Horner’s Syndrome, also known as oculosympathetic palsy, is a neurological condition that results from disruption of the sympathetic nerves supplying the eye and surrounding facial structures. It is characterized by a distinctive triad of ptosis (drooping eyelid), miosis (constricted pupil), and anhidrosis (loss of sweating).
This syndrome does not represent a disease by itself but rather an important clinical sign of an underlying condition affecting the sympathetic nervous pathway. For medical students, remembering its features can be challenging, but the mnemonic “A Pretty CAMEL” makes recall easier.
Mnemonic: A Pretty CAMEL
The mnemonic A Pretty CAMEL helps recall the key features of Horner’s Syndrome:
- A – Anisocoria (unequal pupil sizes, more marked in dim light)
- P – Ptosis (drooping of the upper eyelid due to paralysis of Müller’s muscle)
- C – Convulsions (sometimes associated if due to brainstem lesions or secondary causes)
- A – Anhidrosis (reduced or absent sweating on the affected side of the face)
- M – Miosis (small pupil due to unopposed parasympathetic activity)
- E – Enophthalmos (sunken appearance of the eyeball)
- L – Loss of ciliospinal reflex (pupil fails to dilate in response to painful neck stimulation)
Pathophysiology of Horner’s Syndrome
The sympathetic pathway to the eye is a three-neuron chain:
1. First-order neuron: Originates in the hypothalamus → travels through the brainstem → descends to spinal cord (C8–T2).Disruption at any level (central, preganglionic, postganglionic) produces Horner’s Syndrome.
Causes of Horner’s Syndrome
1. Central Lesions (First-order neuron)
- Stroke (lateral medullary syndrome)
- Tumors of the brainstem
- Demyelinating diseases (multiple sclerosis)
2. Preganglionic Lesions (Second-order neuron)
- Pancoast tumor (apical lung tumor compressing sympathetic chain)
- Trauma or surgery in the neck/chest
- Thoracic aortic aneurysm
3. Postganglionic Lesions (Third-order neuron)
- Carotid artery dissection (important cause, sometimes associated with painful Horner’s)
- Cavernous sinus lesions
- Cluster headaches or migraines
Clinical Features Explained
1. Ptosis
- Mild drooping of the upper eyelid due to loss of sympathetic innervation of Müller’s muscle.
- Different from complete ptosis seen in oculomotor nerve palsy.
2. Miosis
- Pupil is constricted due to unopposed parasympathetic activity.
- More noticeable in dim light, as the affected pupil fails to dilate properly.
3. Anhidrosis
Absence of sweating on the affected side of the face.
Distribution depends on lesion site:
- Central/preganglionic → widespread facial anhidrosis
- Postganglionic → limited to forehead
4. Anisocoria
Difference in pupil size, more evident in dark environments.5. Enophthalmos
Sunken appearance of the eye, although often a relative illusion rather than true retraction.6. Loss of Ciliospinal Reflex
Normally, painful stimulation of the neck leads to pupil dilation. In Horner’s syndrome, this reflex is absent.Diagnosis
Clinical Examination
- Careful assessment of pupil size in light and dark
- Checking for ptosis and anhidrosis
- Evaluation of reflexes
Pharmacological Tests
- Cocaine test: Cocaine normally dilates pupils; failure to dilate confirms Horner’s syndrome.
- Apraclonidine test: Causes dilation of Horner’s pupil (due to denervation supersensitivity).
Imaging
- MRI/CT scan to detect central or preganglionic lesions
- CT chest for Pancoast tumor
- Carotid Doppler or MRI angiography for carotid dissection
Treatment
There is no direct treatment for Horner’s Syndrome itself. Management focuses on treating the underlying cause:
- Stroke or demyelination: Neurological management
- Pancoast tumor: Surgery, chemotherapy, or radiotherapy
- Carotid dissection: Anticoagulation or stenting
- Cluster headaches: Symptomatic treatment with oxygen and triptans
Early identification of Horner’s Syndrome is essential, as it may indicate life-threatening conditions such as carotid artery dissection or apical lung tumor.
Comparative Table: Features of Horner’s Syndrome
| Feature | Explanation | Clinical Note |
|---|---|---|
| Ptosis | Drooping eyelid due to Müller’s muscle weakness | Partial ptosis, not as severe as CN III palsy |
| Miosis | Constricted pupil | More pronounced in dim light |
| Anhidrosis | Loss of sweating | Extent depends on lesion site |
| Anisocoria | Unequal pupils | Seen more clearly in dark |
| Enophthalmos | Sunken appearance of eye | Often apparent rather than real |
| Loss of ciliospinal reflex | Absent pupillary dilation on neck pain stimulus | Diagnostic clue |
Frequently Asked Questions (FAQ)
Q1. What is the classic triad of Horner’s Syndrome?
The triad is ptosis, miosis, and anhidrosis.
Q2. Is Horner’s Syndrome always dangerous?
Not always, but it can indicate serious underlying conditions like Pancoast tumor or carotid dissection, which require urgent evaluation.
Q3. How can Horner’s Syndrome be distinguished from third cranial nerve palsy?
- Horner’s: Mild ptosis, small pupil (miosis)
- CN III palsy: Complete ptosis, large pupil (mydriasis)
Q4. Can Horner’s Syndrome occur in children?
Yes. It may be congenital (associated with birth trauma or neuroblastoma) or acquired later in life.
Q5. Which test is most commonly used today to confirm Horner’s Syndrome?
The apraclonidine test is now widely used, as it is safer and more reliable than cocaine testing.
