Working Diagnosis:
Foot abscess

Treatment:
Initially treated for cellulitis with Ceftriaxone with no improvement. Vancomycin was added for broader antimicrobial coverage. Ultimately, this patient required surgical treatment.

Outcome:
Transferred to an institution with pediatric surgical specialists. The patient was taken to the operating room for incision and debridement twice. In the operating room, gray dishwater-colored fluid was drained from the foot.

Author's Comments:
Initially, it was thought that the patient had cellulitis causing the pain and swelling in the foot. The lack of improvement with antibiotics and the muscle findings on MRI seemed to indicate myositis, septic arthritis, fasciitis, or other infectious process. This patient had leukocytosis, elevated C reactive protein, and initially elevated creatine phosphokinase. The elevation in creatine phosphokinase signified that there was muscle involvement (1). Myositis has been known to cause focal pain, especially when it is following a viral infection. However, most commonly myositis presents as weakness (1). Each diagnosis on the differential list did not completely explain all labs and physical exam findings. Therefore, broad spectrum antibiotics and anti-inflammatory treatment was continued. MRI was the imaging modality initially chosen to reduce this pediatric patient’s exposure to radiation.​

The CT scan which revealed a fluid collection was unexpected. The patient had a negative MRI two days prior. MRI is often used to diagnose abscesses in the brain and spine, but capability in other areas of the body has not been established. The ability to identify abscess on CT vs MRI may be affected by the adjacent tissue types (3.) The fluid collection was drained, and cultures were overall negative except for two small colonies of candida parapsilosis, which may be a contaminate. Many other sterile abscesses have been found to be due to Mycobacterium tuberculosis (2.) However, acid fast bacilli smear and subsequent Mycobacterium culture did not reveal tuberculosis. ​

Perhaps it was pre-treatment with antibiotics that caused this abscess to be sterile. However, the question remains: how did a young, healthy female develop this with no known injury or penetrating trauma?

Editor's Comments:
Diagnosing superficial and deep musculoskeletal soft tissue infection can be challenging in clinical practice. Patients with limited or no risk factors may be particularly challenging cases. In fact healthy muscles are generally resistant to infection. Predisposing factors would include diabetes, drug use, malnutrition, immunodeficiency, malignancy or trauma. The majority of superficial infections can often be treated with aggressive medical management. However, deeper soft-tissue infections may require surgical intervention as in this case. It is critical to escalate treatment when clinically indicated to avoid delay in care. The use of advanced imaging can be particularly helpful. Nonetheless, it is imperative to be knowledgeable of the key imaging findings, possible patterns of soft-tissue involvement and appropriate use of imaging. The role of a multi-disciplinary approach in the care of this patient was key for a successful treatment strategy.

References:
Crum-Cianflone NF. Bacterial, fungal, parasitic, and viral myositis. Clin Microbiol Rev. 2008;21(3):473-494. doi:10.1128/CMR.00001-08

Malik Z, Shehab M. Mycobacterium tuberculosis pyomyositis in an infant. Ann Med Health Sci Res. 2013;3(2):282-284. doi:10.4103/2141-9248.113681

Wall SD, Fisher MR, Amparo EG, Hricak H, Higgins CB. Magnetic resonance imaging in the evaluation of abscesses. AJR Am J Roentgenol. 1985;144(6):1217-1221. doi:10.2214/ajr.144.6.1217

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