Giant Cell Arteritis/Polymyalgia Rheumatica and Atypical Pulmonary Carcinoid Tumor: A Paraneoplastic Syndrome?

BACKGROUND Giant cell arteritis (GCA) is the most common large-vessel vasculitis in individuals over age 50 years. Although it typically affects extracranial branches of the carotid artery, central nervous system involvement is rare and can manifest with ischemic stroke. Links between GCA and malignancy have been reported, especially hematologic cancers, but paraneoplastic GCA associated with solid tumors remains exceptional and poorly understood. CASE REPORT We describe a 59-year-old man presenting with temporal headaches, right-hand paresthesia, monocular visual loss, and gait instability. Imaging revealed left thalamic ischemia and bilateral vertebral artery stenosis without atherosclerosis. Examination and Doppler ultrasound supported a diagnosis of GCA with associated polymyalgia rheumatica (PMR), although a temporal artery biopsy was negative. Inflammatory markers were only moderately elevated, consistent with reports of GCA cases with ischemic complications. PET-CT incidentally identified a mediastinal mass, confirmed as small-cell pulmonary neuroendocrine carcinoma. Symptoms improved with corticosteroids, but tapering below 15 mg/day caused relapse, requiring methotrexate. Despite partial oncologic response, brain metastases appeared 8 months later. Follow-up vascular imaging showed regression of arterial stenoses under corticosteroids, arguing against atherosclerosis and supporting the inflammatory nature of the lesions. GCA manifestations remained corticosteroid-dependent throughout follow-up. CONCLUSIONS The simultaneity of GCA and lung neuroendocrine carcinoma, persistence of corticosteroid dependence, and lack of remission despite oncologic response strongly suggest a paraneoplastic mechanism. This case emphasizes the need for heightened suspicion of underlying cancer in patients with atypical, biopsy-negative, or treatment-resistant vasculitis. Recognition of paraneoplastic GCA may improve early cancer detection and influence management decisions at the intersection of rheumatology and oncology.