Horner Syndrome

Horner syndrome is a condition resulting from an interruption of the sympathetic innervation of the eyes. The syndrome is usually idiopathic but can be directly caused by head and neck trauma, cerebrovascular disease, or a tumor of the CNS. Horner syndrome is classified as 1st-order (central), 2nd-order (preganglionic), or 3rd-order (postganglionic) based on the location of the lesion along the sympathetic pathway. Partial ptosis, miosis, and facial anhidrosis are the classical signs of Horner syndrome, making up a characteristic triad. Other associated neurologic signs may also be present, depending on the location of the lesion and can aid in determining the cause. The syndrome is diagnosed by using cocaine, apraclonidine, or hydroxyamphetamine eye drops. Management of Horner syndrome requires treatment of the underlying condition.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Definition

Horner syndrome, also known as oculosympathetic paresis, is a condition resulting from the interruption of the sympathetic supply to the eyes. The syndrome is characterized by the classic triad of: 

  • Partial ptosis (drooping or inability to raise the upper eyelid)
  • Miosis (constricted pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil)
  • Facial anhidrosis (absence of sweating)

Epidemiology

  • Can affect any age, sex, or ethnicity
  • Frequency: approximately 1 per 6000 individuals

Neuroanatomy

Horner syndrome can result from a lesion anywhere on the 3-neuron sympathetic pathway supplying the eye. The nerve supply starts from the posterolateral hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus and ends as the long ciliary nerves that supply the iris dilator and Müller muscles (superior tarsal muscle).

  • 1st-order neuron: originates in the hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus and descends to the first synapse Synapse The junction between 2 neurons is called a synapse. The synapse allows a neuron to pass an electrical or chemical signal to another neuron or target effector cell. Synapses and Neurotransmission in the cervical spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, located at levels C8–T2 (also called the ciliospinal center of Budge).
  • 2nd-order neuron: Preganglionic pupillomotor fibers exit the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord at T1, travel through the brachial plexus, over the lung apex, ascending to the superior cervical ganglion located near the angle of the mandible and the bifurcation of the common carotid artery Common carotid artery The two principal arteries supplying the structures of the head and neck. They ascend in the neck, one on each side, and at the level of the upper border of the thyroid cartilage, each divides into two branches, the external and internal carotid arteries. Carotid Arterial System
  • 3rd-order neuron: Pupillomotor fibers ascend along the internal carotid artery and enter the cavernous sinus where it is in close relation with the abducens nerve (cranial nerve (CN) VI). These fibers enter the orbit Orbit The orbit is the cavity of the skull in which the eye and its appendages are situated. The orbit is composed of 7 bones and has a pyramidal shape, with its apex pointed posteromedially. The orbital contents comprise the eye, extraocular muscles, 5 cranial nerves, blood vessels, fat, the lacrimal apparatus, among others. The Orbit and Extraocular Muscles with the ophthalmic branch (V1) of the trigeminal nerve (CN V) via the long ciliary nerves, which innervate the iris dilator and Müller muscles.
Sympathetic pathway of eye

Sympathetic pathway of the eye

Image by Lecturio. License: CC BY-NC-SA 4.0

Classification

  • 1st-order, or central, Horner syndrome: caused by lesions of the sympathetic tracts in the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem or cervicothoracic spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord
  • 2nd-order, or preganglionic, Horner syndrome: caused by lesions that involve the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, thoracic outlet, or lung apex. These lesions are usually acquired through trauma, surgery, or malignancy (e.g., Pancoast tumor).
  • 3rd-order, or postganglionic, Horner syndrome: caused by lesions of the internal carotid artery, such as arterial dissection, thrombosis, cavernous sinus aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms, or injuries acquired during carotid artery stenting

Etiology

Most cases of Horner syndrome are idiopathic. Of the identified causes, the etiology depends on the location of the lesion. The causes vary between adult and pediatric populations. 

