Pulmonary actinomycosis is a chronic suppurative granulomatous disease caused by anaerobic Actinomyces israelii infection in the lungs. This bacterium is a normal resident in the oral cavity, dental caries, and tonsillar crypts of healthy individuals. Most cases result from poor oral hygiene, where secretions containing actinomycete granules are inhaled. It can also arise from hematogenous spread or direct extension of abdominal lesions. Under anaerobic conditions, this bacterium forms spherical colonies on agar culture. In tissues, it appears as yellow granules, commonly referred to as "sulfur granules," which are composed of tangled filaments. Microscopically, these are Gram-positive filamentous clusters measuring 0.5–1.0 μm, with radiating peripheral filaments and club-shaped swollen ends.

bubble_chart Pathological Changes

Lung infection begins with bronchitis, featuring suppurative granulomas and the formation of multiple small abscesses. Sulfur granules can be seen within the abscesses, surrounded by epithelioid cells, multinucleated giant cells, eosinophils, and plasma cells, with fibrosis further outward. The lesion involves the pleura, leading to pleuritis or empyema, and may perforate the chest wall to form fistulas. The hallmark of this disease is the simultaneous occurrence of destruction and proliferation, where scarring and healing coexist with continued expansion into surrounding tissues.

bubble_chart Clinical Manifestations

The onset is usually insidious, beginning with low-grade or irregular fever and cough, accompanied by the production of small amounts of mucoid sputum. As the lesions progress and multiple abscesses form in the lungs, symptoms worsen. High fever, severe cough, and copious mucopurulent sputum may occur, often with blood-streaked sputum or massive hemoptysis, accompanied by weakness, night sweats, anemia, and weight loss. If the disease extends to the pleura, it can cause severe chest pain. Invasion of the chest wall may lead to subcutaneous abscesses and fistula formation, frequently discharging pus mixed with bacterial debris. The surrounding tissue of the fistula may show pigmentation. After healing of the fistula opening, new fistulas may appear nearby. If the mediastinum is involved, it can result in difficulty breathing or swallowing, and severe cases may be fatal. Signs of lung abscess and pleural effusion may also be present.

Irregular patchy infiltrative shadows are scattered in one or both lungs, which may coalesce into consolidation with irregular lucent areas and may be accompanied by pleural effusion. When the lesions extend to the ribs or spine, signs of osteomyelitis may be observed, with destruction of the ribs or vertebrae.

bubble_chart Diagnosis

In the early stages, there are no characteristic changes clinically or radiographically, making diagnosis difficult. Confirmation primarily relies on microbiological and histological examinations. The presence of sulfur granules in pus, sputum, or tissue from the fistula wall, or the isolation of pathogenic bacteria through anaerobic culture can confirm the diagnosis.

This disease is easily confused with pulmonary subcutaneous nodules, bronchogenic carcinoma, and lung abscess; it closely resembles nocardiosis in clinical and radiographic manifestations as well as the morphology of the pathogenic bacteria, necessitating careful differentiation. Nocardia often invades the central nervous system, rarely forms chest wall fistulas, and does not produce sulfur granules in sputum, being an aerobic bacterium.

bubble_chart Treatment Measures

Penicillin G is highly effective for treatment. The dose should be large, typically 2 to 10 million units per day administered intravenously, adjusted based on the condition. The dose can be reduced once the condition stabilizes. The treatment course is long, usually lasting 1 to 3 months, or continued until the lesion resolves. If the response to penicillin is unsatisfactory, high-dose sulfonamides (achieving a blood concentration of 5–10 mg%) may be added to enhance efficacy. For patients allergic to penicillin or those who do not respond to treatment, alternatives include streptomycin, erythromycin, lincomycin, tetracycline, and cephalosporin antibiotics. Abscesses in the chest wall or empyema must be incised and drained. Surgical resection may be considered for actinomycotic pulmonary granulomas, fibrosis, bronchiectasis, chest wall or rib lesions, or fistulas that do not heal with prolonged treatment.