Idiopathic Hypertrophic Pachymeningitis with Elevated Anti-Thyroglobulin Antibodies—A Case Report

<b>Background and clinical significance</b>: Idiopathic hypertrophic pachymeningitis (IHPM) is a rare inflammatory disorder characterized by diffuse or focal dural thickening and heterogeneous presentations. We report a corticosteroid-responsive IHPM with elevated anti-thyroglobulin (anti-Tg) antibodies despite oncologic control after thyroidectomy. This case suggests that systematic assessment for autoimmunity should be a standard component of the IHPM work-up. <b>Case presentation</b>: A 77-year-old woman presented with recurrent vertigo, imbalance, and headaches. Brain MRI showed diffuse pachymeningeal thickening with mild heterogeneous enhancement, radiologically stable over >2 years. Extensive evaluation excluded infectious, neoplastic (including paraneoplastic), cerebrospinal fluid hypotension and systemic autoimmune causes; findings did not support IgG4-related disease. Thyroid work-up revealed hypothyroidism with multinodular goiter; total thyroidectomy was performed, and there was no indication for adjuvant radioiodine therapy. Despite oncologic control, anti-Tg antibodies remained markedly elevated, while anti-thyroid peroxidase antibodies (anti-TPO) declined. Symptoms repeatedly improved with oral methylprednisolone and recurred on taper; adverse effects were mild and manageable. The patient remains under clinical and oncologic surveillance with symptom-guided steroid re-challenge. <b>Conclusions</b>: IHPM may exhibit a dissociation between clinical response and radiologic course. Persistently elevated anti-Tg after thyroidectomy can coexist with IHPM and may signal ongoing autoimmunity rather than active cancer.