Case report

A 54-year-old man developed strikingly asymmetric facial flushing. After returning from cycling outdoors, his wife had remarked that his face appeared strange. He saw in the mirror that the right side of his face was flushed from the exercise, but the left was pale, with a sharp vertical midline demarcation (figure 1). This is characteristic of the Harlequin sign. In the preceding 2 months, he had experienced a new left-sided headache associated with intermittent blurred vision in his left eye.

On examination, there was hemifacial discolouration and left facial anhidrosis. Ophthalmology assessment identified a subtle left ptosis and miosis, with pupil sizes of 3.5 mm (right) and 3.1 mm (left) (Plusoptix Vision Screener).

He underwent urgent investigation for Horner’s …