Neuroanatomy^[1]

• First-order sympathetic fibres originate in the hypothalamus and descend through the brainstem to level C8-T2 of the spinal cord where they synapse on preganglionic sympathetic nerve fibres.
• Second-order fibres leave the cord at level T1 and ascend 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 common carotid artery (C3-C4).
• Third-order (postganglionic) fibres pass alongside the internal carotid artery, sending branches to the blood vessels and sweat glands of the face, and pass via the cavernous sinus to enter the eye via the superior orbital fissure. They pass via the long ciliary nerves to supply the iris dilator and Müller's muscle.

Presentation

Symptoms

• Inability to fully open eye on the affected side.^[2]
• Loss of sweating on the affected side.
• Facial flushing (if preganglionic lesion).
• Orbital pain/headache (if postganglionic lesion).
• There may be other symptoms depending on the underlying cause (see 'Aetiology', below), eg head, neck or facial pain on the affected side if associated with carotid artery dissection.

Signs^[3]

• Constricted pupil on the affected side:
  • Shine a torch in the eye to make the pupil constrict.
  • Remove the torch and watch the pupil dilate.
  • Do the same on the other side and compare the response.
  • The affected pupil lags behind the other in dilation as it lacks sympathetic tone.^[4]
• Ipsilateral dry skin on the face due to loss of sweating:
  • Take both index fingers and place then together in the middle of the forehead. Then run them laterally over the forehead to just lateral to the eyebrows.
  • On the affected side there may be more friction as the skin is drier because there is no sweating on that side.
  • 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 on the medial aspect of the forehead and the side of the nose.
• Ipsilateral partial ptosis (drooping of the upper eyelid) with possible paradoxical contralateral eyelid retraction.
• There may be apparent mild enophthalmos due to the sagging lid.
• There is increased amplitude of accommodation.
• Heterochromia irides may occur with congenital Horner's syndrome.^[5] The iris on the affected side remains blue whilst the other changes to brown. Pigmentation of the iris is under sympathetic control and is usually complete by the age of two years.
• Examine for the presence of lymphadenopathy (see table, below).
• Other signs depend on underlying cause (see table, below).

Aetiology

• Horner's syndrome associated with pain needs investigation. If there is arm, shoulder or hand pain think of Pancoast's syndrome. If pain is in the face or neck, think of carotid dissection. Pain and transient visual loss may be due to carotid dissection.^[2]
• Unless there is a known aetiology such as birth trauma, all children with acquired Horner's syndrome require thorough investigation, as there is frequently serious underlying disease, including neuroblastoma, trauma, rhabdomyosarcoma and brainstem vascular malformation.^[6]
• A rare congenital form of Horner's syndrome is described.^[5] It may present as an autosomal dominant condition or as a spontaneous mutation.
• Preganglionic lesions are less common but more likely to be malignant.

Differential diagnosis

• The differential diagnosis of ptosis is discussed in the separate article Ptosis and Lid Lag.
• Pupillary abnormalities.
• Also consider unilateral use of miotic drugs.

Investigations

Investigations will be guided by suspected aetiology. For example:^[2]

• CXR may show an apical carcinoma of the lung.
• CT/MRI may be useful to identify a cerebrovascular accident.
• Angiography/carotid ultrasound may demonstrate dissection of the carotid artery.

Pharmacological testing

Pharmacological testing can help to confirm the diagnosis and identify if the lesion is preganglionic or postganglionic:^[7]

• Cocaine eye drops will normally cause dilatation of the pupil but there is no response in Horner's syndrome. It inhibits the reuptake of noradrenaline but this requires an intact sympathetic system. It confirms the diagnosis but does not localise the lesion. Their use was universal in the past but has been superseded by the newer agents below.
• Apraclonidine is an alternative to cocaine. It has little effect on a normal pupil but causes dilation of a pupil affected by Horner's syndrome.
• Hydroxyamphetamine 1% drops can also be instilled to both eyes but wait at least 48 hours after performing the cocaine test. The drops stimulate the release of norepinephrine from postganglionic nerves and cause dilation of the pupil (similar to that in the unaffected eye) if these nerves are intact. Hence, a first- or second-order nerve lesion will result in dilation but no dilation occurs with third-order (postganglionic) lesions.

Management

Horner's syndrome is a physical sign. Management involves diagnosis of the underlying condition and treatment as appropriate.

History

Johann Friedrich Horner was a Swiss ophthalmologist born in 1831. He was made Professor of Ophthalmology in Zurich in 1873. He described the syndrome that bears his name in 1869.^[8] In France it it called Bernard-Horner syndrome, adding the name of Claude Bernard. Horner died in Zurich in 1886. His other achievements included the observation that red-green colour blindness is transferred to males through the female line.