The thoracic cage becomes flattened in the progression of pleuroparenchymal fibroelastosis

To the Editor: Pleuroparenchymal fibroelastosis (PPFE) was first reported by Frankel et al. [1]. PPFE can occur without any aetiology or underlying diseases (idiopathic PPFE), or with underlying diseases or conditions. Idiopathic PPFE has been listed as one of the rare idiopathic interstitial pneumonias (IIPs) in the revised international multidisciplinary consensus classification of IIPs [2]. The natural history of PPFE is variable, some are slowly progressive and others sometimes show rapid deterioration resulting in poor prognosis, like idiopathic pulmonary fibrosis (IPF). Idiopathic pulmonary upper lobe fibrosis (PULF), first proposed by Amitani et al. [3], is currently considered to be almost identical to idiopathic PPFE [1, 4, 5], which is now globally accepted as a representative nomenclature for this disorder. Therefore, we use the term PPFE to describe the same disease as PULF. Amitani et al. [3] recognised a characteristic constitution in patients with PPFE: they are slender and their thoracic cage is flattened, i.e. the ratio of the anteroposterior diameter of the thoracic cage (APDT) to the transverse diameter of the thoracic cage (TDT) is abnormally lower than in normal populations. Herein, we have provisionally named this deformity of the thoracic cage as “flat chest”. Other investigators have also noticed this deformity in idiopathic PPFE [6–8]. Flat chest may result from a congenital disposition or …