Pyomyositis of the iliacus muscle in an adolescent.

To the Editor: A ten-year-old female presented to the Emergency Room with the acute onset of left hip pain and was non-ambulatory when she was admitted to the hospital. On initial examination, she was in severe pain. She was afebrile with stable vital signs. The hip appeared normal, with no erythema or swelling, although it was very tender to palpation. She denied pain in other regions. The remainder of her physical exam and her past medical history were non-contributory. Initial laboratory findings showed a normal complete blood count with differential (CBCD), complete metabolic panel (CMP), and erythrocyte sedimentation rate (ESR). Plain films of her hip, femur and pelvis were negative, as was an ultrasound of her left hip.

Shortly after admission, she became febrile. The next day a MRI was positive for an extremely enlarged left iliacus muscle (Fig. 1), consistent with the diagnosis of pyomyositis. During her stay, her white blood cell count increased to 14.2 and her ESR rose to 90. A repeat MRI on admission day 4 (Fig. 2) showed an abscess forming in her left iliacus. The abscess was drained by CT-guided aspiration, which grew Staphylococcus aureus. She was discharged after completing a course of IV antibiotics and was pain-free with normal mobility at her two week follow-up visit.

Pyomyositis is defined as a subacute, deep bacterial infection of skeletal muscle. Most frequently seen in areas of Africa and the South Pacific, it has been increasingly recognized with the common usage of MRI technology. (1)

Primary pyomyositis is most common in the pediatric population, with the large pelvic muscle usually affected. In a review of the literature of 676 patients, over half the cases were localized to the quadriceps, iliopsoas, and buttock regions. (2) S aureus is the most common pathogen isolated, with the bacteria accounting for greater than 75% of cases.

Pyomyositis usually follows a three-stage clinical course, beginning with a subacute stage, where the inflammation is localized to the muscle tissue. Symptoms at this time are nonspecific with only a low-grade fever and muscle aches present on examination. The second stage is formation of the muscle abscess with association of local and systemic findings. The diagnosis is most often confirmed at this stage, with the involved muscle increasingly swollen and tender. If not adequately treated, the third stage is reached, which include signs of toxicity and septic shock. One study in Nigeria reported 13% of the deaths in an emergency room were due to pyomyositis, where the incidence can be as high as 1:1,000. (3)

The length of time between the stages is highly variable. Our patient appeared at the very end of stage one, afebrile with normal laboratory findings. Routine laboratory evaluation is rarely helpful in confirming the diagnosis of pyomyositis and blood cultures are frequently negative.

The treatment of pyomyositis depends on its stage when the diagnosis is made. It always involves the early use of antibiotics, which if instituted before abscess formation, can serve as sole therapy. (4) However, once stage two has occurred, abscess drainage is required. Drainage is commonly performed by the use of percutaneous CT guidance. In most patients, a complete recovery is expected.

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Primary pyomyositis is an infrequent condition in pediatrics that is becoming more commonly recognized. Since it most often involves the large pelvic muscles, a careful history and physical, early antibiotic selection, and MRI utilization is essential to confirm the diagnosis. A high index of suspicion of pyomyositis is essential, and it should be considered in the differential diagnosis of acute onset of musculoskeletal pain. (5)

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David Zlotkin, MD

Texas Tech Health Science Center

Lubbock, TX

References

1. Gibson RK, Rosenthal SJ, Lukert BP. Pyomyositis, increasing recognition in temperate climates. Amer J Med 1984;77:768-772.

2. Bickles J, Ben-Sira L, Kessler A. Current Concepts Review: Primary Pyomyositis. J Bone Joint Surg (Am) 2002;84A:2277-2286.

3. Adesunkanmi AR, Akinkuolie AA, Badru OS. A five year analysis of death in accident and emergency room of a semi-urban hospital. West Afr J Med 2002;21:99-104.

4. Peckett W, Butler-Manuel A, Apthorp A Pyomyositis of the iliacus muscle in a child. J Bone Joint Surg Br 2001;83B:103-105.

5. Waagner DC. Musculoskeletal infections. In Adolescents. Adolescent Medicine: State of the Art Reviews; 11 (2), June 2000.