Anti-pituitary-specific transcription factor-1 hypophysitis developing after thymoma resection: a case report with review of literature.

Anti-pituitary-specific transcription factor-1 (PIT-1) hypophysitis is an acquired autoimmune disorder characterized by selective deficiencies of growth hormone (GH), prolactin (PRL), and thyrotropin (TSH). It is typically driven by ectopic PIT-1 expression in thymomas or other malignancies, and in previously reported cases, thymectomy has been shown to attenuate autoimmunity. In contrast, we report a novel case that developed after thymectomy. A 42-year-old woman with normal preoperative thyroid function underwent resection of a WHO type B2 thymoma. Eleven months later, she developed specific deficiencies of GH, PRL, and TSH. The diagnosis of anti-PIT-1 hypophysitis was confirmed by the presence of serum anti-PIT-1 antibodies and PIT-1-reactive cytotoxic T lymphocytes. Immunohistochemistry revealed ectopic PIT-1 expression in the resected tumor. Replacement therapy with levothyroxine and recombinant human GH was initiated. Serum FT4 and IGF-1 levels subsequently improved to normal. Two-year post-thymectomy chest computed tomography revealed no tumor recurrence. This unique clinical course challenges the conventional view that the presence of the tumor alone is sufficient to drive autoimmunity. Instead, it suggests a multifactorial pathogenesis requiring the convergence of ectopic antigen expression, genetic predisposition, and a potential trigger. We hypothesize that thymectomy itself acted as the trigger disrupting immune tolerance, potentially through immunogenic cell death or alterations in the immune milieu. This case highlights anti-PIT-1 hypophysitis as a potential post-thymectomy autoimmune complication and that central hypothyroidism should be considered in patients presenting with nonspecific symptoms after thymectomy. Further research is needed to delineate risk factors for susceptibility and to develop preventive strategies.