Infectious Diseases 2026

Thoracic actinomycosis is an uncommon, chronic bacterial infection caused predominantly by Actinomyces species. It can produce pulmonary consolidation, abscess formation and extension across tissue planes into the chest wall, and may closely mimic tuberculosis or malignancy. A young woman in her 20s, previously fit and well, presented with a 2–3-week history of left posterolateral chest wall pain followed by progressive swelling, intermittent cold sensations, 2–3 kg weight loss, and recent cough with haemoptysis. She had experienced two earlier episodes of left-sided pneumonia with similar symptoms, treated with short courses of antibiotics. Examination revealed a large (>10 cm), warm, firm, non-fluctuant swelling over the left posterolateral chest wall. Blood tests showed a marked inflammatory response (WCC 16.2 ×10⁹/L, CRP 168–169 mg/L) and microcytic anaemia. CT demonstrated consolidation in the superoposterior left lower lobe with perifissural nodules, volume loss, reactive nodes, and a contiguous chest wall collection. Tuberculosis was considered. Ultrasound-guided biopsy showed a heterogeneous, septated mass with necrosis. AFB staining, tuberculosis PCR and mycobacterial culture (at eight weeks) were all negative. Histology demonstrated granulation tissue and abscess formation with filamentous Gram-positive aggregates suggestive of Actinomyces. The patient improved on intravenous co-amoxiclav and completed a prolonged course of oral antibiotics, later adjusted to cefalexin and then doxycycline on microbiology advice. This case highlights the diagnostic challenge of thoracic actinomycosis presenting with pulmonary consolidation and chest wall involvement. Histological examination was crucial in establishing the diagnosis. Actinomycosis should be considered when chronic pulmonary disease extends across tissue planes into the chest wall, particularly after tuberculosis has been excluded.

Dr Mohsin Fayyaz is a GMC-registered doctor currently working as a Rotational Clinical Fellow in Stroke Medicine at Salford Royal Hospital, Northern Care Alliance NHS Foundation Trust. He has over six years of clinical experience across Stroke Medicine, Trauma & Orthopaedics, Emergency Medicine and General Surgery. His clinical interests include acute and emergency care, stroke medicine, and the recognition and management of complex infectious and respiratory presentations. He has been involved in the clinical assessment and management of this case and has a particular interest in improving the recognition of uncommon thoracic infections and their ability to mimic other clinical conditions.