Neurology · Autonomic Nervous System Disorders
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Horner syndrome is defined by the classic triad of ipsilateral ptosis, miosis, and anhidrosis.
The underlying pathophysiology involves a disruption of the sympathetic chain anywhere from the hypothalamus to the orbit.
Pancoast tumors (superior sulcus tumors) are a classic cause of Horner syndrome due to involvement of the cervical sympathetic chain.
Carotid artery dissection is a critical, life-threatening etiology that must be ruled out in patients presenting with acute Horner syndrome and neck pain.
Apraclonidine is the diagnostic agent of choice because it causes pupillary dilation in the affected eye due to denervation supersensitivity.
Cocaine drops fail to dilate the affected pupil because they require intact norepinephrine release to induce mydriasis.
Anhidrosis of the face is seen with central (first-order) or preganglionic (second-order) lesions, whereas postganglionic (third-order) lesions typically spare facial sweating.
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A 54-year-old male smoker presents to the clinic complaining of a persistent cough and right-sided shoulder pain. On physical examination, the patient has right-sided ptosis, a constricted right pupil, and decreased sweating on the right side of his face. His right pupil fails to dilate with cocaine drops. A chest X-ray reveals a mass in the right lung apex.
What is the most likely underlying cause of this patient's ocular findings?
Pancoast tumor (Superior sulcus tumor)
The patient exhibits the classic triad of Horner syndrome caused by a Pancoast tumor, which disrupts the sympathetic chain at the level of the thoracic inlet.
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Etiology / Epidemiology
Caused by sympathetic chain disruption; suspect Pancoast tumor in smokers with shoulder pain.
Clinical Manifestations
Classic triad: ptosis, miosis, and anhidrosis; Horner syndrome is a clinical diagnosis.
Diagnosis
Apraclonidine eye drops confirm diagnosis; CT/MRI chest/neck identifies the underlying lesion.
Treatment
Treat the underlying cause; no direct pharmacological cure for the syndrome itself.
Prognosis
Prognosis depends on malignancy status; early detection of apical lung tumors is critical.
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Epidemiology & Etiology
Often secondary to cervical/thoracic malignancy, specifically Pancoast tumors. Other causes include carotid artery dissection, thyroidectomy complications, or cluster headaches. Always consider trauma or brainstem stroke in acute presentations.
Pertinent Anatomy
Disruption of the oculosympathetic pathway from the hypothalamus to the eye. The three-neuron arc involves the brainstem, cervical spine, and carotid sheath. Lesions proximal to the sweat glands cause ipsilateral anhidrosis.
Pathophysiology
Interruption of sympathetic outflow leads to unopposed parasympathetic tone. This results in miosis (constricted pupil) and ptosis (weakened Müller's muscle). The loss of sympathetic innervation to facial sweat glands causes the characteristic anhidrosis.
Clinical Manifestations
The triad consists of ptosis, miosis, and anhidrosis. Red flag: New-onset Horner syndrome with neck pain requires urgent imaging to rule out carotid artery dissection. Anisocoria is more pronounced in dim light due to failure of pupil dilation.
Diagnosis
Apraclonidine (alpha-2 agonist) is the gold standard for confirmation; the affected pupil will dilate while the normal pupil remains unchanged. Cocaine drops were historically used but are now obsolete. CT/MRI of the chest and neck is mandatory to localize the lesion.
Treatment
Management focuses on the underlying etiology. Do not delay imaging if dissection or malignancy is suspected. Surgical resection or radiation is indicated for Pancoast tumors. No specific medication reverses the sympathetic deficit.
Prognosis
Outcome is dictated by the primary pathology. Carotid dissection carries a high risk of stroke, while Pancoast tumors have a guarded prognosis. Long-term monitoring for metastatic disease is required.
Differential Diagnosis
Physiologic anisocoria: pupil size difference <1mm, equal in light/dark
Adie's tonic pupil: dilated pupil with sluggish light response
Third nerve palsy: ptosis with 'down and out' eye deviation
Cluster headache: episodic, severe pain with transient Horner features
Carotid artery dissection: acute Horner syndrome with ipsilateral neck/head pain