SESSION TITLE: Fellows Diffuse Lung Disease SESSION TYPE: Fellow Case Reports PRESENTED ON: October 18-21, 2020 INTRODUCTION: Calcitonin gene-related peptide (CGRP) is a neuropeptide found in neuroendocrine cells, lymphoid tissue, blood vessels, and sensory C fibers within pulmonary tissue. It is thought to have a homeostatic effect through epithelial repair, vasoregulation, and an anti-inflammatory effect. CGRP is also expressed in multiple other organ systems, including the nervous system. Recently, inhibition of CGRP within the nervous system has been found to be an effective treatment modality for migraines. We present a case of possible drug induced interstitial disease shortly following initiation of galcanezumab, a monoclonal inhibitor of CGRP. CASE PRESENTATION: A 46 year old female with a history of migraines presented to the pulmonary clinic for evaluation following failure of treatment for presumed community acquired pneumonia. The patient reported 4-6 weeks of progressive cough, dyspnea on exertion, and pleuritic chest pain to the point where she was unable to climb a single flight of stairs. Prior plain chest films were revealing for bilateral scattered interstitial opacities concerning for infectious process. A high resolution CT scan was obtained at the time of pulmonary evaluation revealing a non-UIP pattern. Spirometry was revealing for moderately severe restrictive pattern with severe reduction in DLCO without prior studies for comparison. An ILD questionnaire was performed along with a hypersensitivity pneumonitis panel and extensive serological evaluation for a rheumatologic etiology without a causal finding. Further discussion with patient was revealing for recent initiation of galcanezumab shortly before onset of symptoms. Given her negative evaluation to date and marked functional limitation, she was initiated on prednisone for presumed drug induced etiology and galcanezumab was discontinued. Within two weeks, the patient had a significant improvement in symptoms with normal repeat spirometry and only mild reduction in DLCO. She continued to improve with complete symptomatic resolution at four weeks and near resolution radiographically at 12 weeks. DISCUSSION: Drug induced interstitial pneumonitis is a disease of exclusion. With extensive negative evaluation, close temporal association between initiation of drug and her symptoms and rapid improvement with prednisone and cessation of the drug, it is likely that patient had drug induced interstitial disease secondary to initiation of galcanezumab. CONCLUSIONS: Animal models support this possibility by showing decreased CGRP levels in pulmonary tissue exposed to crystalline silica and crocidolite, both known causes of interstitial lung disease. As such, it is plausible that CGRP plays a role within interstitial pulmonary disease and may have been an unintended target in this case. Given these findings, we determined galcanezumab to be the etiology of her interstitial pneumonitis, which would be the first reported case in the literature. Reference #1: Morimoto Y, Ogami A, Nagatomo H, et al. Calcitonin gene-related peptide (CGRP) as hazard marker for lung injury induced by dusts. Inhal Toxicol. 2007;19(3):283-289. doi:10.1080/08958370601069364 DISCLOSURES: No relevant relationships by Tyler Church, source=Admin input No relevant relationships by Arthur Holtzclaw, source=Admin input No relevant relationships by Donovan Mabe, source=Web Response