FFS: Horner Syndrome

Horner syndrome is a neurologic syndrome that classically presents with:

1. Miosis – producing an obvious anisocoria (unequal pupil sizes)
2. Ptosis
3. Anhidrosis
4. Enophthalmos – actually a pseudoenophthalmos, where the eye appears sunken due to narrowing of the palpebral aperture from ptosis

Horner’s syndrome results from a lesion of the ipsilateral sympathetic innervation to the eye, anywhere along the neural pathway:

• Brainstem – hypothalamus, sympathetic nucleus
• Cervical and upper thoracic spinal cord
• Sympathetic chain and stellate ganglion
• Carotid sympathetic plexus

Causes range from benign to serious.

History

The syndrome is eponymously attributed to Swiss ophthalmologist Johann Friedrich Horner (1831-1886), who published a comprehensive case in 1869.

However, earlier descriptions exist, notably by François Pourfour du Petit (1664–1741), Edward Selleck Hare (1812-1838), and Silas Weir Mitchell (1829-1914), prompting historical debate over attribution. In France, the condition is known as Bernard-Horner syndrome, acknowledging Claude Bernard’s experimental work.

Anatomy

Horner’s syndrome involves a three-neuron sympathetic pathway originating in the hypothalamus:

1. First-order neurons – descend to the cervical spinal cord (C8–T2)
2. Second-order neurons – travel through the sympathetic trunk, brachial plexus, over the lung apex, then ascend to the superior cervical ganglion near the mandible
3. Third-order neurons – ascend with the internal carotid artery, pass through the cavernous sinus (near CN VI), and join the ophthalmic division of CN V to innervate the iris dilator and Müller’s muscle

Pathophysiology

Causes

Congenital

• Can occur with birth trauma
• Associated with heterochromia (affected iris lighter)

Acquired – best classified by anatomical region:

1. Brainstem / upper spinal cord
   • Vascular (e.g. lateral medullary syndrome)
   • Tumour
   • Syringobulbia, syringomyelia
   • Demyelination (e.g. MS)
2. Neck
   • Tumour (e.g. thyroid, lymph nodes)
   • Trauma or surgery
   • Vascular: carotid dissection, aneurysm, arteritis
3. Chest
   • Apical lung tumours (Pancoast) – look for T1 signs
4. Intracranial (non-brainstem)
   • Carotid aneurysms
   • Cavernous sinus disease (e.g. cluster headache)

Note: In many cases, no cause is found.

Clinical features

“Everything gets smaller” in Horner’s syndrome

1. Partial ptosis – mild (<2 mm), affects Müller’s muscle. May involve lower lid (upside-down ptosis).
2. Miosis – small pupil with normal reflexes; anisocoria more prominent in dark.
   • In congenital cases, heterochromia may be present.
3. Anhidrosis – facial anhidrosis present in central/pre-ganglionic lesions, often absent in postganglionic lesions
4. Enophthalmos – apparent, not true, due to ptosis

Associated neurological features

These help localise the lesion:

• Brainstem signs (e.g. diplopia, vertigo) → brainstem
• Myelopathy (weakness, long tract signs) → cervicothoracic cord
• Brachial plexus signs (arm pain/weakness) → lung apex
• Isolated CN VI palsy → cavernous sinus
• Horner’s with neck pain/mass → carotid dissection

Investigations

Tailored to suspected cause:

• CXR – apical lung mass
• Carotid Doppler ultrasound – initial screen
• CT / CT angiogram – head, neck, chest, carotids
• MRI / MRA – best for brainstem, spinal cord, carotids (avoids contrast)

Management

• Treatment is directed at the underlying cause.

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References

Publications

• Horner JF. Über eine Form von Ptosis. Klinische Monatsblätter für Augenheilkunde 1869;7:193-198
• Kisch B. Horner’s syndrome, an American discovery. Bull Hist Med. 1951 May-Jun;25(3):284-8.
• Onuigbo WI. John Reid (1809-49) and Horner’s syndrome. Scott Med J. 1958 May;3(5):218-20.

FOAMed

• Cadogan M. Horner Syndrome. LITFL
• Cadogan M. Johann Friedrich Horner. LITFL
• Nickson C. Horner Syndrome. LITFL
• Nickson C. Horner syndrome DDx. LITFL