Not a feature of Horner syndrome:
**Core Concept**
Horner syndrome is a neurological disorder characterized by the disruption of the sympathetic nerves supplying the eye, resulting in a classic triad of ptosis, miosis, and anhidrosis. This condition is often caused by a lesion or damage to the sympathetic pathways, which can be due to various reasons such as stroke, trauma, or tumors.
**Why the Correct Answer is Right**
The correct answer is not a feature of Horner syndrome because Horner syndrome is specifically defined by the absence of these symptoms. The correct features of Horner syndrome include ptosis (drooping of the eyelid), miosis (constricted pupil), and anhidrosis (absence of sweating on the face). The presence of these symptoms is a key diagnostic criterion for Horner syndrome.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Horner syndrome is characterized by ptosis, not enophthalmos (sinking of the eye into the orbit). Enophthalmos is actually a feature of other conditions, such as orbital fractures.
* **Option B:** This option is incorrect because Horner syndrome is characterized by miosis, not mydriasis (dilated pupil). Mydriasis is actually a feature of other conditions, such as anticholinergic toxicity.
* **Option C:** This option is incorrect because Horner syndrome is characterized by anhidrosis, not hyperhidrosis (excessive sweating). Hyperhidrosis is actually a feature of other conditions, such as hyperhidrosis syndrome.
**Clinical Pearl / High-Yield Fact**
One key feature to remember about Horner syndrome is that it is a "sympathetic oculosympathetic" disorder, meaning that it affects the sympathetic nerves supplying the eye. This is in contrast to other conditions that affect the parasympathetic nerves, such as oculomotor nerve palsy.
**Correct Answer:** D