ABSTRACT NUMBER: ESOC2026A1146 YOUNG-ONSET POSTERIOR CIRCULATION STROKE ASSOCIATED WITH THYROTOXICOSIS AND THYMIC HYPERPLASIA, MIMICKING MYASTHENIA GRAVIS

Abstract Background and aims Stroke in young adults prompts evaluation for non-traditional and systemic causes. Thyrotoxicosis has been associated with cerebrovascular events through prothrombotic, vasospastic, and autoimmune mechanisms, but remains an under-recognised contributor in clinical practice. Methods A 33-year-old male presented with a one-week history of severe left-sided headache, dysphagia, dizziness, nausea, and vomiting, worsened on lying flat, accompanied by left-sided ptosis and hoarse voice. The combination of bulbar symptoms and ptosis initially raised concern for a neuromuscular junction disorder. Neurological examination demonstrated intact limb power and tone with prominent cranial nerve involvement, without focal limb weakness. Initial CT of the brain showed no acute haemorrhage or infarction. MRI subsequently demonstrated acute infarcts involving the left cerebellar hemisphere and left cerebral hemisphere, consistent with posterior circulation stroke. Vascular imaging identified abnormalities of the left vertebral artery, raising suspicion of chronic occlusion with a possible dissection flap. Thyroid function tests revealed markedly elevated free triiodothyronine and thyroxine with suppressed thyroid-stimulating hormone. Thyroid ultrasound demonstrated features consistent with thyroiditis, and computed tomography of the neck revealed thymic hyperplasia. Results The patient was treated with dual antiplatelet therapy for secondary stroke prevention, beta-blockade, and antithyroid medication. He received multidisciplinary input from ENT, endocrinology, SALT, physiotherapy, and occupational therapy. He achieved good functional recovery, mobilising independently at discharge, with residual poststroke fatigue requiring ongoing community rehabilitation. Conclusions This case highlights the diagnostic challenge of posterior circulation stroke mimicking neuromuscular disease and emphasises the importance of considering thyroid dysfunction as a potentially modifiable contributor in young-onset stroke. Conflict of interest Nothing to disclose