We recently examined a 77-year-old woman with Horner syndrome and ipsilateral abduction deficit that we attribute to giant cell arteritis (GCA). This combination of findings has not been previously reported in GCA. She had a history of hypertension, hyperlipidemia, atrial fibrillation, congestive heart failure, and colon carcinoma. Six weeks before presentation, she developed bitemporal headaches. She had stopped eating solids as a result of jaw claudication and had lost weight. She had diffuse myalgia and was unable to sleep well because of bilateral scalp tenderness. She noticed binocular horizontal double vision that was worse on left gaze and had experienced numerous episodes of blurring of vision in both eyes. Her family noted drooping of her left upper lid. Neuro-ophthalmic examination revealed a best-corrected visual acuity of 20/40 in both eyes consistent with cataracts. Visual fields and color vision were normal. Left upper lid ptosis of 2 mm was present. In dim light, the right pupil measured 5.5 mm and the left 3.5 mm. In bright light, the right pupil measured 4.5 mm and the left 3 mm. Both pupils reacted briskly to light without afferent defect. Horner syndrome was confirmed by instilling 10% cocaine into both eyes (Fig. 1). (Hydroxyamphetamine was not instilled as a result of its unavailability.) Ocular ductions were full except for reduced abduction of the left eye. There was a 12 prism-diopter esotropia in primary position increasing to 20 on left gaze. The fundus examination was normal.FIG. 1: Left Horner syndrome. After instillation of one drop of a 10% cocaine solution, the right pupil has become dilated and the left pupil has remained small. Left upper lid ptosis is evident.Temporal arterial pulsation was absent and the scalp was tender, but there was no thickening or nodularity. Westergren erythrocyte sedimentation rate (ESR) was 57, C-reactive protein was 4.1, and platelet count was 475,000. MRI of the brain with contrast was normal and magnetic resonance angiography showed an incidental small basilar tip aneurysm. We made a diagnosis of GCA with concurrent Horner syndrome and left lateral rectus paresis. Intravenous methylprednisolone at a dosage of 250 mg per day and 80 mg oral prednisone per day was initiated. She was also started on alendronate, calcium with vitamin D, and ranitidine. Temporal artery biopsy on the left side was consistent with giant cell arteritis (Fig. 2).FIG. 2: Temporal artery biopsy shows inflammatory cells in the vessel wall. Inset shows giant cells (arrows).Within a week of initiation of treatment, she had resolution of diplopia, headaches, and temporal scalp pain. Ptosis and pupillary abnormality remained unchanged. ESR, C-reactive protein, and platelet counts normalized in a week. Prednisone was tapered slowly over 18 months. Horner syndrome resulting from GCA is very rare. Three cases of GCA and Horner syndrome have been reported in the English literature (1-3). Bell et al (1) reported a patient with GCA and Horner syndrome resulting from a brainstem stroke. Askari et al (2) reported a patient with internuclear ophthalmoplegia and Horner syndrome resulting from presumed giant cell arteritis. Bromfield and Slakter (3) reported a patient with GCA with postganglionic Horner syndrome. To our knowledge, no one has reported the combination of Horner syndrome and ipsilateral abduction deficit in GCA. We were unable to perform the hydroxyamphetamine test to confirm the location of the lesion. The absence of brainstem and spinal cord signs and a normal brain MRI argue against a preganglionic location. Hollenhorst et al (4) suggested that paresis of different extraocular muscles at different times is the result of ischemia of the muscles or the nerve and not a brainstem lesion. Barricks et al (5) found extraocular muscle ischemia at autopsy in a patient with bilateral ophthalmoplegia resulting from GCA. Sibony and Lessell (6) reported aberrant regeneration in a patient with pupil-sparing third cranial nerve palsy resulting from GCA and suggested that ophthalmoplegia is neurogenic rather than myogenic. Meadows (7) suggested ischemia of vasa nervorum, whereas Martin (8) suggested ischemia of the extraocular muscles as the likely cause of diplopia in GCA. In our patient, the combination of Horner syndrome and an ipsilateral abduction deficit suggests a cavernous sinus lesion. Within the cavernous sinus, the postganglionic sympathetic fibers travel with the sixth cranial nerve lateral to the internal carotid artery. Bromfield and Slakter (3) proposed that granulomatous inflammation of the internal carotid artery might directly involve the sympathetic fibers. We believe that the sixth cranial nerve in our patient could have been similarly affected. Guruswami Arunagiri, MD Shanmugam Santhi, MD Thomas Harrington, MD Departments of Ophthalmology and Rheumatology, Geisinger Medical Center, Danville, PA