1st-order syndrome (central)

  • Hypothalamus:
    • Stroke 
    • Tumor
  • Brain stem:
    • Stroke
    • Demyelination (e.g., multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis)
    • Tumor
  • Spinal cord:
    • Neck trauma 
    • Pituitary tumor
    • Myelitis
    • Syringomyelia
    • Demyelination (e.g., multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis)
    • Arteriovenous malformation (AVM)
    • Infarction
  • Arnold-Chiari malformation
  • Encephalitis Encephalitis Encephalitis is inflammation of the brain parenchyma caused by an infection, usually viral. Encephalitis may present with mild symptoms such as headache, fever, fatigue, and muscle and joint pain or with severe symptoms such as seizures, altered consciousness, and paralysis. Encephalitis

2nd-order syndrome (preganglionic)

  • Apical lung tumor (e.g., Pancoast tumor)
  • Subclavian artery lesions
  • Mediastinal tumors
  • Cervical rib
  • Thyroid malignancies
  • Birth trauma with injury to lower brachial plexus
  • Mandibular tooth abscess
  • Lesions of the middle ear (e.g., acute otitis media Acute Otitis Media Acute otitis media is an infection in the middle ear characterized by mucosal inflammation and retention of fluid. The most common pathogens are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. The condition can present with fever, otalgia, and diminished hearing. Acute Otitis Media)
  • Iatrogenic (e.g., central venous catheterization, chest tube placement, thoracic surgery Thoracic Surgery Basic surgical intervention in the thoracic cavity has the primary goal of alleviating any malady that mechanically affects the function of the heart and lungs, which can be secondary to underlying pathologies or, most commonly, trauma. Interventions include tube thoracostomy, thoracentesis, and emergency thoracotomy. Thoracic Surgery)

3rd-order syndrome (postganglionic)

  • Internal carotid artery dissection
  • Carotid cavernous fistula
  • Trauma
  • Herpes zoster Herpes Zoster Varicella-zoster virus (VZV) is a linear, double-stranded DNA virus in the Herpesviridae family. Shingles (also known as herpes zoster) is more common in adults and occurs due to the reactivation of VZV. Varicella-Zoster Virus/Chickenpox
  • Nasopharyngeal carcinoma, lymphoma
  • Cluster or migraine headache Migraine Headache Migraine headache is a primary headache disorder and is among the most prevalent disorders in the world. Migraine is characterized by episodic, moderate to severe headaches that may be associated with increased sensitivity to light and sound, as well as nausea and/or vomiting. Migraine Headache

Etiology of Horner syndrome in children

  • Congenital (diagnosed 4 weeks after birth):
    • Trauma to the neck and brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem during birth
    • Congenital infections
    • Neuroblastoma Neuroblastoma Neuroblastoma is a malignancy that arises from the neural crest cell derivatives along the sympathetic chain (neuroblasts) and is most commonly located in the adrenal medulla. The tumor often presents in childhood with a flank mass that crosses the midline. Neuroblastoma
    • Idiopathic
  • Acquired:
    • Neuroblastoma Neuroblastoma Neuroblastoma is a malignancy that arises from the neural crest cell derivatives along the sympathetic chain (neuroblasts) and is most commonly located in the adrenal medulla. The tumor often presents in childhood with a flank mass that crosses the midline. Neuroblastoma
    • Rhabdomyosarcoma
    • Brain stem AVMs
    • Brain stem tumors (glioma)
    • Demyelination ( brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem)
    • Carotid artery thrombosis
    • Neck trauma
    • Postsurgical (e.g., after jugular cannulation, thoracic surgery Thoracic Surgery Basic surgical intervention in the thoracic cavity has the primary goal of alleviating any malady that mechanically affects the function of the heart and lungs, which can be secondary to underlying pathologies or, most commonly, trauma. Interventions include tube thoracostomy, thoracentesis, and emergency thoracotomy. Thoracic Surgery, or neck surgery)

Pathophysiology

Horner syndrome is the result of the disruption of the sympathetic supply to the eye. The symptoms depend on the location of the lesion, and the severity depends on the severity of denervation. 

  • Denervation of the nerves that supply the Müller muscle (superior tarsal muscle) causes ptosis. Partial ptosis can occur because the levator palpebrae superioris muscle is unaffected.
  • Denervation of the nerves that supply the iris dilator muscle causes miosis of the affected side: 
    • Upon exam, anisocoria and a lag of pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil dilation can be seen. 
    • The light and accommodation pupillary reflexes remain normal. 
  • Denervation of the nerves that supply the facial sweat glands causes anhidrosis:
    • Depends on the degree of disruption of the sympathetic supply
    • Seen in 1st- or 2nd-order lesions, but not a prominent feature of 3rd-order lesions

