PA follows a chronic course. Patients may present with constitutive symptoms like fatigue, fever, night sweats, loss of appetite and weight. While dyspnea, non-productive cough, and chest pain may indicate a thoracic pathology, these symptoms are neither specific for PA. On the other hand, affected individuals may claim purulent expectoration or hemoptysis. Pus may also be discharged through sinus tracts and typically contains sulphur granules. The most common symptoms are cough, expectoration and chest pain, which are experienced by 71, 55, and 41% of affected individuals, respectively [3].

In recent decades, a general trend towards a less dramatic, even subclinical course of the disease has been observed [4]. Nowadays, the incidental observation of pulmonary shadowing is often the first indicator of lung diseases like PA. Due to limited awareness and because of the disease' epidemiology, physicians frequently misdiagnose PA as malignancy, lung abscess, or tuberculosis [5] [6].

As has been implied above, thoracic imaging often reveals first evidence of a pulmonary mass consistent with PA. Both plain radiography and computed tomography scans may allow to assess the extension of the disease. Images most commonly comprise hyperdense regions corresponding to areas of air-space consolidation [7]. The detection of central cavitation and satellite nodules as well as peripheral enhancement due to fibrotic demarcation may aid to distinguish PA from lung cancer [8]. Additional, yet non-specific findings comprise hilar or mediastinal lymphadenopathy, bronchiectasis within the consolidated area, pleural thickening and pleural effusion. Although further clarification may be achieved performing bronchoscopy, only the isolation of Actinomyces spp. from otherwise sterile sites is diagnostic of actinomycosis. In order to do so, tissue samples have to be obtained by means of lung biopsy. This procedure is generally performed percutaneously under ultrasound or computed-tomography guidance, but may also be realized during open surgery. There is little consensus regarding the usability of transbroncheal biopsy samples for bacteriological testing [4] [1]. Obtained specimens should not only be subjected to bacteriological analysis, but also be evaluated histopathologically to rule out neoplasms. Of note, the bacteriological examination of sputum is a poorly sensitive measure since positive results may result from the mere colonization of mucous membranes by Actinomyces spp. [9].

Laboratory analyses of blood samples should be carried out to evaluate the overall condition of the patient. PA is generally associated with mild leukocytosis and anemia as well as mild to moderate enhancement of acute phase parameters [10].

Pulmonary actinomycosis (PA) is a rare infectious disease whose etiological agents pertain to the genus Actinomyces. The most common species to cause the disease is Actinomyces israelii [1], but a variety of other representatives of this genus have also been associated with the disease. Actinomyces spp. form part of the commensal flora of the oropharynx, gastrointestinal and urogenital tract, and causative pathogens reach the respiratory tract upon the aspiration of oropharyngeal or gastrointestinal secretions [2]. Tobacco consumption, alcohol abuse, a poor oral hygiene as well as underlying respiratory disorders predispose for PA [3].

Affected individuals may present non-specific respiratory and general symptoms that may mimic more severe diseases like cancer and tuberculosis. However, PA patients respond well to treatment with penicillin. The antibiotic is generally given over the course of two weeks and causes a rapid improvement of the patient's condition.

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