A 56-year-old male presented with a long-standing history of episodic headaches that had been worsening over the past few months. The headache episodes were characterized by sharp, stabbing pains localized around the left eye, often accompanied by nausea, vomiting, photophobia, and phonophobia. These headache attacks lasted several hours and were notably associated with autonomic features, including left-sided facial flushing. The photographs taken during these episodes showed left facial flushing, right eyelid ptosis, and right-sided miosis. The patient reported that facial flushing would resolve after headache episodes ceased. 
At the time of clinical presentation, the only neurological findings were mild left eye ptosis and miosis. An extensive diagnostic workup, including an MRI of the brain, cervical, thoracic, and lumbar spine; CT angiography (CTA) of the head and neck; and a CT maxillofacial scan, was unremarkable. The patient had previously tried various prophylactic treatments such as valproic acid, nortriptyline, and verapamil without symptomatic relief. The patient was diagnosed with idiopathic left Horner’s syndrome, and his migraines, accompanied by autonomic dysfunction, manifested with unilateral flushing opposite the site of Horner’s, presenting as Harlequin syndrome.