A 65-year-old Japanese man presented with right pleural effusion during follow-up after percutaneous coronary intervention for angina pectoris. He was asymptomatic. Smoking history was 50 cigarettes/day for 30 years. No allergic history or family history of tuberculosis infection was elicited. The patient was employed in clerical work, with no exposure to asbestos.
On physical examination, temperature was 36.4  C, blood pressure was 117/65 mmHg, pulse rate was 54 beats/min, respiratory rate was 18 breaths/min, and peripheral oxygen saturation was 98% in ambient air. Lung sounds on auscultation were diminished in the lower right lung field. No articular findings, rash, or swelling of the salivary or lacrimal glands were identified. According to the laboratory data, C-reactive protein (CRP) was 1.08 mg/dl, IgG was 2183 mg/dl, IgG4 was 299 mg/dl, soluble interleukin-2 receptor was 956 U/ml, and negative results were obtained for various autoantibodies, tumor markers, and the interferon-gamma release test (QuantiFERON TB; QIAGEN, Hilden, Germany) (Table 1).
Chest X-ray showed right pleural effusion (Fig. 1A). Contrast-enhanced chest CT showed right pleural thickening, pleural effusion, mediastinal lymph node enlargement, periaortitis of the abdomen and perivertebritis (Fig. 2). FDG-PET-CT showed that maximum standardized uptake value (SUVmax) at these sites was 4-6. SUVmax was 2.17 at the pleura (Fig. 3). Echocardiography revealed left and right atrial dilation, estimated right ventricular pressure was 36.7 mmHg, although ejection fraction was good, and no valvular disease or synergy was evident. Thoracentesis showed a brownish, lymphocyte-predominant pleural exudate with high levels of ADA, IgG, and IgG4 (Table 2).
Smears, cultures and polymerase chain reaction (PCR) tests for tuberculosis and Mycobacterium avium complex all yielded negative results. Cytology was defined as Class II with lymphocytes and plasma cells predominating (Table 2). On thoracoscopy under local anesthesia, thoracoscopic findings revealed no pleural adhesion. Parietal pleura showed white and dense granular lesions (Fig. 4A). Pleural thickness showed mild and white with partly hypervascularization and redness in the cupula and lateral (Fig. 4A). Using narrow-band imaging, distention of capillaries were revealed among dense granular lesions (Fig. 4B). Visceral pleura showed no abnormalities. We obtained these granular lesions in the lateral. These findings were referred to the standardized description of thoracoscopic findings in Japan. Pleural biopsy specimens showed infiltration of inflammatory cells with tiny lymphocytes and fibrosis. The ratio of IgG4-to IgG-positive plasma cells (IgG4/IgG) was 22.4%, and 10 IgG4-positive cells were seen on a high-power field (HPF) (Fig. 5A). Transbronchial needle aspiration of a subcarinal lymph node on endobronchial ultrasonic bronchoscopy showed inflammatory cell infiltration with both small and large lymphocytes, and some plasma cells. IgG4/IgG could not be evaluated (Fig. 5B). A cell block of pleural effusion suggested that IgG4/IgG was about 50% (Fig. 5C). No obliterative phlebitis or storiform fibrosis was identified. No granulomas or acid-fast bacteria were evident from any biopsy specimens. According to the comprehensive diagnostic criteria for IgG4-RD proposed in 2001, this case would be classed as "possible IgG4-RD". On the other hand, this case did not meet the diagnostic criteria for definitive IgG4-RRD. Since no findings specific for tuberculosis or rheumatoid arthritis were identified, we clinically diagnosed IgG4-RD with pleural effusion.
After we initiated PSL at 40 mg/day (0.6 mg/kg/day), pleural effusion was improved. The dose of PSL was gradually tapered every 2 weeks. As of the time of writing, we are continuing to administer PSL at 2.5 mg/day with no apparent recurrence (Fig. 1B). This responsiveness to PSL supported the diagnosis of IgG4-RD. Based on the 2019 classification criteria for IgG4-RD in the United States, this case met the inclusion criteria, and did not meet any exclusion criteria. Total score for inclusion was 35 points, over the 20 needed for diagnosis of IgG4-RD. We finally diagnosed IgG4-RD with pleural effusion.
18F-fluorodeoxyglucose PET-CT showed that mediastinal lymph node, periaortic, and prevertebral maximum standardized uptake value (SUVmax) was 4-6. SUVmax was 2.17 at the pleura.