Actinomycotic Cholecystitis and Pancreatitis: Report of an Unusual Case

Introduction

Actinomycosis is an uncommon bacterial infection caused by the commensal organism Actinomyces spp., which can become pathogenic upon tissue injury or mucosal barrier disruption, and whose clinical presentation varies depending on the affected site [1,2]. Cervicofacial actinomycosis often presents as a slowly progressive, painless mass that can evolve into abscesses and draining sinus tracts [3,4]. Abdominal actinomycosis, often triggered by recent surgery or trauma, can mimic Crohn disease or tuberculosis, presenting with abdominal pain, weight loss, and palpable masses [5,6]. Pulmonary actinomycosis can manifest with chronic cough, shortness of breath, and chest pain [7,8], while genitourinary involvement, often associated with intrauterine device use, can present with abdominal pain and vaginal discharge [9–11].

While primarily recognized for its cervicofacial and abdominopelvic presentations, actinomycosis can extend to the gallbladder and potentially the pancreas, posing diagnostic and therapeutic challenges due to its similarity to other conditions and the bacterium’s fastidious nature [12,13]. Cholecystitis and pancreatitis can occur as a consequence of Actinomyces spp. infection by either retrograde spread from the duodenum or hematogenous dissemination, often facilitated by the presence of gallstones or underlying mucosal injury [13–16]. Clinically, actinomycotic cholecystitis can mimic both acute and chronic cholecystitis, and even gallbladder carcinoma, further complicating diagnosis [17–19].

Here, we present the case of a 26-year-old woman with a history of recurrent acute pancreatitis and cholecystitis due to superimposed actinomycosis infection.

Case Report

The patient presented to our institution’s emergency department with a 1-day history of epigastric pain, a 3-day history of constipation, and flu-like symptoms, including hoarseness and cough. On examination, the patient appeared pale and dehydrated but was acyanotic, afebrile, and anicteric, with a normal heart rate and blood pressure. The abdomen was flaccid, flat, and tender to palpation in the epigastrium and mesogastrium, without rebound tenderness or a positive Murphy sign. No other abnormalities were observed on physical examination. Initial laboratory test results showed an amylase level of 1133 U/L and a lipase level of 2004 U/L, which, along with the epigastric pain, led to the diagnosis of acute pancreatitis – her third episode in 5 years.

Endoscopic ultrasound of the pancreas showed focal enlargement of secondary ducts in the head of the pancreas, involving an area measuring approximately 9.8 mm by 6.4 mm. The lesion had regular contours and precise limits, without peripheral trabeculae, vegetating projections on its walls, or peripheral enhancement on Doppler signal, consistent with an intraductal papillary mucinous neoplasm of the secondary duct. The pancreatic parenchyma demonstrated a diffusely hyperechoic and heterogeneous echotexture. Similar findings were observed on abdominal ultrasound and computed tomography (CT). Additionally, the gallbladder showed no wall thickening but exhibited a large amount of heterogeneous, predominantly hypoechoic, amorphous, and mobile content within, suggestive of biliary sludge (Figure 1).

The patient had a history of 2 previous episodes of pancreatitis, each followed by thrombotic microangiopathy (TMA) requiring plasmapheresis. The first episode occurred in 2019 and was associated with thrombocytopenia (platelet count, 63×103/μL) and acute kidney injury (serum creatinine, 3.6 mg/dL). The second episode occurred in 2020, when the hypothesis of atypical hemolytic-uremic syndrome (aHUS) was made. On both occasions, the patient received plasmapheresis and hemodialysis, and during the 2020 hospitalization, blood transfusions were needed. At that time, complement C3 (65 mg/dL; reference range, 81–157 mg/dL) and C4 (10 mg/dL; reference range, 13–39 mg/dL) were below the reference range. Autoantibody screening, including anticardiolipin antibodies, cryoglobulins, lupus anticoagulant, antinuclear antibodies, anti–double-stranded DNA antibodies, and antineutrophil cytoplasmic antibodies, was negative. Immunoglobulin G subclass 4 levels were within the reference range. Tests for Shiga toxin and Escherichia coli O157: H7 were negative, and a disintegrin and metalloproteinase with thrombospondin motifs 13 activity was 125%.

