Partial Horner's Syndrome as a Manifestation of Carotid Artery Dissection: A Case Report and Diagnostic Approach.

Horner's syndrome is a neurological condition resulting from a disruption in the sympathetic pathways supplying the head and neck. This syndrome often occurs secondary to various aetiologies, including trauma, neoplastic compression, or vascular pathology such as carotid artery dissection. Although the clinical presentation is well-defined, Horner's syndrome remains relatively rare, and there are limited established management guidelines. Of particular concern is the acute onset of occipital pain in association with partial Horner's syndrome, as it raises the suspicion of cervical artery dissection, a potentially life-threatening condition. Prompt diagnosis using MRI angiography or CT angiography of the neck is critical, as routine CT head imaging may not be sufficient to identify the underlying pathology. We present a case of a 44-year-old female who presented with left-sided occipital headache, neck pain, and anisocoria, which led us to believe this was a manifestation of Horner's syndrome. The patient was treated with dual antiplatelet therapy, resulting in complete resolution of the dissection on follow-up imaging. This case underscores the importance of considering carotid artery dissection (CAD) in the differential diagnosis of Horner's syndrome, particularly in the absence of trauma. It highlights the need for urgent neuroimaging and a multidisciplinary approach to diagnosis and treatment to improve patient outcomes and prevent life-threatening sequelae.