Until now, only one other study, which included 14 patients with CTD-ILD, has reported the utility of TBLC for CTD-specific ILD [29]. That study concluded that TBLC can add extra diagnostic value by effectively identifying specific types of histology for patients with CTD-ILD [29]. In contrast, we investigated 31 cases of CTD-ILD histologically confirmed by TBLC and also determined whether adding histological information is useful in developing a therapeutic decision-making strategy. The findings of the present study have important implications.
First, in the case of TBLC-proven pathological UIP in patients with CTD, some patients also have prominent inflammatory cells in addition to a framework of UIP. Pulmonary function of these patients improved with anti-inflammatory agents because lymphocyte aggregation in the interstitium and lymphoid follicles with germinal centers are more frequently observed in CTD-UIP than in IPF [5]. Moreover, in some CTD-ILD cases, it is difficult to classify imaging findings by HRCT as UIP or NSIP, and, in fact, a certain number of patients in the present study were classified as having mixed NSIP/UIP. These features (i.e., UIP with prominent inflammatory cells, mixed NSIP/UIP) may be associated with a better response to anti-inflammatory agents. Therefore, TBLC may be useful when it is difficult to judge which should be prioritized, anti-inflammatory or anti-fibrotic agents.
Second, pathological evaluation using a TBLC-based UIP score may be useful as a predictor of PF-ILD. Cases of UIP showing a combination of patchy fibrosis and fibroblastic foci, with or without honeycombing, were assigned a rating of high confidence in the UIP diagnosis [8]. A pattern of UIP develops in a substantial subset of patients with other non-idiopathic pulmonary fibrotic ILDs and may be associated with higher risk of PF-ILD compared with other fibrotic morphological patterns. Knowledge of an underlying baseline UIP pattern can help to identify a higher likelihood of progression in patients with worsening symptoms or radiological findings [30] because the later phase of fibrogenesis, which is thought to be shared by all conditions with any etiology such as CTD, leads to lung tissue remodeling and subpleural fibrotic lesions as UIP [31]. The INBUILD study showed the effectiveness of nintedanib as an anti-fibrotic agent on PF-ILD other than IPF. That study included a range of fibrosing ILDs, incorporating 170 patients with CTD-ILD, including RA-ILD, SSc-ILD, and MCTD-ILD [8]. In the present study, 6 (40%) of the 15 patients with a TBLC-based UIP score ≥ 1 showed a progressive disease course during the follow-up period, and 4 of them received anti-fibrotic agents (Table 3). If a patient has a TBLC-based UIP score ≥ 1, we speculate that this finding (such as having a UIP-like lesion or not) can lead to considering early intervention with an anti-fibrotic agent as long-term treatment. As mentioned in the previous paragraph, although patients with inflammatory cells in a framework of UIP may potentially respond to anti-inflammatory agents in the short term, they face the possibility of a progressive disease course in the long run. Taken together, although we definitively addressed this, additional information from TBLC may be beneficial when considering early intervention with anti-fibrotic agents in patients with a UIP-based score.
Third, most (5/6) of the patients with NSIP + OP on HRCT were also consistently proven pathologically to have NSIP + OP. Because anti-inflammatory agents are the primary treatment for NSIP + OP [5], when NSIP + OP is present on HRCT, low priority should be placed on performing TBLC. However, because of frequent recurrence and/or refractoriness to anti-inflammatory agents, some patients progress to pulmonary fibrosis over their disease course despite initial improvement [5]. Therefore, if the process is still ongoing, TBLC may be useful only when it is difficult to judge which is the dominant condition during the middle of anti-inflammatory treatment: inflammation or fibrosis.
As adverse events, bleeding and pneumothorax are the most common complications of TBLC [9, 10, 22]. In our study, no patients with severe or serious bleeding or serious pneumothorax were identified. However, previously published data on moderate or severe bleeding varied widely from 1.7 to 15.7%, and that on pneumothorax requiring drainage ranged from 0.9 to 15.5% [22]. As reported by Wu et al. [29], we also placed an endobronchial balloon for bronchial blockage as a routine procedure in our patients, and our cohort included only those with mild (not severe) disease, which might have led to a low rate of, and milder, complications. Importantly, attention must be paid to the quality and quantity of the pathological specimen, which could not be sufficiently proven in TBLC samples of 5 patients in the present study. In fact, one patient with a UIP score of 3 had a long-term stable course, whereas another with a UIP score of 0 had a progressive course. In other words, these patients had clinical courses contradictory to those indicated by their TBLC-UIP scores. When TBLC specimens are inadequate, clinicians should not place too much emphasis on pathological findings in the therapeutic assessment of CTD-ILD.
Our study has several limitations. First, it is a single-institution, retrospective study with a small sample size. Second, there is selection bias because only those patients who could undergo TBLC were included as a pulmonologist determined the necessity for the procedure and enrollment into the study. Third, because the protocol for ILD diagnosis is not standardized in our hospital, clinical practice varies between different clinicians, such as pulmonologists and rheumatologists. Therefore, these data may mask potential differences in care. Fourth, expert thoracic radiologists should analyze HRCT findings, not pulmonologists. Although it is common for pulmonologists to perform HRCT analysis in clinical practice, whether analysis by thoracic radiologists is preferable will require further study. Fifth, a comparable analysis could not be performed in the present study. However, we believe that judgement of whether a patient has UIP-like lesions is meaningful when determining a strategy for treatment because clinicians should consider the possibility that patients will develop progressive ILD in the long run if they have UIP-like lesions at the time of diagnosis [5, 8, 25]. Although the present study is descriptive and no statistical analysis was performed, we believe that it provides useful information on TBLC in patients with CTD-ILD.