An aHUS genetic panel, obtained during a previous admission, revealed the following heterozygous mutations: (1) a deletion of uncertain clinical significance involving the 5′ untranslated region (UTR) and exon 1 of the complement factor H-related protein (CFHR3) gene, corresponding to the 3′ UTR of the complement factor H (CFH) gene, in heterozygous state, with a possible association with susceptibility to aHUS (Online Mendelian Inheritance in Man [OMIM]: 605336), which exhibits autosomal recessive or dominant inheritance; (2) a variant of uncertain clinical significance in the complement factor I (CFI) gene (chromosome 4, c.548A>G, p.His183Arg), associated with susceptibility to aHUS 3 (OMIM: 612923) and CF1 deficiency (OMIM: 610984), with autosomal dominant or recessive inheritance; and (3) a variant in the complement 3 (C3) gene (chromosome 19, c.4855A>C, p.Ser161Arg), associated with susceptibility to aHUS 5 (OMIM: 612925) and C3 deficiency (OMIM: 613779), with autosomal dominant or recessive inheritance. Together, these results corroborated the diagnosis of pancreatitis-induced TMA-aHUS.

During the current 2024 hospitalization, initial laboratory test results showed normocytic and normochromic anemia (hemoglobin, 8.9 g/dL; mean corpuscular hemoglobin, 30 pg; mean corpuscular volume, 93.3 fL; mean corpuscular hemoglobin concentration, 31.1 g/dL), lymphopenia (lymphocyte count, 480 cells/mm3), and thrombocytopenia (platelet count, 88×103/mm3) with schistocytes noted on peripheral blood smear analysis. Additional studies demonstrated normal to mildly decreased fibrinogen (187 mg/dL), lactate dehydrogenase, 265 U/L; haptoglobin, 96 mg/dL; ferritin, 303 μg/L; D-dimer, 1875 ng/mL; international normalized ratio, 1.2; creatinine, 0.57 mg/dL; amylase, 1133 U/L; and lipase, 2004 U/L. Kidney function, liver and canalicular enzymes, and bilirubin levels were normal. The patient was admitted to the intensive care unit where she received plasmapheresis for TMA-aHUS. She also received corticosteroid therapy because of the development of pruritus and papules on her back during the plasmapheresis procedure. A viral panel, ordered to investigate the flu-like symptoms, was positive for metapneumovirus.

She was transferred from the intensive care unit after 2 days. On the third day of hospitalization, she developed a fever of 38.3°C (while her C-reactive protein level remained between 2 and 4 mg/dL) and experienced 2 episodes of desaturation, accompanied by bilateral crackles at the lung bases. This required supplemental O2 (1 L/min) to maintain SpO2 at 92%. A chest CT scan revealed findings compatible with lobar bronchopneumonia of the left lower lobe; CT angiography was negative for pulmonary embolism. Her C-reactive protein level subsequently increased to 12.5 mg/dL. Ceftriaxone (1 g every 12 hours) was initiated. The patient was successfully weaned from supplemental O2 on the third day of antibiotic therapy.

Over the following days, the patient’s amylase and lipase levels decreased (amylase, 95 U/L; lipase, 135 U/L), but she developed a slight increase in liver enzymes (aspartate aminotransferase, 91 U/L; alanine aminotransferase, 107 U/L; alkaline phosphatase, 46 U/L; and gamma-glutamyl transferase, 93 U/L). At this time, she reported having abdominal discomfort on deep palpation and percussion of the epigastrium, which was followed by a further increase in serum enzyme levels, leading to the diagnosis of cholecystitis. Serologies for hepatitis A, B, and C, as well as cytomegalovirus, HIV 1–2, dengue virus, and Treponema pallidum were negative.

The patient underwent laparoscopic cholecystectomy. Intraoperative cholangiography was negative for choledocholithiasis. Histopathological examination of the gallbladder revealed the presence of Actinomyces spp. colonies (Figure 2) and changes in the mucosa and muscular layers consistent with chronic cholecystitis. Cultures were not performed. Postoperative magnetic resonance cholangiography showed a hypervascularized nodule in segment VII of the liver (0.9 cm) and sparse dilation of some secondary pancreatic ducts (up to 0.6 cm) in the pancreatic head, some of which communicated with the main duct. The patient recovered well postoperatively. Her liver and canalicular enzyme levels peaked 2 days after surgery (aspartate aminotransferase, 699 U/L; alanine aminotransferase, 737 U/L; alkaline phosphatase, 272 U/L; and gamma-glutamyl transferase, 603 U/L) and subsequently decreased over the next 6 days, remaining stable thereafter. She was discharged on postoperative day 4 in good general condition. Oral amoxicillin (500 mg 4 times daily for 3 months) was prescribed at discharge. During a 1-year follow-up period, she experienced no further episodes of pancreatitis or elevations on liver and canalicular enzymes. Figure 3 illustrates the trends in the levels of liver, canalicular, and pancreatic enzymes during her hospitalization and initial outpatient follow-up.

