Horner's syndrome, also known as oculosympathetic paresis, is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk is damaged. The signs and symptoms occur on the same side (ipsilateral) as it is a lesion of the sympathetic trunk. It is characterized by miosis (a constricted pupil), partial ptosis (a weak, droopy eyelid), apparent anhidrosis (decreased sweating), with apparent enophthalmos (inset eyeball).

The nerves of the sympathetic trunk arise from the spinal cord in the chest, and from there ascend to the neck and face. The nerves are part of the sympathetic nervous system, a division of the autonomic (or involuntary) nervous system. Once the syndrome has been recognized, medical imaging and response to particular eye drops may be required to identify the location of the problem and the underlying cause.

Signs and symptoms

Signs that are found in people with Horner's syndrome on the affected side of the face include the following:

  • Ptosis
  • Anhidrosis: inability to sweat in a normal way.
  • Miosis
  • Enophthalmos
  • Inability to completely close or open the eyelid
  • Headaches
  • Loss of ciliospinal reflex: the pupils do not get bigger when the neck or face is hurt or pinched.
  • Bloodshot conjunctiva: The white part of the eye (the conjunctiva) looks red. How red it is can change depending on where the problem or injury is in the eye.
  • Unilateral straight hair: In congenital Horner's syndrome, the hair on the affected side of the head may be straight, whereas on the contralateral side, it is curly.
  • Heterochromia iridum

Damage to the sympathetic nerves can cause several problems. The dilator muscle, which normally makes the pupil bigger, stops working. This makes the pupil smaller (miosis). The superior tarsal muscle is in the upper eyelid and helps lift it. It stops working so the upper eyelid droops (ptosis). Sweating on the face is reduced. The eye may look sunken (enophthalmos), but this is usually just because of the drooping eyelid. True sunken eyes are rare in humans but can be seen in cats, rats, and dogs with Horner's syndrome.

The reaction of the pupils to light is normal because it does not depend on sympathetic nerve supply. or iatrogenic (caused by medical treatment or medical procedures). In rare cases, Horner's syndrome may be caused by repeated, minor head trauma, such as being hit with a soccer ball. Although most causes are relatively benign, Horner's syndrome may reflect serious disease in the neck or chest (such as a Pancoast tumor or thyrocervical venous dilatation).

Causes can be divided according to the presence and location of anhidrosis (inability to sweat):

  • Central (anhidrosis of face, arm and trunk)
  • Syringomyelia
  • Multiple sclerosis
  • Encephalitis
  • Brain tumors:
  • Cavernous sinus thrombosis
  • Middle ear infection
  • Sympathectomy
  • Nerve blocks, such as cervical plexus block, stellate ganglion or interscalene block

Pathophysiology

Horner's syndrome results from any disruption of the sympathetic innervation of the eye. The site of the lesion in the sympathetic outflow is on the ipsilateral side of the symptoms.

  1. First-order neuron (central neuron):
  2. Originates in the posterolateral side of the hypothalamus.
  3. Runs through the brainstem.
  4. Exits at the levels of C8, T1, and T2 of spinal segments, where it synapses with the second-order neuron. e.g., Central lesions affecting the Hypothalamospinal tract, like the transection of cervical spinal cord.
  5. Second-order neuron:
  • Lesions distal to the carotid bifurcation do not cause anhidrosis. This happens because the facial sweat nerves travel with the external carotid artery.

Diagnosis

thumb|Left-sided Horner's syndrome in a cat as a result of trauma, demonstrating miosis in left pupil

Diagnosis should be considered when a patient presents with anisocoria that reacts normally to light. Normal pupillary constriction should appear in both the larger and smaller pupil.

Three tests are useful in confirming the presence and severity of Horner syndrome:

  • Cocaine drop test: Cocaine eyedrops block the reuptake of post-ganglionic norepinephrine resulting in the dilation of a normal pupil from retention of norepinephrine in the synapse. However, in Horner's syndrome the lack of norepinephrine in the synaptic cleft causes mydriatic failure. However, using cocaine for diagnosing Horner's syndrome is not easy. Cocaine is a controlled drug that needs to be kept secure. At the same time, it can be difficult for patients who require drug screening due to their profession. This is because metabolites of cocaine are excreted in urine for up to 2 days after topical administration. Apraclonidine is also used in patients with glaucoma to lower intraocular pressure. In patients with unilateral Horner's syndrome its effects cause a reversal of anisocoria. In children, however, cocaine is a preferable choice because of the side effects apraclonidine has on them. Rowland Payne syndrome is a rare clinical entity characterised by the triad of ipsilateral Horner syndrome, vocal cord palsy, and hemidiaphragm paralysis. It results from simultaneous involvement of the cervical sympathetic chain, recurrent laryngeal nerve, and phrenic nerve at the lower neck or thoracic inlet. The syndrome is most often caused by malignant tumours such as breast or lung carcinoma, but may also occur after trauma or infection. It was first described by Dr Christopher Rowland Payne in 1981 following a report of three cases.

Imaging strategies

Imaging can help localize the defect in certain cases. For central Horner's syndrome MRI is recommended. The imaging is done from the brain to the upper thoracic spinal cord. In preganglionic and postganglionic Horner's syndrome, the imaging is done with computed tomography (CT) angiography from the orbits to T4-T5. When the clinical evaluation does not reveal localizing signs, the syndrome is considered isolated.

Treatment

Horner's syndrome is not considered a primary disease, but a sign of underlying conditions resulting from disruption of the sympathetic nerve pathway supplying the eye and face, which do not require direct treatment. Suitable management focuses on identifying the cause or condition that is typically secondary to lesions along the oculosympathetic pathway, such as carotid artery dissection, brainstem stroke, neoplasms (e.g., Pancoast tumor), trauma, or demyelinating diseases. There can be varied treatments based on the etiology: Vascular (carotid dissection) may need anticoagulation or antiplatelet therapy while neoplastic may need surgery, radiation, or chemotherapy. As a rule, the ptosis and miosis induced by Horner syndrome will not require treatment as a primary concern, although apraclonidine eye drops or eyelid surgery can provide short-term cosmetic benefit in some cases.

Urgent assessment is necessary when symptoms come on acutely with neck pain or neurologic deficits, as these may reflect life-threatening processes such as carotid dissection or intracranial lesions. The symptoms will usually resolve spontaneously or after the underlying condition is treated successfully.

History

The syndrome is named after Johann Friedrich Horner, the Swiss ophthalmologist who first described the syndrome in 1869. Several others had previously described cases, but "Horner's syndrome" is most prevalent. In France and Italy, Claude Bernard is also eponymized with the condition (Claude Bernard–Horner syndrome, abbreviated CBH). In France, Francois Pourfour du Petit is also credited with describing this syndrome.

Children

The most common causes in young children are birth trauma and a type of cancer called neuroblastoma. Isolated Horner syndrome can be the first symptom of neuroblastoma. The cause of about a third of cases in children is unknown.