Mediastinal and hilar lymphadenopathy is observed very frequently (Fig. 19.5) [6, 8]. With regard to pleural lesions, some cases have shown pleural nodular lesions in the visceral or parietal pleura [5]. Although pleural effusion is a comparatively rare feature [9, 11], pleuritis with fibrinous exudates and reactive changes are often observed in the histological findings from surgical lung biopsy specimens in patients with intrathoracic IgG4-related disease [18].

Other findings that should be noted include soft tissue mass in the paravertebral region, which may be suggestive of mediastinal fibrosis (Fig. 19.6) [7, 19, 20].

Bronchial asthma (BA) is sometimes associated with AIP (7–10 %) [13, 14, 21, 22]. A specific antigen for asthma is not known [14]. Steroid treatment is effective for both BA and AIP. However, after tapering of the steroid, BA often becomes aggravated despite no change in the pancreas, which hinders cessation of the steroid [13]. Although BA is not included in IgG4-related pulmonary disease in general, history of BA should be noted in AIP patients.

Apart from BA, in which airway stenosis is reversible, central airway stenotic disease associated with AIP has been reported by Ito et al. [12]. In the patient in that case, bronchoscopic examination revealed an irregular tracheobronchial stenosis accompanied by an edematous mucosa and engorged vessels. Bronchial biopsy specimens demonstrated diffuse infiltrations of IgG4-positive plasma cells, lymphocytes, and eosinophils with fibrosis. CT showed marked thickness of the bronchovascular bundle. These lesions improved after steroid treatment. Thus, it should be noted that IgG4-related lesions may occur in any part of the respiratory system.

Histopathological findings associated with intrathoracic IgG4-related disease resemble those seen in extrapancreatic lesions, with some exceptions. That is, lymphoplasmacytic inflammation, fibrosis, phlebitis, and increased numbers of IgG4-positive plasma cells are characteristic of intrathoracic IgG4-related disease [4, 7, 11, 18, 23, 24].

Compared with the histopathological findings observed in the pancreas of AIP patients, storiform fibrosis is not as apparent in the lung, where collagenous fibrosis and active fibroblastic proliferation are more prominent [18]. Moreover, in the lung, arteries as well as veins often show intimal and mural inflammation, in contrast to the findings for an affected pancreas, which shows obliterative phlebitis with sparing of the arteries [18, 25].

Intrathoracic lesions associated with IgG4-related disease generally respond to steroid treatment [1–7, 10–12, 18, 20, 25–27]. The exact steroid regimens have not been specified in many of the studies to date but typically consist of oral prednisolone beginning at a dose of 30–60 mg/day. Favorable response is usually observed within 2 weeks from the start of treatment. Then, the prednisolone dose is gradually tapered to a maintenance dose of 5–10 mg/day. The optimal dose and duration of steroid treatment remain undetermined. Steroid treatment for the indication of asymptomatic intrathoracic lesions is also problematic. The question arises as to whether or not it is necessary to increase the dose of prednisolone when asymptomatic lung lesions appear during maintenance steroid treatment for AIP. As far as we know, many Japanese chest physicians are not inclined to treat asymptomatic intrathoracic lesions with steroids. This is probably because for some pulmonary lesions, improvement may only be assessed by observation, at least from a short-term viewpoint [7, 28, 29]. However, the long-term prognosis of such patients is unknown. Moreover, there has been no report on the long-term prognosis of intrathoracic lesions treated with steroids. In addition, many problems remain to be solved in establishing the optimal treatment policy.

Despite good response to steroid treatment, steroid treatment for pulmonary nodular lesions without pathological diagnosis is undesirable. It is often very difficult to differentiate IgG4-related pulmonary nodular lesions from lung cancer [4]. Moreover, at our institute and affiliated hospitals, 5 cases of lung cancer have been found during follow-up of 113 patients with AIP. There were 15 malignancies, but lung cancer was observed most frequently [30]. Thus, surgical resection should be considered when differential diagnosis is difficult.

Concerning nodular lesions, the effectiveness of steroid treatment for large nodular lesions may not always be determined because many have been resected. Ito et al. reported a case in which IgG4-related pulmonary nodular lesions showed no response to steroid treatment [13]. In our experience (Fig. 19.1), nodular lesions became a little smaller but did not disappear. It should be noted that all intrathoracic lesions do not improve dramatically after steroid treatment.