HORNERS SYNDROME - CAUSES AND DIAGNOSIS

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Horners syndrome is known by many names including Bernard-Horner syndrome and oculo-sympathetic palsy. The syndrome was named after the Swiss ophthalmologist who first described it in 1869; the condition had also been eponymized in France by Claude Bernard – hence the name, Bernard-Horner syndrome.

Horners syndrome is primarily due to damage of sympathetic nerves supplying the eye and is characterized by enophthalmos (sinking of the eyeball into the orbit), partial ptosis (drooping upper eyelid), swelling of the lower eyelid, miosis (constricted pupil), loss of sweating on the affected side of the face and heterochromia (difference in eye color).

To understand why Horners syndrome occurs, it is important to take a moment to describe the innervation of the eye. The entire nervous system can be grouped as voluntary (hence, it is under your control e.g. muscle movement) and the involuntary (also called the autonomic nervous system because it is automatic). The autonomic nervous system is further divided into a sympathetic system and a parasympathetic system.

The organs, glands, muscles, blood vessels receive both sympathetic and parasympathetic nervous supplies and in most cases, the two divisions of the autonomic nervous system have opposing effects in the organs they supply. In the eye, the sympathetic system dilates the pupillary muscles (when the pupils dilate, more light enters into the eyes – so you see clearly at night) and relaxes the ciliary muscle. The parasympathetic system has opposing effects; it constricts both the pupillary and ciliary muscles of the eye. Contraction and relaxation of the ciliary muscle alters the curvature of the lens allowing you to see near and far objects, respectively.

The sympathetic nerves that supply the eye originate in the brain but their journey to the eye is complex. There are four neuronal pathways from the brain to the eye; the first begins in the cerebrum of the brain and runs down the spinal cord into the chest. The second neuronal pathway begins in the chest and over the lungs, along the carotid vessels up into the neck. The third neuronal pathway starts at where the second neuronal pathway ended, moving through the middle ear and finally into the eye. On entering the eye, the nerves split in two – one branch innervates the pupil and the other branch supplies the muscles of the eyelid.

This complex pathway can be disrupted at any point in its journey from the brain to the eye – Horner syndrome is the result of a disruption in the sympathetic pathway; the clinical features described above result from unopposed parasympathetic action in the affected eye.

Causes of Horners Syndrome

By itself the syndrome is not a disease but a sign of an underlying and often serious condition. There are three groups of Horner syndrome, receiving its name from the sympathetic pathway where the disruption occurred.

    First Neuron Horner Syndrome – is caused by a disruption along the first neuronal pathway which may be due to:

    • Arnold-Chiari malformation
    • Wallenberg syndrome
    • Cerebrovascular accident (commonly called a stroke)
    • Basal skull tumors
    • Pituitary tumor
    • Syringomyelia
    • Basal meningitis (e.g. syphilis)
    • Demyelinating disease (e.g. multiple sclerosis)
    • Intrapontine hemorrhage
    • Neck trauma (e.g. traumatic dislocation of the cervical vertebrae)

    Second Neuron Horners Syndrome – is a disruption along the second neuronal pathway which may be due to:

    • Pancoast tumor (a tumor in the apex of the lung)
    • Birth trauma with injury to lower brachial plexus
    • Cervical rib
    • Aortic aneurysm
    • Lymphadenopathy (Hodgkin disease, leukemia, tuberculosis, mediastinal tumors)
    • Mandibular tooth abscess
    • Lesions of the middle ear (e.g. acute otitis media)
    • Phrenic nerve syndrome
    • Severe osteoarthritis of the neck with bone spurs
    • Neuroblastoma
    • Neck trauma secondary to injury or surgery (e.g. radical neck dissection, thyroidectomy, carotid angiography, coronary artery bypass graft)

    Third Neuron Horners Syndrome Group I – may be caused by

    • Raeder syndrome (Paratrigeminal syndrome)
    • Cluster /migraine headaches
    • Herpes zoster
    • Carotid cavernous fistula

    Third Neuron Horners Syndrome Group II – involves the facial sweating mechanism

Drugs may only cause symptoms similar to Horner syndrome, these drugs include: Acetophenazine, Alseroxylon, Bupivacaine, Butaperazine, Carphenazine, Chloroprocaine, Chlorpromazine, Deserpidine, Diacetylmorphine, Diethazine, Ethopropazine, Etidocaine, Fluphenazine, Guanethidine, Influenza virus vaccine, Levodopa, Lidocaine, Mepivacaine, Mesoridazine, Methdilazine, Methotrimeprazine, Oral contraceptives, Perazine, Prilocaine, Procaine, Prochlorperazine, Promazine, Promethazine, Propoxycaine, Reserpine, Thioproperazine, Thioridazine and Trifluoperazine.

Quite rarely, Horners syndrome could be congenital (inherited). When this occurs, it sometimes leads to differences in eye color between the two eyes (heterochromia). This occurs because absence of sympathetic stimulation in childhood interferes with the production of the melanin pigment by melanin producing cells in the iris.

The syndrome isn’t only caused by direct injury along the sympathetic nerve pathway. It may also be the result of viral infections, immune mediated and idiopathic (unknown) pathologies.

Diagnosing Horners Syndrome

    Diagnosing this condition is by taking a detailed history and performing a physical examination on the patient; it may also be important to carry out investigations. Investigations to diagnose this disorder include:

    • Cocaine drop test – This test is used to detect an ocular sympathetic lesion. Two drops of 4% or 10% cocaine solution are instilled into each eye. Cocaine is a sympathomimetic meaning that when given, it stimulates the sympathetic nervous system, producing pupillary and ciliary muscle dilation in the eye. The normal response in the presence of an intact sympathetic supply is pupillary dilation however, if the sympathetic supply to the pupils have been disrupted at some point, there is no pupillary response.
    • Paredrine test – This is another test used to detect a 3rd neuron Horner syndrome lesion using 1% hydroxyamphetamine.
    • Apraclonidine test

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