Clinical Presentation

  • Classic triad of Horner syndrome: 
    • Ptosis
    • Miosis
    • Anhidrosis
  • Ocular signs:
    • Pupils: 
      • Miosis on the affected side
      • Anisocoria (difference in the pupillary size) that is more prominent in the dark.
      • Dilation lag (the constricted pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil takes 15–20 seconds longer to dilate when a light source is moved away from the eye.)
    • Eyelids:
      • Mild (< 2 mm) ptosis of the upper eyelid
      • Inverse ptosis of the lower eyelid (lower lid rests at a higher level than normal) 
      • Combined: decreased palpebral aperture compared to the other eye
    • Extraocular movements may be affected in lesions of the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem or the cavernous sinus.
  • Associated neurologic signs:
    • Signs of brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem lesions:
      • Ataxia
      • Diplopia
      • Lateralized weakness
      • Vertigo Vertigo Vertigo is defined as the perceived sensation of rotational motion while remaining still. A very common complaint in primary care and the ER, vertigo is more frequently experienced by women and its prevalence increases with age. Vertigo is classified into peripheral or central based on its etiology. Vertigo
    • Signs of spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord (myelopathic) lesions:
      • Ipsilateral weakness
      • Long tract signs
      • Bowel and bladder impairment
      • Spasticity
    • Brachial plexopathy Plexopathy Neuropathy is a nerve pathology presenting with sensory, motor, or autonomic impairment secondary to dysfunction of the affected nerve. The peripheral nerves are derived from several plexuses, with the brachial and lumbosacral plexuses supplying the major innervation to the extremities. Mononeuropathy (affecting a single nerve) and plexopathy (affecting the plexus) can occur from trauma, compression, and systemic diseases. Mononeuropathy and Plexopathy: pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain and weakness in the arm Arm The arm, or "upper arm" in common usage, is the region of the upper limb that extends from the shoulder to the elbow joint and connects inferiorly to the forearm through the cubital fossa. It is divided into 2 fascial compartments (anterior and posterior). Arm or hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand
    • Cranial neuropathy 
  • In infants and children, the Harlequin sign (facial flushing) is more apparent than anhidrosis. 
  • Iris heterochromia (different-colored irides) may be seen in children with congenital Horner syndrome. In these cases, the affected eye has lighter color. 
Horner syndrome

Right-sided miosis and ptosis suggestive of Horner syndrome

Image: “Myosis and eyelid ptosis were noted on the right side” by Case Reports in Endocrinology. License: CC BY 4.0

Diagnosis and Management

Clinical diagnosis

  • Horner syndrome is clinically diagnosed by the presence of ptosis and dilation lag in the affected eye. 
  • Anhidrosis is also usually observed on the same side as the affected eye but is not necessary for diagnosis. 
  • Painful acute anisocoria is highly suggestive of Horner syndrome. 

Pharmacologic tests

  • Topical cocaine can be used to confirm the diagnosis of Horner syndrome:
    • Cocaine blocks reuptake of norepinephrine from the synaptic cleft and will cause dilation of the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil in case of an intact sympathetic pathway. Cocaine has no effect on eyes with impaired sympathetic innervation.
    • 1 hour after the application of 2 drops of 10% cocaine, a normal pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil dilates more than the Horner pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil, increasing the degree of anisocoria.
    • Anisocoria ≥ 1 mm after cocaine administration is considered a positive result.
  • Topical apraclonidine is used as an alternative agent to confirm Horner syndrome: 
    • An α-adrenergic agonist that causes pupillary dilation in the Horner pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil and mild pupillary constriction in the normal eye by down-regulating norepinephrine
    • A reversal of anisocoria after the application of 2 drops of 0.5% apraclonidine is suggestive of Horner syndrome.
    • Apraclonidine should not be used in infants.
  • Topical hydroxyamphetamine is used to differentiate 1st-order and 2nd-order Horner syndrome: 
    • Hydroxyamphetamine causes a release of norepinephrine from intact adrenergic nerve endings, causing pupillary dilation.
    • 1 hour after the application of 1% hydroxyamphetamine eye drops, dilation of both pupils indicates a lesion of the 1st- or 2nd-order neuron. 
    • If the miotic pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil fails to dilate, it indicates a 3rd-order Horner syndrome.
    • Pholedrine can be used as an alternative to hydroxyamphetamine. The test is performed using 1% pholedrine.

