Background Interstitial lung disease serves as an umbrella term to cover over 100 conditions causing scarring and inflammation of the lungs. Common offending agents include autoimmune disease such as lupus and rheumatoid arthritis, pneumoconiosis such as asbestosis, hypersensitivity pneumonitis, or adverse reactions to medications. Nitrofurantoin is one such medication that can cause pulmonary injury, with about 1 in 5000 having acute hypersensitivity presenting an average of 9 days after initiation, while chronic pneumonitis reactions take 6 months to several years. Risk factors include age over 60, pre-existing lung conditions and renal impairment. Commonly used to treat uncomplicated lower urinary tract infections, we present the case of a patient that is unique for developing lung toxicity while on this medication outside of the expected timeframe of this manifestation.

Case Presentation An 86-year-old female with past medical history significant for hypertension, hypothyroidism, CKD stage 2, presented to the emergency department with exertional dyspnea and fatigue for 3 weeks. For 4 months leading up to this admission, the patient had been on daily UTI prophylaxis with nitrofurantoin. She is a former smoker with a 50-pack year and quit 3 years ago. Pertinent labs include positive ANA, RF and anti-CCRP antibodies. 2D Echo was unremarkable. CT chest was significant for diffuse dense ground glass opacities with scattered areas of consolidation worse at the peripheries. There was no evidence of honeycombing, traction bronchiectasis or pleural effusion. Pulmonology was consulted and a bronchoscopy was performed. BAL studies were negative for Aspergillus, PCP, Histoplasma, Blastomyces. The clinical history, CT imaging findings and further workup results were suggestive of nitrofurantoin lung toxicity. Nitrofurantoin was discontinued and patient was started on steroid taper of oral prednisone, 2L/min O2 supplementation to maintain SPO2>90% with plan for repeat CT chest in 6 weeks.

Discussion As the 5-year survival rate for ILD is 48.1%, identifying the cause is key for overall prognosis. In our patient with infectious and cardiogenic causes ruled out, autoimmune work up was positive. It’s not unusual to have positive antibodies in nitrofurantoin toxicity, including RF and ANA having been reported. It would be unusual to develop acute RA- related lung disease at her age without any other systemic symptoms or signs. Improved function and imaging on repeat follow-up will confirm, with this case serving to illustrate the high index of clinical suspicion needed by the provider to implement timely interventions in cases that present in an atypical fashion.