Pulmonary Actinomycosis Mimicking Lung Malignancy in an Underserved Patient

Introduction/Background

Pulmonary actinomycosis is a rare and often misdiagnosed infection that can closely mimic malignancy due to its chronic presentation and radiographic findings. We present a case of a 65-year-old male with a significant smoking history who exhibited progressive weight loss, fatigue, and a productive cough with concerning imaging findings, including spiculated pulmonary nodules, mediastinal adenopathy, and a hepatic lesion. Initial clinical suspicion was high for malignancy; however, biopsy and microbiological studies revealed an Actinomyces odontolyticus infection. This case emphasizes the importance of considering infectious etiologies, particularly actinomycosis, in patients with radiologic and clinical features suggestive of malignancy, thereby preventing unnecessary invasive procedures and ensuring timely antimicrobial therapy.

Clinical Presentation

A 65-year-old male with a 29-pack-year smoking history presented with generalized fatigue, weakness, and unintentional weight loss (10–15 lbs over 4–5 weeks). He reported a productive cough with brown sputum and a decreased appetite, noted by his relatives. He had a recent bicycle accident with possible aspiration. His worsening cough impaired ambulation, but he denied nausea, vomiting, palpitations, fever, or chills. Examination revealed a thin, cachectic man with bilateral lower leg edema. Labs showed hyponatremia, microcytic anemia, leukocytosis, elevated ferritin, low TIBC, and reactive thrombocytosis. Imaging revealed spiculated right upper lobe pulmonary nodules, mediastinal and axillary adenopathy, a hepatic lesion, and a large right-sided loculated pleural effusion. EKG showed rapid atrial flutter. Biopsy revealed fibrosis and inflammatory infiltrates. Blood cultures grew Actinomyces odontolyticus, confirming pulmonary actinomycosis. Thoracentesis drained 220 mL of frank pus, and CT surgery ruled out thoracotomy/decortication. Infectious disease recommended outpatient ceftriaxone or oral penicillin with a favorable prognosis.

Results/Discussion

This case highlights the diagnostic challenge of differentiating pulmonary actinomycosis from malignancy, particularly in patients with significant smoking histories and radiographic findings that are concerning for cancer. The presence of spiculated pulmonary nodules, mediastinal and axillary adenopathy, and a hepatic lesion initially raised strong suspicion for a neoplastic process. Literature has also discovered that nearly 30% of actinomycosis cases are initially misdiagnosed as lung/hepatic malignancies. Therefore, timely recognition of actinomycosis and a high index of suspicion of infectious pathogens by clinicians can prevent unnecessary invasive procedures and lead to effective treatment with prolonged antibiotic therapy over the course of various weeks, thus ensuring a favorable prognosis.

Pulmonary actinomycosis can closely resemble lung cancer, especially in patients with significant smoking histories, due to its chronic symptoms and radiologic findings (e.g., spiculated nodules, mediastinal adenopathy, hepatic lesion). Timely diagnosis prevented unnecessary invasive procedures and allowed for appropriate antimicrobial therapy (ceftriaxone or oral penicillin), leading to a favorable prognosis.