A case of central Horner syndrome after haemorrhagic stroke

A 75‐year‐old man presented with right hemiparesis secondary to a left thalamic haemorrhage. Five days after presentation, he developed left Horner syndrome. He had left ptosis (Figure, A) with palpebral aperture measured at 3 mm on the left (7 mm on the right). In a well lit room, the left pupil measured 2 mm, while in a dark room, it was 3 mm, confirming miosis. Relative afferent pupillary defect was absent. Left‐sided anhidrosis was also present. A magnetic resonance imaging scan revealed extension of the haemorrhage into the thalamo‐mesencephalic junction (Figure, B–D).

Horner syndrome is caused by disruption to the three‐neuron sympathetic pathway. The first order neuron begins in the hypothalamus and synapses at the cervical cord. The second order neuron travels through the brachial plexus and over the lung apex to synapse in the superior cervical ganglion. The third order neuron ascends with the carotid artery to the iris dilator and Muller muscle.

Clinically, third order Horner can be differentiated by lack of anhidrosis and response to hydroxyamphetamine.1 This is due to the sparing of sudomotor fibres that branch off at the superior cervical ganglion and the lack of noradrenaline release from the postganglionic neuron respectively.