Discussion

Actinomycosis is an uncommon subacute to chronic infection caused by the slow growing, anaerobic gram-positive bacilli belonging to the genus Actinomyces. While primarily commensal inhabitants of the oral cavity and intestinal tract, these bacteria can transition to pathogenic states upon invasion of compromised tissue barriers [1,2,20]. Several species cause disease in humans; the most common is Actinomyces israelii. Although actinomycosis can affect various regions of the body, the cervicofacial area is the most common site of infection, followed by abdominal and thoracic involvement [2,3,7,21,22].

Gastrointestinal actinomycosis commonly involves the appendix, cecum, and colon. Predisposing factors for abdominal actinomycosis include recent abdominal surgery, trauma, neoplasia, or perforated viscus. Depending on the affected site, symptoms can range from dysphagia (esophagus) to nonspecific abdominal pain, weight loss, and fever. On the gallbladder, the infection is believed to spread either retrogradely from the duodenum or via hematogenous dissemination, often involving disruption of the biliary tract mucosa, in the setting of prior inflammation, surgery, or fistula formation, which allows the Actinomyces spp. to invade and establish infection in the gallbladder or biliary ducts [23,24]. This local invasiveness, coupled with the bacteria’s slow growth characteristics, can lead to delayed clinical presentations, sometimes occurring months or even years after the initial insult [6,23,25]. In the present case, our patient had a total of 3 cholecystitis diagnosis, all of them associated with pancreatitis and TMA-aHUS, creating the appropriate disruption of the biliary tract mucosa for colonization by Actinomyces spp.

Actinomyces infection is a rare but documented cause of cholecystitis and pancreatitis, with several case reports describing Actinomyces spp. isolated from bile or gallbladder tissue in patients with recurrent or atypical cholecystitis [15,23]. Clinically, actinomycotic cholecystitis can mimic acute and chronic cholecystitis, and even gallbladder carcinoma, further complicating diagnosis [17,26,27]. In fact, until 2022, only 23 cases of Actinomyces-related cholecystitis were described, mostly due to A. naeslundii, but also by A. islaelii infection. Some were cases of co-infection between Actinomyces spp. and Pseudomonas aeruginosa or Haemophilus aphrophilus [12,13,28]. In our case, although no Actinomyces spp. culture was performed, our histopathological analysis showed gram-positive bacilli on Gram stains and sulfur granules on hematoxylin and eosin staining, confirming the presence of such microorganisms.

In general, imaging findings of abdominopelvic actinomycosis are characterized by strong enhancement in the solid portion of the mass, small rim-enhancing abscesses within the mass, and extensive inflammatory extension beyond normal tissue planes. On gallbladder ultrasound, actinomycosis can present as a hypoechoic mass replacing the gallbladder lumen, often engulfing a gallstone. On contrast-enhanced CT, findings include a heterogeneously enhanced, markedly thickened gallbladder wall with disrupted luminal surface enhancement, forming a mass-like lesion. There is typically extensive pericholecystic infiltration, which may extend into adjacent abdominal wall musculature. These features can closely mimic gallbladder carcinoma, making differentiation challenging without histopathological confirmation [5,17,29,30].

In our case, endoscopic ultrasound of the pancreas showed a diffusely hyperechoic and heterogeneous echotexture, followed by focal enlargement of secondary ducts in the head of the pancreas with regular contours and precise limits, without peripheral trabeculae, vegetating projections on its walls, or peripheral enhancement on Doppler signal, consistent with an intraductal papillary mucinous neoplasm of the secondary duct. The investigation of the gallbladder showed no wall thickening but exhibited a large amount of heterogeneous, predominantly hypoechoic, amorphous, and mobile content within, suggestive of biliary sludge (Figure 1). Similar findings were observed on abdominal ultrasound and CT scan. Given the rarity of gallbladder actinomycosis, these findings should prompt consideration of the diagnosis when imaging reveals a mass engulfing a stone, marked wall thickening, and extensive infiltration, especially in the absence of typical risk factors for malignancy [15,17,21,29,31–33].

Diagnosis often involves a combination of clinical presentation, laboratory tests, and imaging studies. Leukocytosis with elevated neutrophils and elevated inflammatory markers such as C-reactive protein are common. The gold standard for diagnosis is tissue biopsy with anaerobic culture. Gram stain analysis of actinomycosis cases may reveal characteristic branched, beaded, gram-positive filamentous bacilli, often accompanied by sulfur granules. These sulfur granules can also be observed in histopathological examinations, appearing as basophilic masses with eosinophilic terminals on hematoxylin and eosin staining. In the present case, such sulfur granules and gram-stained bacilli were present on the histopathological specimens of the gallbladder, which also presented (1) varying degrees of mucosal hyperplasia and transmural fibrosis; (2) xanthomatous histiocytes (cholesterolosis) in the sub-epithelial position; and (3) small invaginations in the gallbladder wall into the muscular layer consistent with Rokitansky-Aschoff sinuses. These findings are consistent with chronic cholecystitis [27,34,35].

