A40-28 Uncommon Dual Presentation of Dipnech and Chronic Hypersensitivity Pneumonitis in an Elderly Female

Abstract Introduction Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) is a rare pulmonary disorder characterized by abnormal proliferation of pulmonary neuroendocrine cells. Its clinical and radiologic features often mimic hypersensitivity pneumonitis (HP), an immune-mediated interstitial lung disease. The coexistence of both entities is uncommon and poses diagnostic and management challenges. Here, we present a case of a patient with HP who was subsequently diagnosed with DIPNECH, highlighting the complexity of diagnosis. Case Presentation An 86-year-old woman with hypertension, chronic kidney disease presented with progressive dyspnea and hypoxia. High-resolution CT demonstrated mosaic attenuation with air trapping and multiple pulmonary nodules, suggestive of HP. Hypersensitivity serologies were negative, and total IgE was 20 IU/mL. Bronchoscopy revealed normal bronchial mucosa, and bronchoalveolar lavage (BAL) showed predominantly macrophages with negative cultures and cytology. Pulmonary function testing revealed a mixed obstructive and restrictive pattern with moderate reduction in gas transfer. Given the inconclusive results, the patient underwent a surgical lung biopsy. The lower lobe showed interstitial fibrosis, emphysema, respiratory bronchiolitis, and microscopic honeycombing, consistent with chronic HP or nonspecific interstitial pneumonitis. The upper lobe demonstrated multifocal, well-differentiated neuroendocrine tumors, positive for CK8/18, synaptophysin, TTF-1, chromogranin, and INSM1, with Ki-67 3%, diagnostic of DIPNECH. Autoimmune serologies were negative, and no specific antigen exposure was identified. She was started on four weeks of prednisone taper, followed by mycophenolate mofetil, with significant symptomatic improvement at follow-up. Discussion This case underscores the diagnostic complexity when DIPNECH and HP coexist, as both can present with small airway disease, mosaic attenuation, and air trapping. HP typically manifests with diffuse ground-glass opacities, centrilobular nodules, and air trapping, whereas DIPNECH more often shows peribronchiolar nodules in the lower lobes with bronchial wall thickening. HP results from antigen-driven immune injury, while DIPNECH represents idiopathic neuroendocrine proliferation. Their coexistence may reflect overlapping or sequential disease processes. Management of DIPNECH is largely symptomatic; somatostatin analogs may improve cough and lung function. In HP, antigen avoidance and corticosteroids remain the mainstay of therapy, with additional benefit from immunosuppressants such as azathioprine or mycophenolate, and antifibrotic agents like nintedanib in progressive fibrosing ILD. Recognizing such overlap is crucial, as treatment should be guided by the dominant pathology. Conclusion This case highlights the rare coexistence of DIPNECH and hypersensitivity pneumonitis, emphasizing the need for a multidisciplinary approach and careful integration of the data to differentiate overlapping features. Figure: High-resolution CT chest showing mosaic attenuation pattern with areas of air trapping This abstract is funded by: None