Imaging

  • Imaging is used in conjunction with medical tests to confirm the etiology and locate the site of the lesion.
  • MRI of the brain and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord is indicated in cases with signs indicative of spinal lesions. 
  • Head CT is also advised in cases of Horner syndrome with a history of or clinical signs suggesting stroke. 
  • Chest X-ray followed by a CT scan must be performed in patients when pulmonary malignancy is suspected. 

Management

  • Depends on the underlying cause
  • Prompt recognition of the condition and diagnosis of the underlying etiology is necessary to reduce worsening of the condition. 
  • The acute painful onset of Horner syndrome should be considered a medical emergency, as it might indicate a carotid artery dissection.
  • Vascular surgical care is necessary in cases of carotid artery dissection. 
  • Neurologic care should be provided in cases of Horner syndrome related to aneurysms. 

Differential Diagnosis

  • Adie pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil: disorder of parasympathetic denervation of the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil that results in poor light constriction but better accommodation. Adie pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil is mostly idiopathic. The affected pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil initially appears abnormally dilated at rest and has a poor pupillary constriction in bright light. Patients complain of difficulty adapting to dark conditions and photophobia. No treatment is required, but topical physostigmine may provide relief. 
  • Argyll-Robertson pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil: characterized by small and irregular pupils that constrict briskly to near targets but react with little to no constriction to light. Argyll-Robertson pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil is frequently associated with iris atrophy and is a highly specific sign of neurosyphilis and is treated by managing the underlying cause. 
  • Chronic anterior uveitis Uveitis Uveitis is the inflammation of the uvea, the pigmented middle layer of the eye, which comprises the iris, ciliary body, and choroid. The condition is categorized based on the site of disease; anterior uveitis is the most common. Diseases of the Uvea: condition that affects the anterior uvea, iris, and ciliary body. The symptoms of uveitis Uveitis Uveitis is the inflammation of the uvea, the pigmented middle layer of the eye, which comprises the iris, ciliary body, and choroid. The condition is categorized based on the site of disease; anterior uveitis is the most common. Diseases of the Uvea are pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, redness, and photophobia. The symptoms respond well to antiinflammatory drugs. Chronic anterior uveitis Uveitis Uveitis is the inflammation of the uvea, the pigmented middle layer of the eye, which comprises the iris, ciliary body, and choroid. The condition is categorized based on the site of disease; anterior uveitis is the most common. Diseases of the Uvea occurs in association with other chronic inflammatory conditions. 
  • Pupillary sphincter tear: occurs because of trauma and can cause unilateral or bilateral mydriasis. Patients report glare, haloes in brightly lit conditions, and trouble reading. Patients with atonic, mydriatic pupils report worse glare at night and inability to focus on near objects. The tear requires surgical repair. 
  • Aponeurotic ptosis: most common type of acquired ptosis. Aponeurotic ptosis occurs because of outstretching of the levator muscle and is usually seen in elderly patients. Patients usually present with asymmetrical ptosis or partial vision loss. Surgical treatment is required. 
  • Ocular myasthenia: ocular representation of myasthenia gravis Myasthenia Gravis Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by weakness and fatigability of skeletal muscles caused by dysfunction/destruction of acetylcholine receptors at the neuromuscular junction. MG presents with fatigue, ptosis, diplopia, dysphagia, respiratory difficulties, and progressive weakness in the limbs, leading to difficulty in movement. Myasthenia Gravis. Ocular myasthenia results in ocular muscle fatigue and weakness. In myasthenia, antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins that block the acetylcholine receptor are produced, resulting in muscle fatigue and paralysis in some cases. Diagnosis relies on an edrophonium sodium test. Treatment involves anticholinesterase agents. 

References

  1. Kedar, S., Biousse, V., Newman, N.J. (2018). Horner syndrome. UpToDate. Retrieved June 24, 2021, from https://www.uptodate.com/contents/horner-syndrome
  2. Khan, Z., Bollu, P.C. (2021). Horner syndrome. StatPearls. Retrieved June 24, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK500000/
  3. Bardorf, C.M. (2019). Horner syndrome. Emedicine. Retrieved June 24, 2021, from https://emedicine.medscape.com/article/1220091
  4. Kanagalingam, S., Miller, N.R. (2015). Horner syndrome: clinical perspectives. Eye and Brain 2015:35–46. https://doi.org/10.2147/EB.S63633 

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