They are also commonly present in xanthogranulomatous cholecystitis (XGC), a rare non-malignant inflammatory disease of the gallbladder, primarily affecting older individuals. The pathogenesis of XGC involves chronic inflammation and the accumulation of lipid-laden (foamy) macrophages within the gallbladder wall. The process is thought to begin with rupture of Rokitansky-Aschoff sinuses or mucosal ulcerations in the gallbladder wall, leading to chronic inflammatory changes, bile extravasation, and macrophage lipid engulfment (xanthomatous cells). This response is characterized by infiltration of foamy macrophages, T lymphocytes (predominantly CD8+), multinucleated giant cells, and fibrosis. While Actinomyces spp. can cause chronic inflammatory changes, most cases of XGC are associated with other bacteria, such as Escherichia coli. Actinomyces is not routinely identified in histopathologic or microbiologic studies of XGC [14,27,36].

Pathologies of the gallbladder and biliary system present a significant diagnostic dilemma due to the similarity of the clinical and histopathological findings, including those found with Actinomyces ssp. infections. Conditions ranging from common acute calculous cholecystitis to rare inflammatory processes such as tuberculousis and XGC often manifest with similar clinical presentations, including right upper quadrant pain, pyrexia, and leukocytosis. Radiologically, the cardinal finding of gallbladder wall thickening is notoriously nonspecific, complicating the crucial differentiation between these benign inflammatory states and gallbladder carcinoma, which XGC frequently mimics. This broad differential spectrum is further complicated by the inclusion of hepatobiliary diseases, such as primary sclerosing cholangitis and cholangiocarcinoma, as well as the urgent need to exclude life-threatening emergencies, such as emphysematous cholecystitis, pyogenic abscess, and perforation with peritonitis [37–41].

Additionally, pancreatic actinomycosis is a rare condition characterized by a slow-growing mass with associated biliary and pancreatic duct obstruction, often mimicking malignancy and chronic pancreatitis. Its association with intraductal papillary mucinous neoplasm is a potential correlation due to shared characteristics such as obstructive features and chronic inflammation. The overlap in clinical presentation expresses the importance of considering actinomycosis in the differential diagnosis of patients with intraductal papillary mucinous neoplasm. On the other hand, pancreatic actinomycosis is also often associated with previous pancreatic surgeries or endoscopic stenting and chronic pancreatitis. In any circumstances, early diagnosis through endoscopic ultrasound-guided fine-needle aspiration is crucial for differentiating pancreatic actinomycosis from chronic pancreatitis and other pancreatic malignancies, ensuring appropriate treatment and avoiding unnecessary surgical intervention [15,31,42].

Interestingly, along with cholecystitis and pancreatitis, our patient presented clinical and laboratorial manifestations of TMA-aHUS. This group of syndromes, characterized by microangiopathic hemolytic anemia, thrombocytopenia, and end-organ damage, has diverse etiologies, including autoimmune diseases, neoplasms, and infections. However, bacterial infections associated with TMA-aHUS are typically caused by agents such as Shiga toxin–producing E. coli, rather than Actinomyces. Nonetheless, severe infections, such as actinomycosis bacteremia, may act as a precipitating “second hit” in predisposed individuals. This is driven by a systemic inflammatory activation, involving cytokine release and neutrophil extracellular trap formation, which collectively promotes the endothelial injury and microthrombosis fundamental to TMA-aHUS. Therefore, given the preceding observations and discussion, systemic inflammation conditions such as pancreatitis and the Actinomyces spp. bacteremia could, theoretically, contribute to or be the consequence of TMA-aHUS development in a multifactorial setting, especially in patients with underlying risk factors [43–45].

The correlation between complement component 3 (C3), complement factor I (CFI), and complement factor H-related protein 3 (CFHR3) with TMA is fundamentally linked to the pathogenesis of aHUS, a complement-mediated form of TMA. Genetic abnormalities in these crucial components of the alternative complement pathway lead to uncontrolled complement activation, resulting in endothelial damage and microthrombi [45,46].

