A Rare Spread: Case Report of Miliary Pattern in Primary Lung Adenocarcinoma With Simultaneous Cavitary Lesions

Abstract Miliary patterns in chest imaging pose a diagnostic challenge due to their diverse etiologies, including infectious and non-infectious causes. We report an uncommon presentation of primary lung adenocarcinoma with miliary spread and cavitary lesions. A 46-year-old male presented with a several months’ history of dry, non-productive cough and dyspnea. Initial chest x-ray revealed a left lower lobe opacity along with innumerable miliary lesions scattered throughout bilateral lung fields. A thorough infectious workup was unrevealing, including a thorough rule out of TB. Subsequent CT imaging showed a necrotic/cavitating core within the left lower lobe lesion, along with sclerotic lesions in the T6 and T11 vertebral bodies, raising suspicion for a malignant process. A biopsy of the left lower lobe lung lesion confirmed the diagnosis of pulmonary adenocarcinoma. Genetic testing revealed an EGFR p.E746 A750 deletion. An MRI of his brain revealed 28 metastatic lesions. Gamma Knife stereotactic radiosurgery was initiated for the brain metastases. The patient received a single cycle of chemotherapy consisting of carboplatin, pemetrexed, and pembrolizumab before transitioning to osimertinib, targeting the EGFR mutation. A follow-up CT of the chest showed radiographic evidence of pulmonary disease diminution, with a reduction in the left lower lobe consolidation and a decrease in area of cavitation/necrosis, along with the resolution of the previous miliary pattern. Miliary pulmonary lesions are due to lymphohematogenous spread, which is a rare finding with initial presentation of primary lung cancer occurring in around 2.5% of cases. A differential diagnostic categorization is broken into infectious and noninfectious groups. Common infectious etiologies include tuberculosis and fungal infections but rarely can occur in viral or parasitic infections. Non-infectious etiologies include malignancy, inflammatory, autoimmune, and drug reactions. Adenocarcinoma is the most common pulmonary malignancy presenting as miliary spread. Osimertinib is a 3rd generation EGFR inhibitor that has improved penetration to the brain compared to earlier iterations. The recent ADAURA trial showed improved 5-year survival rates with inclusion of Osimertinib in stages II to IIIa. While the early improvements noted in advanced stage case give optimism, frequent monitoring is necessary for optimal individualized treatment approaches.