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Horner's Syndrome
Overview
- Horner’s syndrome develops from injury to anywhere along the C8-T2 sympathetic pathway: as proximal as the hypothalamus to as distal as the post-ganglionic sympathetic fibers. Localizations include the hypothalamus, medulla, ciliospinal center of Budge (C8 - T2), superior cervical ganglion, carotid artery.
The sympathetic pathology, called Horner's syndrome, manifests with, amongst other pathologic signs:
- Ptosis, which is eyelid droop; we can detect it if we compare the palpebral fissure size of the normal eye to the abnormal eye; here it will be more narrow because of the eyelid droop, from loss of superior tarsal muscle tone.
- Miosis, pupil constriction, from a loss of innervation to the dilator muscles.
- Anhidrosis, loss of sweating, from loss of sympathetic innervation to sweat glands to the face.
Common causes of Horner's syndrome
Key Anatomy
- Sympathetic circuitry begins within the hypothalamus.
- Descends via the posterolateral hypothalamospinal tract.
- Innervates the ciliospinal center of Budge at C8 – T2.
- Innervates the superior cervical ganglion, which sends fibers that ascend the carotid artery to innervate the head and neck.
Key causes of Horner's syndrome are, from proximal to distal:
- Hypothalamic dysautonomia
- For example from hypothalamic hemorrhage. The thalamus is a common site of intracranial hemorrhage (ICH) and hemorrhage can extend into and injure the hypothalamus.).
- Brainstem strokes (typically, medullary).
- Pancoast tumor (a form of apical lung tumor) and other paravertebral masses.
- Carotid dissection expands the vessel wall and injures the surrounding ascending sympathetic fibers.
- Note that the external carotid artery fibers carry the facial sweat response. So, if the external carotid fibers are spared, facial sweating will remain intact.
The Cocaine Test
Cocaine will not dilate the pupil (mechanism of its action is blockade of reuptake of dopamine and noradrenaline) and adrenaline dilates it more than usual (Cannon’s law of denervation supersensitivity).
The Cocaine Test
In the cocaine test in Horner’s syndrome, cocaine will not dilate the pupil.
This is because cocaine’s mechanism of its action is blockade of reuptake of dopamine and noradrenaline but these neurotransmitters can’t be released to begin with because the iris is denervated.
In contrast, direct adrenaline drops produces exaggerated dilation – this is Cannon’s law of denervation supersensitivity.