Horner syndrome (oculosympathetic palsy) is characterised by the classical triad of miosis (small and constricted pupil), partial ptosis (drooping of upper eyelid) and anhidrosis (loss of hemi facial sweating) caused due to disruption of sympathetic pathways. Von Passow syndrome is an association of Horner syndrome with heterochromia iridis (different colour in parts of same iris).
Sympathetic supply to the eye forms an arc of three neurons. First order neuron extend from posterolateral hypothalamus to ciliospinal center of Budge at cervical 8 to thoracic level 2 (C8-T2) in spinal cord.
Second order preganglionic pupillomotor fibers exit from thoracic level 1 (T1) and synapse in superior cervical ganglion at the cervical level 3 and 4 (C3-C4). Postganglionic vasomotor and sudomotor fibers innervate blood vessels and sweat glands of the face.
Third order postganglionic pupillomotor fibers joins ophthalmic division of trigeminal nerve (Vth intracranial nerve) which innervates dilator muscle of iris and Mϋller muscle in the upper lid, via long ciliary nerves.
Kanski,Jack J. Clinical Ophthalmology, A Systematic Approach .Third Edition.UK. Butterworth Heinemann, 1994.
Disruption of sympathetic pathway due to a lesion may lead to:
- Miosis or constriction of the pupil in affected eye. Dilatation of the pupil is slower after psycho sensory stimulus.
- Mild ptosis due to denervation of sympathetic nerve supply to Mϋller muscle.
- Slight elevation of the lower lid due to denervation of lower lid muscle.
- Impaired flushing and sweating ipsilaterally depending upon the site of lesion. First order neuron lesion causes anhidrosis on ipsilateral side of the body. Second order neuron lesion causes anhidrosis on ipsilateral side of face.
- Heterochromia iridis occurs in congenital Horner syndrome or in children younger than two years. Long standing Horner syndrome may also develop heterochromia.
Horner syndrome may be hereditary (autosomal dominant), congenital or acquired. Lesions may be central (involves hypothalamus or spinal cord) or peripheral (involves cervical sympathetic chain).
Different lesions may disrupt sympathetic pathways at various levels:
First order neuron lesions may occur in following conditions:
- Basal skull tumours
- Cerebrovascular accidents
- Basal meningitis
- Lesions in hypothalamus or medulla
- Arnold-Chiari malformation
- Pontine haemorrhage
- Neck trauma with high cervical cord lesion
- Pituitary tumour
- Demyelinating diseases
Second order neuron lesions may be due to conditions like:
- Pancoast tumour(carcinoma of the apex of lung)
- Birth trauma affecting lower brachial plexus
- Aneurysm or dissection of aorta
- Central venous catheterisation
- Trauma or surgical injury
- Chest tubes
- Cervical rib
Third order neuron lesions may be due to:
- Dissection of internal carotid artery
- Cluster headache
- Carotid cavernous fistula
- Herpes Zoster infection
Presenting features depends upon the underlying cause.
First order neuron lesion causes dysarthria, dysphagia, ataxia or hemisensory loss.
Second order neuron lesions may have history of prior trauma or surgery, placement of central venous line or history of chest tube application.
Third order neuron lesions may cause diplopia due to sixth cranial nerve palsy, numbness or pain in the distribution area of ophthalmic and maxillary division of trigeminal nerve ( Vth cranial nerve).
- Miosis of the pupil which dilates slowly to psycho sensory stimulus.
- Absence of horizontal eyelid crease in eye with ptosis, especially in patients with congenital Horner syndrome.
- Raised lower eyelid margin with respect to inferior limbus.
- Examination of extraocular movements may show limitation of abduction due to sixth cranial nerve palsy.
- Biomicroscopic examination may show heterochromia iridis.
- Anhidrosis (lack of sweating) and its pattern may help in localising lesion.
- Normal pupillary reactions to light and near vision.
- Apparent enophthalmos due to ptosis of upper eyelid and slight elevation of lower eyelid.
- Paradoxical retraction of contra lateral upper eyelid.
- Exclude malignancy in recently diagnosed preganglionic Horner syndrome. Patients may have associated flushing.
- Patients with postganglionic Horner syndrome may have orbital pain.
Pharmacological testing helps in identifying an ocular sympathetic lesion. Preganglionic lesions are associated with higher incidence of malignancy.
1. Cocaine test: Topical cocaine inhibits reuptake of norepinephrine from synaptic cleft and therefore acts as indirect sympathomimetic agent. Pupil dilates poorly in Horner syndrome unlike in normal eyes. Cocaine is instilled into each eye. After 40-60 minutes, an unequal size of pupil more than 0.8 mm is significant.
2. Apraclonidine test: Topical apraclonidine has no effect on normal pupil but has mydriatic (which dilates pupil) effect on abnormal pupil. There is increased sensitivity to apraclonidine in Horner syndrome. However, in acute cases, negative apraclonidine test does not exclude Horner syndrome, where cocaine test is more helpful.
3. Hydroxyamphetamine test: Topical hydroxyamphetamine releases norepinephrine from postganglionic neurons at iris dilator muscles (which dilates the pupil). Hydroxyamphetamine in cases of Horner syndrome with intact postganglionic fiber dilates affected pupil to an equal or greater extent as compared to normal pupil. However, pupil in Horner syndrome with damaged postganglionic fiber, do not dilate as well, as the normal pupil dilates.
4. Adrenaline test: Topical adrenaline (1:1000) in preganglionic lesions, does not cause dilatation of both pupils. In postganglionic lesions, due to denervation hypersensitivity, affected pupil dilates but the normal pupil does not (with this low concentration of adrenaline).
1. X-ray chest may be helpful in diagnosing apical bronchogenic carcinoma.
2. CT scan of head may be helpful in cases of stroke.
3. Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) of the brain and neck may delineate carotid artery dissection.
Many cases of Horner syndrome do not have effective treatment.
Management depends upon the underlying cause. For example, Carotid artery dissection or aneurysm requires vascular surgery. Similarly, pancoast tumour may require multi modality treatment.