Chronic hypersensitivity pneumonitis (CHP) is a prominent aetiology of diffuse parenchymal lung disease (DPLD), contributing to over 47% of the inclusions in the ILD-India registry. The diagnosis of CHP is difficult because the pathological description needs lung biopsy that remains mostly undone. The high-resolution computed tomography (HRCT) chest, however, can give some definite clues for the possibility. In our series, the HRCT diagnosis of HP was done by a pulmonologist and a radiologist on an agreement for the probability of HP in their independent interpretation of HRCT chest pictures. The radiologically possible-HP diagnosis was supported by positive IgG precipitin titre for avian antigen by immunoCAP method. A precipitin titre value >30 mg mgA/L was taken as significant. The clinico-radio-serological positivity was further supported by history of exposure to pigeons/birds to build up a nearly definite avian antigen–induced diagnosis of CHP. However, the possible CHP cases from other causes could not be evaluated serologically as the panel with common antigens was not available to us at that point of time.
The study did not essentially include subjects with features of CHP without any etiological confirmation and exclude other causes like connective tissue disease associated-interstitial lung disease (CTD-ILD) and sarcoidosis. The latter was done by a thorough clinical exercise (noting the American Rheumatology Association [ARA]) criteria for the common CTDs supported by the relevant serological tests whenever possible in the real-world situation. Sarcoidosis was diagnosed with demonstration of non-ceasing granuloma with exclusion of tuberculosis. All the patients underwent Doppler echo-cardiography by a single dedicated non-invasive cardiologist who looked systematically for evidence of pulmonary hypertension (PH) in addition to other parameters. Furthermore, we looked for the presence of clinical and radiological XRay -posterio-anterior (PA) view (chest X-ray [PA view] and HRCT) features of PH to satisfy the clinico-radio-echocardiographic screening criteria of the institute for the presence of PH.
We had 95 cases of suspected HP included in the evaluation from 2018 to 2019. These patients were sub-divided into two groups - CHP caused due to exposure to avian antigen and CHP likely from other possible etiologies. The above two groups were thus compared on the basis of demographic, spirometric, functional health status and echo-cardiographic variables [Table 1].
The results reflect that the two groups were similar on demographical and spirometric lung function variables, but the patients with CHP from avian antigen had significantly higher systolic pulmonary artery pressure (PAP). To appreciate the relative contribution of the variables for the difference between the two groups, we used the VIP plot that suggested the presence of PAP as the most effective discriminant between the two groups [Figure 1a]. However, the overlap between the clusters was very high, suggesting limited applicability of the information [Figure 1b]. In one of our previous observations, we found a very high frequency HRCT-chest that suggested PH in CHP patients induced by chronic exposure to avian antigen. Such exposure of avian antigen has been found to be one of the common causes of CHP. Avian exposure was present in 21.4% of 513 HP patients in the ILD-India registry, with the adjusted odds ratio of 3.52 (P < 0.001) for developing HP after exposure. Pulmonary hypertension is found quite frequently in CHP and is associated with poor survival prospect. The subjects having CHP with history of exposure to avian antigen had a lesser but statistically insignificant mean duration of illness compared to the other group. The standard deviation in both the groups was very wide for the illness duration, making it unsuitable for interpretation through VIP plot [Figure 2]. Despite the weakness of having no biopsy-proven diagnosis of HP, a non-stringent exclusion of other aetiologies, non-inclusion of treatment history, and dearth of haemodynamic confirmation by right heart catheterisation, our observation demands attention. Furthermore, objective validation of our observation is, thus, warranted.
Financial support and sponsorship
The research was funded by the organization itself.
Conflicts of interest
There are no conflicts of interest.
We are thankful to the technicians and staff members of the institute who supported us in accomplishing the job.
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