic emboli in the lungs characteristic of Staphylococcus infection.
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COMMENT
Primary pyomyositis is an uncommon infectious process that involves skeletal muscle. The classical history consists of 3 clinical phases that correlate with the progression from the early seeding of bacteria into muscle, to localized suppuration, and ultimately to significant systemic signs including shock if left untreated. Initially characterized by a dull, insidious ache, the affected area usually gets progressively erythematous and swollen. A subjective increase in focal symptoms with systemic signs including leukocytosis and fever typifies the most common patient presentation and represents the suppurative phase. Tropical pyomyositis will include eosinophilia at this stage but this is much less common in developed countries. This report mainly focuses on nontropical primary pyomyositis because the pathophysiologic features, clinical course, and response to treatment is similar for both. If left untreated, pyomyositis can progress to a late phase consisting of septic shock and even death.
Although the exact cause of primary pyomyositis remains unclear, several studies have demonstrated an association with muscular trauma. The frequently sited study by Miyake4 in 1904 demonstrated that dog muscles traumatized by pinching, electric shock, or ischemia would subsequently develop muscle abscesses when exposed to intravenous injections of S aureus, but nontraumatized tissue would not. From this study, one could surmise that traumatized tissue appears to be more susceptible to infection in the setting of bacteremia while nontraumatized skeletal muscle is relatively resistant to infectious seeding. Bresee and Edwards5 reported the association of trauma to subsequent development of pyomyositis when they found that 36% of 104 pediatric patients with psoas abscesses had a history of trauma. In 1992, other investigators reported similar results when they studied 98 patients aged 6 weeks to 79 years and found that 39% of cases of pyomyositis were associated with recent trauma.6 Similar studies of the relationship between trauma and subsequent development of osteomyelitis have also shown an increase in bone susceptibility after tissue damage.7 These results likely explain the concurrent development of both pyomyositis and osteomyelitis in the present case in which several noncontiguous structures such as the right gluteus medius muscle and the right iliacus muscle were involved after blunt trauma to the right hip. Multiple discrete foci of infections are consistent with bacterial seeding rather than direct extension; presumably, trauma with subsequent hematoma formation provides a fertile setting for the infectious process.
Primary pyomyositis has no universal cause, but suggested etiologic factors include trauma in the setting of bacteremia, parasites, and tropical climate. Other common factors that have been associated with an increased risk of pyomyositis include, but are certainly not limited to, the following: (1) the immunosuppression accompanying the acquired immunodeficiency syndrome, malignancy, type 1 diabetes mellitus, immunosuppressive therapy, neutropenia, renal failure, and malnutrition8; (2) muscle breakdown or inflammation after vigorous exercise9; and (3) concurrent infections such as osteomyelitis.
When evaluating a suspected case of pyomyositis, the differential diagnosis is wide and includes deep venous thrombosis, osteomyelitis, septic arthritis, hematoma, cellulitis, appendicitis, and sarcoma. Laboratory tests are nonspecific but usually reveal a moderate leukocytosis with a left shift, an elevated erythrocyte sedimentation rate frequently higher than 100 mm/h, and no elevation in muscle enzyme levels. Blood cultures are positive in 31% of all North American cases.6 The predominant organism isolated from purulent material obtained by needle aspiration or surgical drainage is S aureus, which is found in approximately 70% of North American cases but may be as high as 90% of pediatric cases.1, 6
Because of the lack of specificity of laboratory testing, high clinical suspicion and early radiologic evaluation are key to diagnosis. Appropriate imaging studies may include magnetic resonance imaging (MRI), CT, gallium scanning, bone scanning, or ultrasonography. Magnetic resonance imaging is the most sensitive test and provides a detailed look at soft tissue. Abscess formation, fluid collections, mass effects from inflammation, and concurrent involvement of bone and/or joint as seen in this case report can all be detected. Spiegel et al10 also suggested that MRI with gadolinium enhancement, if ordered early enough in the disease process, could be used to differentiate between the preabscess invasive stage and the suppurative stage that frequently requires drainage. As noted, this distinction may avoid unwarranted surgical involvement and identify patients needing only intravenous antibiotics. A potential problem with using MRI in diagnosis is its exquisite sensitivity to inflammatory changes. In the study by Spiegel et al,10 MRI revealed pathologic changes of osseus and articular stuctures in 7 of 12 cases. Although one could only speculate whether the patients truly had osteomyelitis or reactive inflammatory changes, MRI findings should be reviewed cautiously as to avoid overtreating. There were no reported treatment failures or recurrences in patients with abnormal MRI findings who received shorter antibiotic courses ranging from 2 to 6 weeks.10
Computed tomography is commonly used to identify fluid collections, abscess formation, and extensive muscle inflammation, and to guide in percutaneous drainage. Typically, the CT scan shows inflammation as enlargement of the involved muscles with or without abscess formation or fluid collection. As demonstrated in this case report, the CT scan may also reveal concurrent osseus involvement or a deep venous thrombosis adjacent to the inflamed area. Deep vein thromboses can also be detected using a Doppler study. However, this method in the setting of pyomyositis has been associated with false-positive results because blood flow may be decreased due to extravascular compression from an abscess or surrounding inflammation rather than actual intravascular thrombosis.6, 11 In the suppurative phase, nuclear scans may also be useful in the diagnosis of primary pyomyositis. Nuclear scans have the added benefit of identifying multiple sites of involvement owing to the diffuse distribution of nuclear markers.
Treatment of pyomyositis involves appropriate antibiotic coverage. Drainage is indicated when an abscess is present. The duration of treatment has not been well established, and has varied from 1 to 6 weeks based on clinical severity.
Empiric coverage should be broad in scope but must include S aureus coverage as it is the most common pathogen associated with pyomyositis. Therapy can be tailored after culture and sensitivity results are obtained. As was successfully performed in the patient of this case report, percutaneous CT-guided drainage may be as efficacious as open surgical drainage and is rapidly becoming the therapeutic intervention of choice.10, 12-14
AUTHOR INFORMATION
Accepted for publication March 23, 2000.
Corresponding author: Sam Romeo, MD, Department of Family Practice, Kaiser Permanente, 9961 Sierra Ave, Fontana, CA 92335.
From the Department of Family Practice, Kaiser Permanente, Fontana, Calif.
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