Letter to the Editor: Abdominal Actnomycocsis: Great Simulator

Case Report

A 90-year-old female with a history of laparoscopic cholecystectomy (nine years earlier) presented to the emergency department with fever (38.5°C). Symptoms had been progressing for eight days. Laboratory investigations found hemoglobin, 9.4 g/dL; white blood cell count, 14,200/mm³; and C-reactive protein, 187 mg/L. Liver function tests, alpha fetoprotein (1 ng/mL), and carcinoembryonic antigen (1.2 ng/mL) were normal. An enhanced abdominal computed tomography (CT) scan revealed a right liver mixed mass (solid and liquid portion) (Fig. 1). Drainage and biopsy was performed followed by empirical antibiotherapy. The purulent drainage was then sent for bacteriological analysis. The 48-hour aerobic/anaerobic culture returned negative. The biopsies were sent for bacteriological, fungal, and pathology analysis. The pathology sample showed a granulation tissue comprising mostly lymphocytes but no sign of malignancy. An Actinomyces gerencseriae was finally identified by 16S RNA polymerase chain reaction (PCR). The patient then received intravenous amoxicillin regimen (1 g/8 h), followed by oral amoxicillin (1 g three times per day) for three more months.

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FIG. 1.

Arrow shows the mixed liquid and tissue lesion that may mimic a tumor.

Discussion

Human actinomycosis was first described in 1878 by Israel [1]. It is a rare chronic bacterial infection caused by slow-growing Actinomyces. Intra-abdominal locations account for 20% of cases, with oral and cranio-cervical involvement being the most common [2]. The main causative agent is a gram-positive, anaerobic bacillus, represented in 85% of cases by Actinomyces israelii.

Abdominal actinomycosis is a complex diagnosis that can occur at any age. Medical history often includes appendectomy, cholecystectomy, or an intra-abdominal infection. Laparoscopic cholecystectomy with lost gallstones has been reported to be a potential complication leading to actinomycosis [3]. In our case, the patient underwent a cholecystectomy.

Obtaining a definitive diagnosis can be difficult when fever and abdominal pain are the only clinical symptoms, and a long period of time has elapsed between inoculation and diagnosis (up to several years). An early actinomycosis diagnosis is also challenging to make because of the non-specific nature of its signs and symptoms. The laboratory blood tests and radiologic findings are also non-specific [4]. Actinomycosis is also nicknamed the great simulator because it presents as an expanding intra-abdominal fibrous mass, thus mimicking a malignant tumor [4]. Pre-operative biopsy is not routinely done because of technical issues (for example, difficult access to the infection site) and potential peritoneal or parietal contamination. As a result, a confirmatory diagnosis is often difficult, usually leading to surgical resection [5]. The treatment for abdominal actinomycosis is long-term antimicrobial administration, mainly penicillin. However, in case of non-response, surgery can be suggested but must remain limited to the flattening and drainage of the abscess. Radiologic drainage can also be an alternative [6].

The diagnosis and treatment of actinomycosis, especially its abdominal form, is complex. Thus, for any atypical mass, the diagnosis of actinomycosis must be considered.