IgG4-related lung disease with recurrent pulmonary lesions during steroid therapy and difficulty in differentiating from malignancy: a case report oleh Tomohito Okubo, Nariyasu Nakashima, Yoshimasa Tokunaga, Nobuyuki Kita, Hiroyuki Nakamura, Ryou Ishikawa, Setsuo Okada, Tetsuhiko Go, Hiroyasu Yokomise