A43-03 “Identical” But Different; Twin Brothers With Different Presentations of Familial Pulmonary Fibrosis

Introduction Familial Pulmonary Fibrosis is a subset of interstitial lung disease characterized by two or more first degree relatives with pulmonary fibrosis. Our cases demonstrate identical twin siblings who displayed different clinical trajectories and CT patterns of pulmonary fibrosis. Case Patient 1 is a 72-year-old male who presented to clinic with 6 months of worsening exertional dyspnea. His pulmonary function test showed a restrictive pattern with FVC 67%, FEV1 66%, TLC 67% and DLCO 53% predicted. A non-contrast chest CT showed sub-pleural reticulations, minimal ground glass opacities, and mild traction bronchiectasis (Figure 1a). The pattern was deemed most compatible with probable UIP. Initial laboratory work-up consisted of unremarkable autoimmune serologies. He denied any history of occupational or environmental exposures but did note a history of Raynaud’s and a brother, Patient 2, with pulmonary disease that had been attributed to scoliosis. After a subsequent CT showed mild progression of fibrosis, he was started on pirfenidone, and we recommended that his brother contact our clinic to be evaluated. Patient 2 was seen in clinic two months later. He is also a 72-year-old male who was experiencing a worsening dyspnea and a pronounced intermittent productive cough. He had previously been diagnosed with bronchiectasis and “mild interstitial lung disease” 7 years prior to his visit. His pulmonary function test showed FVC 68%, FEV1 66%, TLC 67%, and DLCO 44% predicted. This was a significant decline from previous PFTs in 2020. His chest CT was also consistent with probable UIP although his fibrotic pattern was basal predominant with little apical involvement, traction bronchiectasis, honeycombing and marked scoliosis (Figure 1b). His labs also consisted of unremarkable autoimmune serologies, and denied any significant occupational or environmental exposures as well. He was diagnosed with familial pulmonary fibrosis and started on pirfenidone. Patient 1 is currently undergoing genetic testing to further classify their FPF. Discussion The most common pattern of FPF on high resolution CT is a UIP pattern. Despite this it has been noted that even within families there can be a variance in CT findings. This case highlights that variability in a unique way with a significant variance seen in twin siblings that otherwise have identical genetic predispositions and similar environmental exposures. It reinforces the importance of taking a careful family history, as even twin brothers may not know the details of family members’ diagnoses.