Our genetic analysis identified 2 significant findings related to the pathogenesis of TMA-aHUS. The first is the p.(His183Arg) missense variant in the CFI gene (OMIM: 612923; OMIM: 610984). This is a loss-of-function mutation in a key regulatory protease, which impairs the degradation of C3b. This failure of inhibition leads to excessive complement activation, membrane attack complex (C5b-9) formation, and subsequent endothelial injury, consistent with aHUS. This variant is often heterozygous with incomplete penetrance, requiring other triggers. The second finding was a CFHR3 5’UTR/CFH 3’UTR deletion (OMIM: 605336), which typically involves a homozygous codeletion with CFHR1. This abnormality predisposes to acquired complement dysregulation through a strong association with the formation of anti–factor H autoantibodies. These autoantibodies neutralize the primary complement inhibitor (factor H), leading to an uncontrolled alternative pathway activation and TMA [45,47–49].

Conversely, the noted C3 variant p.(Ser1619Arg) is currently classified as a variant of uncertain significance (OMIM: 613779) and is not recognized as pathogenic in the published literature. Although other C3 mutations (typically gain-of-function) are known to cause aHUS by making C3b resistant to inactivation, this specific variant requires further functional studies to determine its clinical pathogenicity. Therefore, although the mechanisms vary – from genetic variants causing hereditary hyperactivation (C3, CFI) to a genetic predisposition for an acquired autoimmune response (CFHR3/CFHR1 deletion) – all converge on the alternative pathway hyperactivation that drives TMA [45,46,50].

A combined approach of antibiotic therapy and surgical intervention is effective in curing 90% of actinomycosis cases. Antibiotic treatment typically involves intravenous penicillin G (18–24 million units/day) for 2 to 6 weeks, followed by oral amoxicillin (500–750 mg) 3 to 4 times daily for 6 to 12 months, with beta-lactams and cephalosporins serving as reasonable alternatives. For penicillin-allergic patients, clindamycin, macrolides, or doxycycline are acceptable options. In polymicrobial infections, a combination of metronidazole and a beta-lactamase inhibitor can be considered, but metronidazole is not effective against Actinomyces spp. The duration of therapy can be shortened (less than 3 months) if surgical resection of the infected site is performed in less bulky disease [2,51,52]. The patient in the present case, who had already received a 7-day course of 1 g ceftriaxone twice daily and undergone elective cholecystectomy, agreed to treatment with an extended course of amoxicillin (500 mg, 4 times daily) for 3 months.

Monitoring treatment response is essential, with imaging studies such as CT or MRI used to assess resolution of the infection. In cases of incomplete response or treatment failure, a change in antibiotic regimen or surgical debridement can be necessary. It typically involves incision and drainage of abscesses, decompression of closed spaces, and complete or partial excision of the affected tissue. Complications, including abscess formation, osteomyelitis, and central nervous system involvement, can arise during the treatment [2,5,6,15,20,53]. In the present case, following surgery and antibiotic treatment, the patient experienced complete clinical improvement, with resolution of hepatic and pancreatic enzyme abnormalities and inflammatory markers.

Conclusions

Here, we report an unusual case of a 26-year-old woman presenting with her third episode of pancreatitis, which was followed by cholecystitis and TMA-aHUS. Histopathological investigation of specimens obtained after her cholecystectomy revealed microscopic alterations consistent with chronic cholecystitis, the presence of sulfur granules on hematoxylin and eosin staining, and colonies of gram-positive bacilli consistent with Actinomyces spp. We also present data from previous hospitalizations showing the presence of heterozygous mutations in the CFHR3 and CFI genes, which are involved in the control of complement activation and have been previously associated with the occurrence of TMA-aHUS.

The association between Actinomyces and TMA-aHUS is neither direct nor classically recognized in medical literature. In the present case, following a chronological line of events, we postulated that the systemic inflammation caused by the initial acute pancreatitis episode in 2019, in association with predisposing gene mutations, led to TMA-aHUS and acute cholecystitis, and consequently, mucosal inflammation and structural alterations of the gallbladder and biliary duct. The second episode of pancreatitis associated with aHUS in 2020 (when the gene mutations were investigated) further injured the compromised organs and facilitated their colonization by Actinomyces spp. The now-colonized gallbladder entered a stage of chronic inflammation, subsequently observed on histopathological specimens, leading to the formation of biliary sludge and the onset of the most recent pancreatitis and cholecystitis episodes in 2024.

Achieving the diagnosis and correct treatment of these conditions required 5 years, 3 hospitalizations, a considerable number of laboratory tests and imaging studies, numerous procedures including a cholecystectomy, and prolonged antimicrobial therapy, as well as significant psychological distress for the patient. Taken together, the findings described in this case report indicate the need for early diagnosis and timely initiation of appropriate antimicrobial therapy, along with surgical intervention, when necessary, to prevent the recurrence of clinical manifestations and sustain quality of life.