Miliary pattern on chest imaging caused by adenocarcinoma

A 55-year-old, nonsmoking woman without underlying disease presented to the emergency department with a 3-month history of productive cough, dyspnea, night sweats and 4 kg weight loss. On examination, her temperature was 36.8°C, heart rate was 75 beats per minute, blood pressure was 92/73 mm Hg, and respiratory rate was 15 breaths per minute. Her peripheral oxygen saturation was 95% on 3 L/min of oxygen. We heard bilateral inspiratory crackles on chest auscultation and did not observe any clubbing of her digits. Her eosinophil count was 7.7% (normal 0%–6%) and her C-reactive protein level was normal. Chest radiography and computed tomography showed a miliary pattern of many small nodules throughout all lung fields (Figure 1 and video Appendix 1, available at www.cmaj.ca/lookup/doi/10.1503/cmaj.211410/tab-related-content) Real -time polymerase chain reaction (RT-PCR) testing for SARS-CoV-2 was negative.

Our differential diagnoses included tuberculosis, fungal infection and malignant disease. We suspected pulmonary tuberculosis, but 3 sputum smears were negative for acid-fast bacilli, and cultures of sputum and bronchoalveolar lavage fluid were negative for Mycobacterium tuberculosis and fungi. Bronchoscopic biopsy of the right upper lung showed highly differentiated primary lung adenocarcinoma. Whole-body computed tomography and magnetic resonance imaging of the brain did not find any evidence of metastasis outside the lung. Testing with RT-PCR revealed exon 19 deletion in the epidermal growth factor receptor (EGFR). The patient was treated with osimertinib, an EGFR tyrosine kinase inhibitor. One month later, her resting oxygen requirement had decreased to 1 L/min and the size of the pulmonary nodules had decreased.

Adenocarcinoma with mutations of EGFR is observed in 10%-20% of non-Asian patients with non-small cell lung cancer. It is more frequent in women, nonsmokers or light smokers, and in people of Asian descent.1 The presence of EGFR mutations in lung adenocarcinoma is associated with miliary metastases. 2,3 Compared with chemotherapy, EGFR tyrosine kinase inhibitors dramatically improve the response rates and overall survival of patients with advanced non–small cell lung cancer and EGFR mutations.1,4 Thus, molecular screening after diagnosing lung adenocarcinoma is necessary to identify targetable oncogenic alterations.

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