Horner's Syndrome

This is a rare condition that results from disruption of the ocular sympathetic nerves. They run between the hypothalamus and the eye, and serve the muscles of the upper eyelid and dilator fibres of the iris. The levator palpebrae superioris has sympathetic innervation and so lack of sympathetic tone makes the lid droop.

This is a classical medical description but it is an uncommon finding.

The sympathic nerve supply to the eye passes through 3 neurones:

• The first nerve originates in the posterolateral hypothalamus and descends through the mid brain and pons, to synapse at level C8-T2, the intermediolateral cell column of the spinal cord.
• The second nerve leaves the cord at level T1 and ascends in the sympathetic chain over the apex of the lung to synapse in the superior cervical ganglion at the level of the bifurcation of the carotid (C3-4).
• The third (post-ganglionic) neurone passes alongside the internal carotid artery, sending branches to sweat glands of the face, and passes via the cavernous sinus to enter the eye via the superior orbital fissure. It passes via the long ciliary nerves to supply the iris dilator, the inner fibres of which are the Müller muscle, and the eyelid elevator.

The sympathetic fibres to the eye have a complex course but never cross over. Therefore, Horner's syndrome is a very good lateralising sign but a very poor localising sign to identify the position of the lesion. However, there may be some features that can be used to help determine the level of the lesion¹ and they will be mentioned below.

Characteristic features are:

• Ipsilateral ptosis (drooping of upper eyelid) with possible contralateral retraction of the eyelid.
• Miosis (constriction of pupil).
• Vasodilatation and absence of sweating on the same side of the face.
• There may be increased amplitude of pupillary accommodation.
• There may appear to be mild enophthalmos (retraction of the eye) due to the sagging lid but this is apparent rather than real.

There are some features that may help to determine the level at which the lesion occurs:

• Patients with preganglionic lesions may have facial flushing. This symptom is called the harlequin effect and occurs in some patients as a result of physical exercise.
• Patients with postganglionic lesions may have ipsilateral orbital pain or a headache similar to migraine.
• A lesion in the common carotid artery area causes loss of sweating that involves the entire side of the face.
• Lesions distal to the carotid bifurcation produce lack of sweating that is confined to the medial aspect of the forehead and the side of the nose.

In congenital Horner's syndrome there may be heterochromia of the irides. Pigmentation of the iris is under sympathetic control, but is usually complete by the age of 2, so hypopigmentation of the affected side will not be in apparent when the syndrome develops after this age.

Be sure that this is really Horner's syndrome.

• Simple ptosis may occur with an oculomotor lesion. As the nerve supplies all the external ocular muscles except for superior oblique from IV and lateral rectus from VI, the affected eye is likely to point down and laterally. There may be diplopia and failure of full range of eye movements.
• Senile ptosis is the name sometimes given to simple ptosis in old age.
• Raeder's syndrome, named after a Norwegian ophthalmologist, is a combination of orbital pain, miosis, and ptosis. He called it paratrigeminal syndrome.
  • If there are also lesions of the cranial nerves III, IV, V, VI on the ipsilateral side, suspect a mass lesion in the middle cranial fossa. This is called Raeder's paratrigeminal syndrome, type I.
  • A benign form occurs with episodic retrobulbar or orbital pain, with miosis and ptosis but without associated cranial nerve lesions. It is considered a variant of migraine and is called Raeder's paratrigeminal syndrome, type II.
• The Holmes-Adie syndrome is when one or both pupils are dilated and respond slowly or if at all to light or to accommodation. The patient may complain of sensitivity to light in the affected eye. Loss of knee and ankle jerks may also be present, but there are no other signs of neurological disease. It is usually unilateral and without pathological significance. It is most common in women aged 20 to 40 years.
• The Argyl-Robinson pupil responds slowly, if at all to light but reaction to accommodation is normal. It is a feature of neurosyphilis, usually tabes dorsalis.

Pharmacological testing can help to identify if the lesion is preganglionic or post ganglionic.

• Eyedrops of 2% cocaine will normally cause dilatation of the pupil but there is no response in Horner's syndrome. It inhibits the re-uptake of noradrenaline but this requires an intact sympathetic system. It confirms the diagnosis but does not localise the lesion.
• Hydroxyamphetamine 1% drops (Paredrine) or Pholedrine 5% (n-methyl derivative of hydroxyamphetamine) can be instilled but wait at least 48 hours after performing the cocaine test. The drops force release of endogenous noradrenaline which is absent if the third nerve is damaged. Hence, a first or second nerve lesion will result in dilatation but third (postganglionic) lesions do not dilate.

Further investigations include:

• Chest x-ray is required as apical carcinoma of lung is a common cause.
• CT scan may be useful to identify a stroke.
• MRI angiography may demonstrate dissection of the carotid artery.

Horner's syndrome is a physical sign and not a disease. Therefore, management involves trying to diagnose the underlying condition and treat it, if possible.

Johann Friedrich Horner was a Swiss ophthalmologist who was born in 1831. He started his medical studies in Zurich in 1849 and obtained his doctorate in 1854 with a highly praised thesis on spinal curvature. He investigated the role of retinoscopy in the diagnosis of systemic diseases. He was made Professor of Ophthalmology in Zurich in 1873. He described the syndrome that bears his name in 1869.⁵ In France it it called Bernard-Horner syndrome, adding the name of Claude Bernard. Horner died in Zurich in 1886. There is rather more detail available about his many achievements including the observation that red-green colour blindness is transferred to males through the female line, as is haemophilia.⁶