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The second set of biopsies were similar to the first with chronic inflammation and fibrosis in both the LUQ mass and the capsule of the liver. Fungal cultures, AFB stains, AFB cultures and TB PCR were negative. However, the Gram-stained smears revealed a few Gram-positive rods of varying lengths, some of which had a clearly beaded appearance. The culture grew pleomorphic, branching Gram-positive rods in broth only, which were initially identified as Propionibacterium acnes, but were later sent, along with tissue samples, to the Centers for Disease Control and Prevention (CDC) for evaluation, where the 16S rDNA analysis and specific PCR assays revealed the true identity of the organism as Aggregatibacter actinomycetemcomitans. The CDC’s interpretation of the tissue Gram stain is that the bacteria were thin Gram-positive rods. However, Aggregatibacter is a Gram-negative rod, which seems to contradict the findings on the patient’s tissue Gram stain. Bacterial Gram-staining patterns in tissue can be uncertain, as Gram-negative organisms can sometimes stain Gram positive. The patient was diagnosed with actinomycosis based on these combined CDC results.
A peripherally inserted central catheter was placed to allow for intravenous administration of ampicillin at home. After 4 weeks of intravenous ampicillin, he completed another 6 months of oral amoxicillin at home. He steadily gained weight, regained his baseline stamina and all of his lesions completely resolved on subsequent imaging studies. There was a possible irregularity of 1 rib adjacent to the left lower lobe mass seen on an early chest radiograph, but that was not confirmed nor seen again on any subsequent imaging studies, including computed tomographic and magnetic resonance imaging scans.
After his second biopsy, additional history was elicited, indicating that, approximately 9 months earlier, the patient had a near-drowning incident, when he accidentally fell from a dock into a deep-water lake. Not knowing how to swim, he became submerged and took in several gulps of water before being rescued by family members. It was soon thereafter that he began experiencing his first episodes of left flank pain. At a local hospital about 2–3 months later, a chest radiograph was not diagnostic and no treatment was offered.
Actinomycosis is a subacute or chronic bacterial infection that slowly produces a fibrotic inflammatory mass that can cavitate1 and drain sulfur-laden pus through sinuses.2 It can affect any part of the body, but the most common infections seen in children are in the cervicofacial, abdominopelvic, thoracic and central nervous system regions. A unique feature of actinomycosis is its tendency to cross fascial plains, usually spreading contiguously as opposed to hematogenous or via lymphatic routes.3 In the thoracic form, patients aspirate the bacteria and experience an insidious onset of cough and low-grade fever, which often progresses to weight loss and hemoptysis, and eventually to abscess formation with fibrosis.3 Consistent with these features, our patient’s thoracoabdominal fibrotic mass presumably started with his near-drowning episode, invaded the lung, crossed the diaphragm, extending into the retroperitoneal region.
Actinomycosis is caused by normal flora of the human oral cavity3,4 and, therefore, is not spread from person to person. The term actinomycosis describes an inflammatory syndrome caused by a variety of genera including Actinomyces, Propionibacterium, Bifidobacterium and Aggregatibacter.1 Infections are typically polymicrobial and are caused by a combination of several species6 of these low-virulence bacteria. It does not specifically require the presence of Actinomyces genera for diagnosis.1 Because this infection has more than a single cause, some sources have suggested using the term “actinomycoses.”1 As previously mentioned, A. actinomycetemcomitans, a Gram-negative fastidious coccobacillus which was isolated from our patient, is particularly common in pulmonary and cervicofascial disease.
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